Immunogenic compositions containing inactivated influenza b virus and cpg oligonucleotide adjuvant and uses thereof

Abstract

Provided herein are immunogenic compositions comprising a mosaic influenza B virus hemagglutinin (HA) and a CpG oligonucleotide adjuvant. Also provided herein are immunogenic compositions comprising an inactivated influenza B virus described herein or inactivated split influenza B virus described herein and a CpG oligonucleotide adjuvant described herein, wherein the inactivated influenza B virus or inactivated split influenza B virus comprises a mosaic HA described herein. The immunogenic compositions may be used in a sequential immunization regimen. Also provided herein are methods of immunizing a subject against influenza virus disease (e.g., influenza virus disease caused by influenza B virus) using an immunogenic composition described herein. Further, provided herein are methods of preventing influenza virus disease (e.g., influenza virus disease caused by influenza B virus) in a subject using an immunogenic composition described herein.

Description

IMMUNOGENIC COMPOSITIONS CONTAINING INACTIVATED INFLUENZA B VIRUS AND CpG OLIGONUCLEOTIDE ADJUVANT AND USES THEREOFCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 559,757, filed February 29, 2024, the disclosure of which is incorporated by reference herein in its entirety.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0002] This invention was made with government support under AI097092, and AI145870 awarded by the National Institute of Health, the Collaborative Influenza Vaccine Innovation Centers (CIVIC) contract 75N93019C00051, and the Centers of Excellence for Influenza Research and Response contract 75N93021C00014. The government has certain rights in this invention.SEQUENCE LISTING

[0003] This application contains an electronic Sequence Listing which has been submitted in XML file format with this application, the entire content of which is incorporated by reference herein in its entirety. The Sequence Listing XML file submitted with this application is entitled “06923-424-228_SEQ_LISTING.xml”, was created on February 24, 2025, and is 128,939 bytes in size.1. INTRODUCTION

[0004] Provided herein are immunogenic compositions comprising a mosaic influenza B virus hemagglutinin (HA) and a CpG oligonucleotide adjuvant. Also provided herein are immunogenic compositions comprising an inactivated influenza B virus described herein or inactivated split influenza B virus described herein and a CpG oligonucleotide adjuvant described herein, wherein the inactivated influenza B virus or inactivated split influenza B virus comprises a mosaic HA described herein. The immunogenic compositions may be used in a sequential immunization regimen. Also provided herein are methods of immunizing a subject against influenza virus disease e.g., influenza virus disease caused by influenza B virus) using an immunogenic composition described herein. Further, provided herein are methods of preventing influenza virus disease (e.g., influenza virus disease caused by influenza B virus) in a subject using an immunogenic composition described herein.2. BACKGROUND

[0005] Seasonal influenza viruses represent a major public health burden every year. The vaccine effectiveness (VE) of commercially available influenza vaccines is in the range of 10-60% (Okoli et al., 2021, Vaccine 39: 1225-1240). The rapid antigenic evolution of influenza viruses (Neher et al., 2016, Proc Natl Acad Sci USA 113 :E1701 - 1709), the acquisition of TV-linked glycans in the immunodominant hemagglutinin (HA) head domain (Suzuki, 2011, Genes Genet Syst 86:287-294), and egg-adaptive mutations (Rajaram et al., 2020, Vaccine 38:6047-6056) may be the main reasons for the lower VE for these vaccines. Despite their low pandemic risk, influenza B viruses account for 20 to 30% of all influenza cases (FIG. 1A) (Koutsakos and Kent, 2021, Microbiology Australia 42: 110-115; Koutsakos et al., 2016, Future Microbiol 11 : 119-35). In some years, they have been the most prominent circulating strains, causing high mortality in infants and children (Noelle-AMv et al., 2007, Vaccine 25:5086-5096; Dijkstra et al., 2009, Epidemiol Infect 137:473-479; Terho et al., 2014, Clin Infect Dis 59: 1519-1524; Herman et al., 2012, Influenza Other Resp 7:313-320). The ever-mutating influenza B viruses pose a potential pandemic threat.

[0006] Current influenza virus vaccines are composed of the matched group 1, group 2, and influenza B virus circulating strains. The immune response elicited by these vaccines mainly targets the immunodominant head domain of the most abundant influenza virus glycoprotein, the HA. The head domain of the HA is subject to strong antigenic drift and can accommodate mutations that facilitate escape from pre-existing immunity, hence annual revaccinations are required. Moreover, seasonal influenza virus vaccines would offer little to no protection against pandemic influenza viruses. The development of broadly protective vaccines is therefore of high importance (Kanekiyo and Graham, 2020, Cold Spring Harbor Perspectives in Medicine a038448; Krammer et al., 2018, Cold Spring Harb Perspect Biol 10).3. SUMMARY

[0007] In one aspect, provided herein are immunogenic compositions comprising a mosaic hemagglutinin (HA) described herein and a CpG oligonucleotide adjuvant described herein. In some embodiments, the immunogenic composition further comprises an aluminum salt (e.g., amorphous aluminum hydroxyphosphate sulfate, aluminum hydroxide, aluminum phosphate, or potassium aluminum sulfate). In some embodiments, the mosaic HA comprises an HA ectodomain of an influenza B virus HA in which immunodominant epitopes in one or more (e.g., 1, 2, 3, or 4) major antigenic sites (e.g., the 120 loop, the 150loop, the 160 loop, and / or 190 helix) in the globular head domain of the HA ectodomain are silenced. In some embodiments, the mosaic HA comprises an influenza B virus HA ectodomain in which immunodominant epitopes in one or more (e.g., 1, 2, 3, or 4) major antigenic sites (e.g., the 120 loop, the 150 loop, the 160 loop, and / or 190 helix) in the globular head domain of the HA ectodomain are replaced with corresponding sequences from influenza A virus HA (e.g., exotic influenza A virus HAs, such as, e.g., H5, H8, Hl 1, or Hl 3). In some embodiments, the mosaic HA further comprises transmembrane and cytoplasmic domains of the influenza B virus HA. In some embodiments, the influenza A virus HA is influenza virus A / Vietnam / 1203 / 2004 HA, influenza virus A / mallard / Sweden / 24 / 2002 HA, influenza virus A / shoveler / Netherlands / 18 / 99 HA, or influenza virus A / black-headed gull / / Sweden / l / 1999 HA. In some embodiments, the CpG oligonucleotide adjuvant comprises an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84). In some embodiments, the oligonucleotide comprises the nucleotide sequence of 5’- TGACTGTGAACGTTCGAGATGA-3’ (SEQ ID NO: 85).

[0008] In some embodiments, provided herein is a immunogenic composition, comprising: (a) a mosaic HA comprising an HA ectodomain of an influenza B virus HA, wherein the HA ectodomain comprises (A) an HA stalk domain of the influenza B virus HA, and (B) an HA globular head domain of the influenza B virus HA with amino acid changes (e.g., substitutions) in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain, and 0, 1, 2, or 3 compensatory amino acid substitutions outside of the 120 loop, the 150 loop, the 160 loop, and the 190 helix, wherein: (i) the amino acid changes (e.g., substitutions) in the 120 loop comprise 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid changes (e.g., substitutions), and wherein the amino acid changes (e.g., substitutions) change (e.g., substitute) 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the 120 loop of the globular head domain of the influenza B virus HA to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA; (ii) the amino acid changes (e.g., substitutions) in the 150 loop comprise 2, 3, 4, 5, 6, or 7 amino acid changes (e.g., substitutions), and wherein the amino acid changes (e.g., substitutions) change (e.g., substitute) 2, 3, 4, 5, 6, or 7 amino acid residues in the 150 loop of the globular head domain of the influenza B virus HA to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA; (iii) the amino acid changes (e.g., substitutions) in the 160 loop comprise 2, 3, 4, 5, or 6 amino acid changes (e.g., substitutions), and wherein the amino acid changes (e.g., substitutions) change (e.g.,substitute) 2, 3, 4, 5, or 6 amino acid residues in the 160 loop of the globular head domain of the influenza B virus HA to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA; and (iv) the amino acid changes (e.g., substitutions) in the 190 helix comprise 2, 3, 4, 5, or 6 amino acid changes (e.g., substitutions), and wherein the amino acid changes (e.g., substitutions) change (e.g., substitute) 2, 3, 4, 5, or 6 amino acid residues in the 190 helix of the globular head domain of the influenza B virus HA to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA; and b) a CpG oligonucleotide adjuvant comprising an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84). In some embodiments, the oligonucleotide comprises the nucleotide sequence of 5’- TGACTGTGAACGTTCGAGATGA-3’ (SEQ ID NO: 85). In some embodiments, the influenza A virus is an influenza A virus H5, H8, Hl 1, or Hl 3 subtype. In some embodiments, the mosaic HA further comprises transmembrane and cytoplasmic domains of the influenza B virus HA. In some embodiments, the influenza B virus HA is B / Yamagata / 16 / 1988 HA. In some embodiments, the influenza B virus HA comprises the amino acid sequence of SEQ ID NO: 91. In some embodiments, the influenza B virus HA is B / Brisbane / 60 / 2008 HA. In some embodiments, the influenza B virus HA comprises the amino acid sequence of SEQ ID NO: 92. In some embodiments, the influenza B virus HA is B / Phuket / 3073 / 2013 HA. In some embodiments, the influenza B virus HA comprises the amino acid sequence of SEQ ID NO: 93. In some embodiments, the influenza A virus HA is influenza virus A / Vietnam / 1203 / 2004 HA, influenza virus A / mallard / Sweden / 24 / 2002 HA, influenza virus A / shoveler / Netherlands / 18 / 99 HA, or influenza virus A / black-headed gull / / Sweden / l / 1999 HA. In some embodiments, the influenza B virus HA is B / Yamagata / 16 / 1988 HA and the amino acid changes in the 120 loop, 150 loop, 160 loop, and 190 helix comprise those provided in Table 2 for mH5 / BYam, mH8 / BYam, mHl 1 / BYam, or mH13 / BYam. In some embodiments, the influenza B virus HA is B / Brisbane / 60 / 2008 HA and the amino acid changes in the 120 loop, 150 loop, 160 loop, and 190 helix comprise those provided in Table 2 for mH13 / BBris. In some embodiments, the influenza B virus HA is B / Phuket / 3073 / 2013 HA and the amino acid changes in the 120 loop, 150 loop, 160 loop, and 190 helix comprise those provided in Table 2 for mH5 / Bphu. In some embodiments, the immunogenic composition further comprises an aluminum salt (e.g., amorphous aluminum hydroxyphosphate sulfate, aluminum hydroxide, aluminum phosphate, or potassium aluminum sulfate).

[0009] In some embodiments, provided herein is an immunogenic composition, comprising: (a) an inactivated influenza virus (e.g., influenza B virus) or an inactivated split influenza virus (e.g., influenza B virus) comprising a mosaic HA, wherein the mosaic HA comprises an HA ectodomain of an influenza B virus HA, wherein the HA ectodomain comprises (A) an HA stalk domain of the influenza B virus HA, and (B) an HA globular head domain of the influenza B virus HA with amino acid changes (e.g., substitutions) in the 120 loop, 150 loop, 160 loop, and 190 helix, and 0, 1, 2, or 3 compensatory amino acid substitutions outside of the 120 loop, the 150 loop, the 160 loop, and the 190 helix, wherein: (i) the amino acid changes (e.g., substitutions) in the 120 loop comprise 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid changes (e.g., substitutions), and wherein the amino acid changes (e.g., substitutions) change (e.g., substitute) 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the 120 loop of the globular head domain of the influenza B virus HA to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA; (ii) the amino acid changes (e.g., substitutions) in the 150 loop comprise 2, 3, 4, 5, 6, or 7 amino acid changes (e.g., substitutions), and wherein the amino acid changes (e.g., substitutions) change (e.g., substitute) 2, 3, 4, 5, 6, or 7 amino acid residues in the 150 loop of the globular head domain of the influenza B virus HA to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA; (iii) the amino acid changes (e.g., substitutions) in the 160 loop comprise 2, 3, 4, 5, or 6 amino acid changes (e.g., substitutions), and wherein the amino acid changes (e.g., substitutions) change (e.g., substitute) 2, 3, 4, 5, or 6 amino acid residues in the 160 loop of the globular head domain of the influenza B virus HA to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA; and (iv) the amino acid changes (e.g., substitutions) in the 190 helix comprise 2, 3, 4, 5, or 6 amino acid changes (e.g., substitutions), and wherein the amino acid changes (e.g., substitutions) change (e.g., substitute) 2, 3, 4, 5, or 6 amino acid residues in the 190 helix of the globular head domain of the influenza B virus HA to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA; and (b) a CpG oligonucleotide adjuvant comprising an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84). In some embodiments, the oligonucleotide comprises the nucleotide sequence of 5’- TGACTGTGAACGTTCGAGATGA-3’ (SEQ ID NO: 85). In some embodiments, the influenza A virus is an influenza A virus H5, H8, Hl 1, or Hl 3 subtype. In some embodiments, the mosaic HA further comprises transmembrane and cytoplasmic domains ofthe influenza B virus HA. In some embodiments, the influenza B virus HA is B / Yamagata / 16 / 1988 HA. In some embodiments, the influenza B virus HA comprises the amino acid sequence of SEQ ID NO: 91. In some embodiments, the influenza B virus HA is B / Brisbane / 60 / 2008 HA. In some embodiments, the influenza B virus HA comprises the amino acid sequence of SEQ ID NO: 92. In some embodiments, the influenza B virus HA is B / Phuket / 3073 / 2013 HA. In some embodiments, the influenza B virus HA comprises the amino acid sequence of SEQ ID NO: 93. In some embodiments, the influenza A virus HA is influenza virus A / Vietnam / 1203 / 2004 HA, influenza virus A / mallard / Sweden / 24 / 2002 HA, influenza virus A / shoveler / Netherlands / 18 / 99 HA, or influenza virus A / black-headed gull / / Sweden / l / 1999 HA. In some embodiments, the influenza B virus HA is B / Yamagata / 16 / 1988 HA and the amino acid changes in the 120 loop, 150 loop, 160 loop, and 190 helix comprise those provided in Table 2 for mH5 / BYam, mH8 / BYam, mHl 1 / Byam, or mH13 / BYam. In some embodiments, the influenza B virus HA is B / Brisbane / 60 / 2008 HA and the amino acid changes in the 120 loop, 150 loop, 160 loop, and 190 helix comprise those provided in Table 2 for mH13 / BBris. In some embodiments, the influenza B virus HA is B / Phuket / 3073 / 2013 HA and the amino acid changes in the 120 loop, 150 loop, 160 loop, and 190 helix comprise those provided in Table 2 for mH5 / Bphu. In some embodiments, the immunogenic composition further comprises an aluminum salt (e.g., amorphous aluminum hydroxyphosphate sulfate, aluminum hydroxide, aluminum phosphate, or potassium aluminum sulfate).

[0010] In some embodiments, provided herein is an immunogenic composition, comprising: (a) a mosaic HA comprising the amino acid sequence of SEQ ID NO: 38, 40, 42, 44, 46, or 48; and (b) a CpG oligonucleotide adjuvant comprising an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84). In some embodiments, provided herein is an immunogenic composition, comprising: (a) an inactivated influenza virus (e.g., an inactivated influenza B virus) or an inactivated split influenza virus (e.g., an inactivated split influenza B virus) comprising a mosaic HA, wherein the mosaic HA comprises the amino acid sequence of SEQ ID NO: 38, 40, 42, 44, 46, or 48; and (b) a CpG oligonucleotide adjuvant comprising an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84). In some embodiments, the oligonucleotide comprises the nucleotide sequence of 5’-TGACTGTGAACGTTCGAGATGA-3’ (SEQ ID NO: 85). In some embodiments, the immunogenic composition further comprises analuminum salt (e.g., amorphous aluminum hydroxyphosphate sulfate, aluminum hydroxide, aluminum phosphate, or potassium aluminum sulfate).

[0011] In some embodiments, an immunogenic composition described herein is used in accordance with a method described herein. In some embodiments, an immunogenic composition described herein is for use in a method for inducing an immune response (e.g., a cross-reactive immune response to at least two influenza B viruses) in a subject (e.g., a human). In some embodiments, an immunogenic composition described herein is for use in a method for immunizing a subject (e.g., a human) against influenza virus disease (e.g., influenza virus disease caused by an influenza B virus). In some embodiments, an immunogenic composition described herein is for use in a method for preventing influenza virus disease (e.g., influenza virus disease caused by an influenza B virus) in a subject (e.g., a human).

[0012] In some embodiments, provided herein is a method for inducing an immune response (e.g., a cross-reactive immune response to at least two influenza B viruses) in a subject (e.g., a human) comprising administering to the subject an immunogenic composition described herein. In some embodiments, provided herein is a method for immunizing a subject (e.g., a human) against influenza virus disease (e.g., influenza virus disease caused by an influenza B virus) comprising administering to the subject an immunogenic composition described herein. In some embodiments, provided herein is a method for preventing influenza virus disease (e.g., influenza virus disease caused by an influenza B virus) in a subject (e.g., a human) comprising administering to the subject an immunogenic composition described herein. In some embodiments, the immunogenic composition is administered to the subject intramuscularly or intranasally. In some embodiments, the methods include the administration of more than one immunogenic composition described herein to a subject (e.g., a human). For example, a first immunogenic composition described herein may be administered to a subject (e.g., a human) to prime the immune response and one, two, or more boosters of immunogenic compositions described herein may be administered to the subject. In some embodiments, the mosaic HA in each immunogenic composition is different.

[0013] In some embodiments, provided herein is the use of an immunogenic composition described herein in the manufacture of a medicament for inducing an immune response (e.g., an immune response that is capable of cross-reacting with a plurality of influenza B virus strains and lineages) in a subject (e.g., human subject). In some embodiments, provided herein is the use of an immunogenic composition described herein in the manufacture of amedicament for immunizing a subject (e.g., a human) against influenza virus disease (e.g., influenza virus disease caused by an influenza B virus). In some embodiments, provided herein is the use of an immunogenic composition described herein in the manufacture of a medicament for preventing influenza virus disease (e.g., influenza virus disease caused by an influenza B virus) a subject (e.g., a human).

[0014] In some embodiments, provided herein are methods of inducing an immune response (e.g., an immune response that is capable of cross-reacting with a plurality of influenza B virus strains and lineages) in a subject (e.g., human subject), comprising sequentially administering to the subject two or more immunogenic compositions described herein, wherein one or more (e.g., two or more) of the immunogenic compositions comprises a mosaic HA, and wherein each mosaic HA is different from each other. In some embodiments, provided herein are methods of inducing an immune response (e.g., an immune response that is capable of cross-reacting with a plurality of influenza B virus strains and lineages) in a subject (e.g., human subject), comprising sequentially administering to the subject two or more immunogenic compositions described herein, wherein one or more (e.g., two or more) of the immunogenic compositions comprises an inactivated or an inactivated split influenza B virus and a CpG oligonucleotide adjuvant described herein, wherein each inactivated or inactivated split influenza B virus comprises a mosaic HA, and wherein each mosaic HA is different from each other.

[0015] In some embodiments, provided herein are methods of immunizing a subject (e.g., a human) against influenza virus disease (e.g., influenza virus disease caused by an influenza B virus), comprising sequentially administering to the subject two or more immunogenic compositions described herein, wherein one or more (e.g., two or more) of the immunogenic compositions comprises a mosaic HA, and wherein each mosaic HA is different from each other. In some embodiments, provided herein are methods of immunizing a subject (e.g., a human) against influenza virus disease (e.g., influenza virus disease caused by an influenza B virus), comprising sequentially administering to the subject two or more immunogenic compositions described herein, wherein one or more (e.g., two or more) of the immunogenic compositions comprises an inactivated or an inactivated split influenza B virus and a CpG oligonucleotide adjuvant described herein, wherein each inactivated or inactivated split influenza B virus comprises a mosaic HA, and wherein each mosaic HA is different from each other.

[0016] In some embodiments, provided herein are methods of preventing influenza virus disease (e.g., influenza virus disease caused by an influenza B virus) a subject (e.g., ahuman), comprising sequentially administering to the subject two or more immunogenic compositions described herein, wherein one or more (e.g., two or more) of the immunogenic compositions comprises a mosaic HA, and wherein each mosaic HA is different from each other. In some embodiments, provided herein are methods of preventing influenza virus disease (e.g., influenza virus disease caused by an influenza B virus) a subject (e.g., a human), comprising sequentially administering to the subject two or more immunogenic compositions described herein, wherein one or more (e.g., two or more) of the immunogenic compositions comprises an inactivated or an inactivated split influenza B virus and a CpG oligonucleotide adjuvant described herein, wherein each inactivated or inactivated split influenza B virus comprises a mosaic HA, and wherein each mosaic HA is different from each other.

[0017] In another aspect, provided herein is an immunogenic composition comprising a mosaic HA described herein for use in combination with a CpG oligonucleotide adjuvant described herein for inducing an immune response (e.g., an immune response that is capable of cross-reacting with a plurality of influenza B virus strains and lineages) in a subject (e.g., human subject), immunizing a subject (e.g., a human) against influenza virus disease (e.g., influenza virus disease caused by an influenza B virus), or preventing influenza virus disease (e.g., influenza virus disease caused by an influenza B virus) a subject (e.g., a human). In some embodiments, provided herein is an immunogenic composition comprising an inactivated influenza virus (e.g., an inactivated influenza B virus) or an inactivated split influenza virus (e.g., an inactivated split influenza B virus) for use in combination with a CpG oligonucleotide adjuvant described herein for inducing an immune response (e.g., an immune response that is capable of cross-reacting with a plurality of influenza B virus strains and lineages) in a subject (e.g., human subject), immunizing a subject (e.g., a human) against influenza virus disease (e.g., influenza virus disease caused by an influenza B virus), or preventing influenza virus disease (e.g., influenza virus disease caused by an influenza B virus) a subject (e.g., a human), wherein the inactivated influenza virus or the inactivated split influenza B virus comprises a mosaic HA described herein. In some embodiments, the immunogenic composition further comprises an aluminum salt (e.g., amorphous aluminum hydroxyphosphate sulfate, aluminum hydroxide, aluminum phosphate, or potassium aluminum sulfate).

[0018] In some embodiments, provided herein are methods for inducing an immune response (e.g., an immune response that is capable of cross-reacting with a plurality of influenza B virus strains and lineages) in a subject (e.g., human subject), comprisingadministering an immunogenic composition comprising a mosaic HA described herein and administering a CpG oligonucleotide adjuvant described herein. In some embodiments, provided herein are methods for immunizing a subject (e.g., a human) against influenza virus disease (e.g., influenza virus disease caused by an influenza B virus), comprising administering an immunogenic composition comprising a mosaic HA described herein and administering a CpG oligonucleotide adjuvant described herein. In some embodiments, provided herein are methods for preventing influenza virus disease (e.g., influenza virus disease caused by an influenza B virus) a subject (e.g., a human), comprising administering an immunogenic composition comprising a mosaic HA described herein and administering a CpG oligonucleotide adjuvant described herein. In some embodiments, the immunogenic composition further comprises an aluminum salt (e.g., amorphous aluminum hydroxyphosphate sulfate, aluminum hydroxide, aluminum phosphate, or potassium aluminum sulfate).

[0019] In some embodiments, provided herein is the use of an immunogenic composition described herein in the manufacture of a medicament for use in combination with a CpG oligonucleotide adjuvant described herein for inducing an immune response (e.g., an immune response that is capable of cross-reacting with a plurality of influenza B virus strains and lineages) in a subject (e.g., human subject). In some embodiments, provided herein is the use of an immunogenic composition described herein in the manufacture of a medicament for use in combination with a CpG oligonucleotide adjuvant described herein for immunizing a subject (e.g., a human) against influenza virus disease (e.g., influenza virus disease caused by an influenza B virus). In some embodiments, provided herein is the use of an immunogenic composition described herein in the manufacture of a medicament for use in combination with a CpG oligonucleotide adjuvant described herein for preventing influenza virus disease (e.g., influenza virus disease caused by an influenza B virus) a subject (e.g., a human).

[0020] In another aspect, provided herein are kits. In some embodiments, provided herein are kits comprising a container containing an immunogenic composition described herein. In some embodiments, provided herein are kits comprising two or more containers, wherein each container contains a different immunogenic composition described herein. In some embodiments, provided herein are kits comprising two or more containers, wherein one container contains an immunogenic composition described herein and another container contains a CpG oligonucleotide adjuvant described herein. In some embodiments, provided herein are kits comprising two or more containers, wherein one container contains a mosaic HA and another container contains a CpG oligonucleotide adjuvant described herein. Insome embodiments, provided herein are kits comprising two or more containers, wherein one container contains an inactivated influenza B virus or an inactivated split influenza B virus, wherein the inactivated influenza B virus or the inactivated split influenza B virus comprises a mosaic HA, and another container contains a CpG oligonucleotide adjuvant described herein. In some embodiments, the kits comprise a container containing an aluminum salt (e.g., amorphous aluminum hydroxyphosphate sulfate, aluminum hydroxide, aluminum phosphate, or potassium aluminum sulfate).3.1 Terminology

[0021] As used herein, the term “about” or “approximately” when used in conjunction with a number refers to any number within 1%, 5%, or 10% of the referenced number and includes the referenced number.

[0022] The term “and / or” as used in a phrase such as “A and / or B” herein is intended to include both A and B; A or B; A (alone); and B (alone). Likewise, the term “and / or” as used in a phrase such as “A, B, and / or C” is intended to encompass each of the following embodiments: A, B, and C; A, B, or C; A or C; A or B; B or C; A and C; A and B; B and C; A (alone); B (alone); and C (alone).

[0023] The terms "mosaic influenza virus hemagglutinin," "mosaic influenza virus HA polypeptide," "mosaic hemagglutinin," " mosaic HA," "mosaic influenza hemagglutinin", “mosaic HA polypeptide”, and “mHA” are used herein interchangeably.

[0024] As used herein, the term “mHX / By” refers to a mosaic HA, wherein amino acid changes in one or more (e.g., 1, 2, 3, or 4) major antigenic sites of influenza B virus HA have been introduced based upon a corresponding influenza A virus HA sequence e.g.. an exotic avian A virus HA) and the X is the influenza A virus hemagglutinin subtype (e.g., H5, H8, Hl 1, or H13), and wherein BY refers to the influenza B virus HA (e.g., B / Yamanashi / 66 / 98 HA, B / Brisbane / 60 / 2008 HA, or B / Phuket / 3073 / 2013 HA) into which changes in the one or more antigenic sites have been introduced.

[0025] As used herein, the term "120 loop" refers to an antigenic site in an influenza B virus HA. In some embodiments, the term "120 loop" refers to amino acid residues 75 to 77, and 116 to 137 of the HA1 domain of influenza B virus B / Hong Kong / 8 / 73 HA or amino acid residues in the HA1 domain of an influenza B virus HA other than B / Hong Kong / 8 / 73 HA that correspond to amino acid residues 115 to 137 of the HA1 domain of influenza B virus B / Hong Kong / 8 / 73 HA (wherein the amino acid residues 75 to 77 and 116-137 correspond to the numbered positions of the influenza B virus B / Hong Kong / 8 / 73 HA not including thesignal peptide, i.e., the numbering of the mature HA). In some embodiments, the term "120 loop" refers to amino acid residues 75, 77, and 116 to 137 of the HA1 domain of influenza B virus B / Hong Kong / 8 / 73 HA or amino acid residues in the HA1 domain of an influenza B virus HA other than B / Hong Kong / 8 / 73 HA that correspond to amino acid residues 75, 77, and 116 to 137 of the HA1 domain of influenza B virus B / Hong Kong / 8 / 73 (wherein the amino acid residues 75, 77, and 116-137 correspond to the numbered positions of the influenza B virus B / Hong Kong / 8 / 73 HA not including the signal peptide, i.e., the numbering of the mature HA). In some embodiments, the term "120 loop" refers to amino acid residues 75, 77, 116, 118, 122, 129, and 137 of the HA 1 domain of influenza B virus B / Hong Kong / 8 / 73 HA or amino acid residues in the HA1 domain of an influenza B virus HA other than B / Hong Kong / 8 / 73 HA that correspond to amino acid residues 75, 77, 116, 118, 122, 129, and 137 of the HA1 domain of influenza B virus B / Hong Kong / 8 / 73 HA (wherein the amino acid residues 75, 77, 116, 118, 122, 129, and 137 correspond to the numbered positions of the influenza B virus B / Hong Kong / 8 / 73 HA not including the signal peptide, i.e., the numbering of the mature HA). In some embodiments, the term " 120 loop" refers to the antigenic site of an influenza B virus HA defined by Wang et al., 2008, Journal of Virology 82: 3011-3020 as the 120 loop or the equivalent thereof in other influenza B virus HAs. In some embodiments, the “120 loop” comprises the amino acid residues of influenza B / Yamagata / 16 / 1988 HA, B / Brisbane / 60 / 2008 HA, B / Phuket / 3073 / 2013 HA indicated in Table 3 for the 120 loop.

[0026] As used herein, the term "150 loop" refers to an antigenic site in an influenza B virus HA. In some embodiments, the term "150 loop" refers to amino acid residues 141 to 150 of the HA1 domain of influenza B virus B / Hong Kong / 8 / 73 HA or amino acid residues in the HA1 domain of an influenza B virus HA other than B / Hong Kong / 8 / 73 HA that correspond to amino acid residues 141 to 150 of the HA1 domain of influenza B virus B / Hong Kong / 8 / 73 HA (wherein the amino acid residues 141 to 150 correspond to the numbered positions of the influenza B virus B / Hong Kong / 8 / 73 HA not including the signal peptide, i.e., the numbering of the mature HA). In some embodiments, the term " 150 loop" refers to amino acid residues 141 and 144 to 150 of the HA1 domain of influenza B virus B / Hong Kong / 8 / 73 HA or amino acid residues in the HA1 domain of an influenza B virus HA other than B / Hong Kong / 8 / 73 HA that correspond to amino acid residues 141 and 144 to 150 of the HA1 domain of influenza B virus B / Hong Kong / 8 / 73 HA (wherein the amino acid residues 141 and 144 to 150 correspond to the numbered positions of the influenza B virus B / Hong Kong / 8 / 73 HA not including the signal peptide, i.e., the numbering of the matureHA). In some embodiments, the term " 150 loop" refers to the antigenic site of HA defined by Wang et al., 2008, Journal of Virology 82: 3011-3020 as the 150 loop or the equivalent thereof in other influenza B virus HAs. In some embodiments, the “150 loop” comprises the amino acid residues of influenza B / Yamagata / 16 / 1988 HA, B / Brisbane / 60 / 2008 HA, B / Phuket / 3073 / 2013 HA indicated in Table 3 for the 150 loop.

[0027] As used herein, the term "160 loop" refers to an antigenic site in an influenza B virus HA. In some embodiments, the term "160 loop" refers to amino acid residues 162 to 167 of the HA1 domain of influenza B virus B / Hong Kong / 8 / 73 HA or amino acid residues in the HA1 domain of an influenza B virus HA other than B / Hong Kong / 8 / 73 HA that correspond to amino acid residues 160 to 167 of the HA1 domain of influenza B virus B / Hong Kong / 8 / 73 HA (wherein the amino acid residues 162 to 167 correspond to the numbered positions of the influenza B virus B / Hong Kong / 8 / 73 HA not including the signal peptide, i.e., the numbering of the mature HA). In some embodiments, the term " 160 loop" refers to the antigenic site of HA defined by Wang et al., 2008, Journal of Virology 82: 3011- 3020 as the 160 loop or the equivalent thereof in other influenza B virus HAs. In some embodiments, the “160 loop” comprises the amino acid residues of influenza B / Yamagata / 16 / 1988 HA, B / Brisbane / 60 / 2008 HA, B / Phuket / 3073 / 2013 HA indicated in Table 3 for the 160 loop.

[0028] As used herein, the term "190 helix" refers to an antigenic site in an influenza B virus HA. In some embodiments, the term "190 helix" refers to amino acid residues 194 to 202 of the HA1 domain of influenza B virus B / Hong Kong / 8 / 73 HA or amino acid residues in the HA1 domain of an influenza B virus HA other than B / Hong Kong / 8 / 73 HA that correspond to amino acid residues 194 to 202 of the HA1 domain of influenza B virus B / Hong Kong / 8 / 73 HA (wherein the amino acid residues 194 to 202 correspond to the numbered positions of the influenza B virus B / Hong Kong / 8 / 73 HA not including the signal peptide, i.e., the numbering of the mature HA). In some embodiments, the term " 190 helix" refers to amino acid residues 194 to 200 of the HA1 domain of influenza B virus B / Hong Kong / 8 / 73 HA or amino acid residues in the HA1 domain of an influenza B virus HA other than B / Hong Kong / 8 / 73 HA that correspond to amino acid residues 194 to 200 of the HA1 domain of influenza B virus B / Hong Kong / 8 / 73 HA (wherein the amino acid residues 194 to 200 correspond to the numbered positions of the influenza B virus B / Hong Kong / 8 / 73 HA not including the signal peptide, i.e., the numbering of the mature HA). In some embodiments, the term "190 helix" refers to amino acid residues 194 to 200, 205 and 238 of the HA1 domain of influenza B virus B / Hong Kong / 8 / 73 HA or amino acid residues in theHA1 domain of an influenza B virus HA other than B / Hong Kong / 8 / 73 HA that correspond to amino acid residues 194 to 200, 205 and 238 of the HA1 domain of influenza B virus B / Hong Kong / 8 / 73 HA (wherein the amino acid residues 194 to 200, 205 and 238 correspond to the numbered positions of the influenza B virus B / Hong Kong / 8 / 73 HA not including the signal peptide, i.e., the numbering of the mature HA). In some embodiments, the term "190 helix" refers to amino acid residues 194 to 205 and 238 of the HA1 domain of influenza B virus B / Hong Kong / 8 / 73 HA or amino acid residues in the HA1 domain of an influenza B virus HA other than B / Hong Kong / 8 / 73 HA that correspond to amino acid residues 194 to 205 and 238 of the HA1 domain of influenza B virus B / Hong Kong / 8 / 73 (wherein the amino acid residues 194 to 205 and 238 correspond to the numbered positions of the influenza B virus B / Hong Kong / 8 / 73 HA not including the signal peptide, i.e., the numbering of the mature HA). In some embodiments, the term "190 helix" refers to the antigenic site defined by Wang et al., 2008, Journal of Virology 82: 3011-3020 as the 190 helix or the equivalent thereof in other influenza B virus HAs. In some embodiments, the “190 helix” comprises the amino acid residues of influenza B / Yamagata / 16 / 1988 HA, B / Brisbane / 60 / 2008 HA, B / Phuket / 3073 / 2013 HA indicated in Table 3 for the 190 helix.

[0029] In some embodiments, amino acid residues in an antigenic site (e.g., the 120 loop, 150 loop, 160 loop, and / or 190 helix) of an influenza B virus HA that correspond with amino acids in the same antigenic site e.g., the 120 loop, 150 loop, 160 loop, and / or 190 helix) of another influenza B virus HA may be determined by aligning the amino acid sequences of the two influenza B virus HAs. In some embodiments, the conformations / structures (e.g., the crystal structures) of the two influenza B virus HAs is considered.

[0030] As used herein, the terms “comprising” and “including” can be used interchangeably. The terms “comprising” and “including” are to be interpreted as specifying the presence of the stated features or components as referred to, but does not preclude the presence or addition of one or more features, or components, or groups thereof. Additionally, the terms “comprising” and “including” are intended to include examples encompassed by the term “consisting of’. Consequently, the term “consisting of’ can be used in place of the terms “comprising” and “including” to provide for more specific embodiments.

[0031] Conservative substitution" refers to replacement of an amino acid of one class is with another amino acid of the same class. In some embodiments, a conservative substitution does not alter the structure or function, or both, of a polypeptide. Classes of amino acids for the purposes of conservative substitution include hydrophobic (Met, Ala, Vai, Leu, He),neutral hydrophilic (Cys, Ser, Thr), acidic (Asp, Glu), basic (Asn, Gin, His, Lys, Arg), conformation disrupters (Gly, Pro) and aromatic (Trp, Tyr, Phe).

[0032] The terms “CpG,” “CpG motif,” and “cytosine-phosphate-guanosine,” as used herein, refer to an unmethylated cytidine-phospho-guanosine dinucleotide, which when present in an oligonucleotide contributes to a measurable immune response in vitro, in vivo and / or ex vivo. Examples of measurable immune responses include, but are not limited to, antigen-specific antibody production, secretion of cytokines, activation or expansion of lymphocyte populations, such as NK cells, CD4+ T lymphocytes, CD8+ T lymphocytes, B lymphocytes, and the like. Preferably, the CpG oligonucleotide preferentially activates a Th 1 -type response.

[0033] The term "ectodomain" in reference to an influenza virus HA would be understood by one of skill in the art. Generally, the ectodomain of an influenza virus HA comprises the globular head domain and stem domain. In specific embodiments, the ectodomain does not include the signal peptide of an influenza virus HA. See, e.g., Tables 1 and 3 below for exemplary influenza B virus HA ectodomain sequences (Table 1 also provides the location of the ectodomain). In some embodiments, the ectodomain of an influenza B virus HA is a region of the influenza B virus HA that aligns with the ectodomain of influenza B / Hong Kong / 8 / 73 virus HA ectodomain set forth in Tables 1 and 3, below. In some embodiments, the ectodomain of an influenza B virus HA is a region of the influenza B virus HA that aligns with the ectodomain of influenza B / Yamagata / 16 / 1988 virus HA ectodomain set forth in Table 3 below. In some embodiments, the ectodomain of an influenza B virus HA is a region of the influenza B virus HA that aligns with the ectodomain of influenza B / Brisbane / 60 / 2008 virus HA ectodomain set forth in Table 3 below. In some embodiments, the ectodomain of an influenza B virus HA is a region of the influenza B virus HA that aligns with the ectodomain of influenza B / Phuket / 3073 / 2013 virus HA ectodomain set forth in Table 3 below.

[0034] As used herein, the term “elderly human” refers to a human that is 65 years old or older.

[0035] As used herein, the terms "HA" and "hemagglutinin" refer to any influenza virus hemagglutinin known to those of skill in the art or a derivative thereof. Typically, a precursor influenza B virus hemagglutinin comprises domains including a signal peptide, a stem domain (or stalk domain), a globular head domain, a transmembrane domain, and a cytoplasmic domain. In some embodiments, a hemagglutinin consists of a single polypeptide chain, such as HAO. In some embodiments, a hemagglutinin consists of more than onepolypeptide chain in quaternary association, e.g., HA1 and HA2. Those of skill in the art will recognize that an immature HAO may be cleaved to release a signal peptide (generally approximately 15 to approximately 20 amino acids) to yield a mature hemagglutinin HAO (z.e., HAO without a signal peptide). In the context of an influenza B virus hemagglutinin, a mature hemagglutinin HAO is generally cleaved by proteolytic enzymes to yield an HA1 subunit (e.g., approximately 342 amino acids of influenza B / Hong Kong / 8 / 73 virus, including the globular head domain and a portion of the stem domain) and an HA2 subunit (e.g., approximately 169 amino acids of influenza B / Hong Kong / 8 / 73 virus, including the remainder of the stem domain, a transmembrane domain and a cytoplasmic domain). Those of skill in the art will recognize that an influenza B virus HA has an elongated fusion domain (composed of the central coiled-coil structure from the HA2 domain), the extended regions from HA1 (amino acid residues 1-42), and HA1 (amino acid residues 288-342), a globular membrane-distal domain containing the receptor-binding subdomain, HA1 (amino acid residues 116-274), and a vestigial esterase subdomain, HA1 (amino acid residues 43-115) and HA1 (amino acid residues 275-287) (see, e.g., Wang et al., 2008, Journal of Virology, 82(6):3011-3020). Those of skill in the art will recognize that the delineation of the domains of an influenza B virus HA may be determined from, e.g., crystal structure and / or by using structure prediction software (for example, the website for the Center for Biological Sequence Analysis, Technical University of Denmark DTU, or Pymol) in conjunction with protein alignments. Thus, in one aspect, one skilled in the art will recognize that the delineation of the domains of influenza B / Hong Kong / 8 / 73 virus HA are as set forth in Table 1, below. In some embodiments, the signal peptide of influenza B / Hong Kong / 8 / 73 virus HA comprises the amino acid sequence of SEQ ID NO: 74. In some embodiments, the transmembrane domain of influenza B / Hong Kong / 8 / 73 virus HA comprises the amino acid sequence of SEQ ID NO: 80. In some embodiments, the cytoplasmic domain of influenza B / Hong Kong / 8 / 73 virus HA virus HA comprises the amino acid sequence of SEQ ID NO: 81. In some embodiments, the globular head domain of influenza B / Hong Kong / 8 / 73 virus HA comprises the amino acid sequence of SEQ ID NO: 75. In some embodiments, the ectodomain of influenza B / Hong Kong / 8 / 73 virus HA comprises the amino acid sequence of SEQ ID NO: 76. In some embodiments, the stem domain of influenza B / Hong Kong / 8 / 73 virus HA comprises the amino acid sequence of SEQ ID NO: 78. In some embodiments, the HA1 domain of influenza B / Hong Kong / 8 / 73 virus HA virus HA comprises the amino acid sequence of SEQ ID NO: 79. In some embodiments, the HA2 domain of influenza B / Hong Kong / 8 / 73 virus HA virus HA comprises the amino acid sequence of SEQ ID NO: 90. Inanother aspect, one skilled in the art will recognize the delineation of domains of the influenza B / Yamagata / 16 / 1988 virus HA. See, e.g., Table 3, infra, for exemplary domains for the influenza B / Yamagata / 16 / 1988 virus HA. In some embodiments, the signal peptide of influenza B / Yamagata / 16 / 1988 virus HA comprises the amino acid sequence of SEQ ID NO: 50. In some embodiments, the transmembrane domain of influenza B / Yamagata / 16 / 1988 virus HA comprises the amino acid sequence of SEQ ID NO: 51. In some embodiments, the cytoplasmic domain of influenza B / Yamagata / 16 / 1988 virus HA comprises the amino acid sequence of SEQ ID NO: 52. In some embodiments, the globular head domain of influenza B / Yamagata / 16 / 1988 virus HA comprises the amino acid sequence of SEQ ID NO: 53. In some embodiments, the ectodomain of influenza B / Yamagata / 16 / 1988 virus HA comprises the amino acid sequence of SEQ ID NO: 54. In some embodiments, the stem domain of influenza B / Yamagata / 16 / 1988 virus HA comprises the amino acid sequences of SEQ ID NOs: 55 and 94. In some embodiments, the HA1 domain of influenza B / Yamagata / 16 / 1988 virus HA comprises the amino acid sequence of SEQ ID NO: 56. In some embodiments, the HA2 domain of influenza B / Yamagata / 16 / 1988 virus HA comprises the amino acid sequence of SEQ ID NO: 57. In another aspect, one skilled in the art will recognize the delineation of domains of the influenza B / Brisbane / 60 / 2008 virus HA. See, e.g., Table 3, infra, for exemplary domains of the influenza B / Brisbane / 60 / 2008 virus HA. In some embodiments, the signal peptide of influenza B / Brisbane / 60 / 2008 virus HA comprises the amino acid sequence of SEQ ID NO: 58. In some embodiments, the transmembrane domain of influenza B / Brisbane / 60 / 2008 virus HA comprises the amino acid sequence of SEQ ID NO: 59. In some embodiments, the cytoplasmic domain of influenza B / Brisbane / 60 / 2008 virus HA comprises the amino acid sequence of SEQ ID NO: 60. In some embodiments, the globular head domain of influenza B / Brisbane / 60 / 2008 virus HA comprises the amino acid sequence of SEQ ID NO: 61. In some embodiments, the ectodomain of influenza B / Brisbane / 60 / 2008 virus HA comprises the amino acid sequence of SEQ ID NO: 62. In some embodiments, the stem domain of influenza B / Brisbane / 60 / 2008 virus HA comprises the amino acid sequences of SEQ ID NOs: 63 and 95. In some embodiments, the HA1 domain of influenza B / Brisbane / 60 / 2008 virus HA comprises the amino acid sequence of SEQ ID NO: 64. In some embodiments, the HA2 domain of influenza B / Brisbane / 60 / 2008 virus HA comprises the amino acid sequence of SEQ ID NO: 65. In another aspect, one skilled in the art will recognize the delineation of domains of the influenza B / Phuket / 3073 / 2013 virus HA. See, e.g., Table 3, infra, for exemplary domains of the influenza B / Phuket / 3073 / 2013 virus HA. In some embodiments, the signal peptide of influenza B / Phuket / 3073 / 2013 virus HA comprisesthe amino acid sequence of SEQ ID NO: 66. In some embodiments, the transmembrane domain of influenza B / Phuket / 3073 / 2013 virus HA comprises the amino acid sequence of SEQ ID NO: 67. In some embodiments, the cytoplasmic domain of influenzaB / Phuket / 3073 / 2013 virus HA virus HA comprises the amino acid sequence of SEQ ID NO: 68. In some embodiments, the globular head domain of influenza B / Phuket / 3073 / 2013 virus HA virus HA comprises the amino acid sequence of SEQ ID NO: 69. In some embodiments, the ectodomain of influenza B / Phuket / 3073 / 2013 virus HA virus HA comprises the amino acid sequence of SEQ ID NO: 70. In some embodiments, the stem domain of influenza B / Phuket / 3073 / 2013 virus HA virus HA comprises the amino acid sequences of SEQ ID NOs: 71 and 96. In some embodiments, the HA1 domain of influenza B / Phuket / 3073 / 2013 virus HA virus HA comprises the amino acid sequence of SEQ ID NO: 72. In some embodiments, the HA2 domain of influenza B / Phuket / 3073 / 2013 virus HA virus HA comprises the amino acid sequence of SEQ ID NO: 73.

[0036] Table 1. Exemplary domains for influenza B / Hong Kong / 8 / 73 virus HA.Abbreviations: nt= nucleotide; aa=amino acid; N / A=not applicable.

[0037] In some embodiments, a hemagglutinin protein comprises a signal peptide, an ectodomain, a transmembrane domain and a cytoplasmic domain. In some embodiments, a hemagglutinin lacks a signal peptide, ie., the hemagglutinin is a mature hemagglutinin. In some embodiments, a hemagglutinin protein comprises an ectodomain, a transmembrane domain and a cytoplasmic domain. In some embodiments, a hemagglutinin lacks a transmembrane domain or cytoplasmic domain, or both. In some embodiments, a hemagglutinin protein comprises an HA ectodomain.

[0038] The terms "hemagglutinin" and "HA" in the context of influenza virus, as used herein, encompass an influenza virus HA monomer as well as trimers of influenza virus HA. In addition, the terms "hemagglutinin" and "HA", as used herein, encompass influenza virus hemagglutinin that are modified by, e.g., glycosylation (e.g., N-linked glycosylation) and lipid modification (e.g., S-palmitoylation).

[0039] The terms “influenza virus globular head domain”, “influenza virus HA globular head domain”, “influenza HA globular head domain”, “globular head domain”, “head domain”, “HA head domain”, “HA globular head”, and “HA globular head domain” are used herein interchangeably to refer to the globular head domain of an influenza hemagglutininpolypeptide. An influenza virus hemagglutinin head domain polypeptide or influenza virus hemagglutinin head domain may comprise or consist of a known (e.g., wild-type) influenza virus hemagglutinin head domain or may comprise or consist of a derivative, e.g., an engineered derivative, of a known (e.g., wild-type) influenza virus hemagglutinin head domain. Those of skill in the art will recognize that an influenza B virus HA globular head domain typically comprises the amino acid residues corresponding to amino acid residues 43- 289 of the HA1 domain of influenza B / Hong Kong / 8 / 73 virus (wherein the numbering of the amino acid residues is with respect to the mature HA sequence, which does not comprise the 15 amino acid signal peptide). For example, one skilled in the art will recognize that the amino acid sequence for the HA globular head domain for influenza B / Hong Kong / 8 / 73 virus typically consists of the amino acid sequence set forth in Table 1 above. Those of skill in the art will recognize that the location of the influenza B virus HA globular head domain for a particular strain can be determined by alignment of the influenza B virus HA polypeptide for said strain to the sequence of other influenza A virus HA. In some embodiments, the influenza B virus HA globular head domain consists of the amino acid residues that align to amino acid residues 58-304 of the mature influenza B / Hong Kong / 8 / 73 virus HA (z.e., wherein said numbering includes the signal peptide). See, e.g., Tables 1 and 3, for exemplary HA globular head domains.

[0040] The terms “influenza virus stem domain”, “influenza stem domain”, “influenza HA stem domain”, “stem domain”, “stalk domain”, ’’influenza virus HA stem domain”, “HA stalk”, “HA stalk domain”, and “HA stem domain” are used herein interchangeably to the stem domain of an influenza virus HA known to one of skill in the art. Typically, the stem domain of an influenza virus HA consists of an N-terminal portion of the HA1 domain, a C- terminal portion of the HA1 domain, and a portion of the HA2 domain. See, e.g., Tables 1 and 3 for exemplary stem domains. For example, the stem domain of influenza B / Yamagata / 16 / 1988 virus HA comprises the amino acid sequences SEQ ID NOs: 55 and 94. SEQ ID NO: 55 provides the amino acid sequence of the N-terminal portion of the HA1 domain of influenza B / Yamagata / 16 / 1988 virus HA that is part of the influenza B / Yamagata / 16 / 1988 virus HA stem domain. SEQ ID NO: 94 includes the amino acid sequence of the C-terminal portion of the HA1 domain of influenza B / Yamagata / 16 / 1988 virus HA that is part of the influenza B / Yamagata / 16 / 1988 virus HA stem domain and the amino acid sequence of the HA2 stem domain of influenza B / Yamagata / 16 / 1988 virus HA. In another example, the stem domain of influenza B / Brisbane / 60 / 2008 virus HA comprises the amino acid sequences of SEQ ID NOs: 63 and 95. SEQ ID NO: 63 provides the aminoacid sequence of the N-terminal portion of the HA1 domain of influenza B / Brisbane / 60 / 2008 virus HA that is part of the influenza B / Brisbane / 60 / 2008 virus HA stem domain. SEQ ID NO: 95 includes the amino acid sequence of the C-terminal portion of the HA1 domain of influenza B / Brisbane / 60 / 2008 virus HA that is part of the influenza B / Brisbane / 60 / 2008 virus HA stem domain and the amino acid sequence of the HA2 stem domain of influenza B / Brisbane / 60 / 2008 virus HA. In another example, the stem domain of influenza B / Phuket / 3073 / 2013 virus HA comprises the amino acid sequence of SEQ ID NOs: 71 and 96. SEQ ID NO: 71 provides the amino acid sequence of the N-terminal portion of the HA1 domain of influenza B / Phuket / 3073 / 2013 virus HA that is part of the influenza B / Phuket / 3073 / 2013 virus HA stem domain. SEQ ID NO: 96 includes the amino acid sequence of the C-terminal portion of the HA1 domain of influenza B / Phuket / 3073 / 2013 virus HA that is part of the influenza B / Phuket / 3073 / 2013 virus HA stem domain and the amino acid sequence of the HA2 stem domain of influenza B / Phuket / 3073 / 2013 virus HA.

[0041] As used herein, the term “HA1” refers to the HA1 of an influenza virus hemagglutinin. Typically, an HA1 includes the globular head domain and a portion of the stem domain of influenza virus hemagglutinin (see, e.g., Sriwilaijaroen and Suzuki, Proc Jpn Acad Ser B Phys Biol Sci. 2012 Jun 11; 88(6): 226-249, the contents of which is incorporated by reference in its entirety). See, e.g., Tables 1 and 3 for exemplary HA1 domains.

[0042] As used herein, the term “HA2" refers to the HA2 of an influenza virus hemagglutinin. Typically, an HA2 includes a portion of the stem domain, a transmembrane domain, and a cytoplasmic domain of influenza virus hemagglutinin (see, e.g., Sriwilaijaroen and Suzuki, Proc Jpn Acad Ser B Phys Biol Sci. 2012 Jun 11; 88(6): 226-249, the contents of which is incorporated by reference in its entirety). In some embodiments, an HA2 consists of amino acid residues 1-169 of the HA2 domain of an influenza B / Hong Kong / 8 / 73 virus (see, e.g., Wang et al., 2008, Journal of Virology 82: 3011-3020). See, e.g., Tables 1 and 3 for exemplary HA2 domains.

[0043] As used herein, the terms “HA2 stem domain” and “HA2 stalk domain” refers to the stem domain of the HA2 domain of an influenza virus hemagglutinin.

[0044] As used herein, the term "heterologous" in the context of a polypeptide, nucleic acid or virus refers to a polypeptide, nucleic acid or virus, respectively, that is not normally found in nature or not normally associated in nature with a polypeptide, nucleic acid or virus of interest. In specific embodiments a heterologous polypeptide, nucleic acid, or virus has been engineered or altered by the hand of man.

[0045] As used herein, the term “human adult” refers to a human 18 years old and older.

[0046] As used herein, the term “human child” refers to a human 1 years old to 18 years old.

[0047] As used herein, the term “human infant” refers to a newborn human to 1 years old.

[0048] As used herein, the term “nucleic acid” and “nucleotide” is intended to includeDNA molecules (e.g., cDNA or genomic DNA) and RNA molecules (e.g., mRNA) and analogs of the DNA or RNA generated using nucleotide or nucleoside analogs. In specific embodiments, the nucleic acid is a negative-sense single stranded RNA. In some embodiments, the nucleic acid is cDNA.

[0049] As used herein, the term “or” is to be interpreted as an inclusive “or” meaning any one or any combination. Therefore, “A, B or C” means any of the following: “A; B; C; A and B; A and C; B and C; A, B and C”. An exception to this definition will occur only when a combination of elements, functions, steps or acts are in some way inherently mutually exclusive.

[0050] Percent identity: Techniques known to one of skill in the art can be used to determine the percent identity between two amino acid sequences or between two nucleotide sequences. Generally, to determine the percent identity of two amino acid sequences or of two nucleic acid sequences, the sequences are aligned for optimal comparison purposes (e.g., gaps can be introduced in the sequence of a first amino acid or nucleic acid sequence for optimal alignment with a second amino acid or nucleic acid sequence). The amino acid residues or nucleotides at corresponding amino acid positions or nucleotide positions are then compared. When a position in the first sequence is occupied by the same amino acid residue or nucleotide as the corresponding position in the second sequence, then the molecules are identical at that position. The percent identity between the two sequences is a function of the number of identical positions shared by the sequences (z.e., % identity = number of identical overlapping positions / total number of positions X 100%). In some embodiments, the two sequences are the same length. In some embodiments, the percent identity is determined over the entire length of an amino acid sequence or nucleotide sequence. The determination of percent identity between two sequences (e.g., amino acid sequences or nucleic acid sequences) can also be accomplished using a mathematical algorithm. A nonlimiting example of a mathematical algorithm utilized for the comparison of two sequences is the algorithm of Karlin and Altschul, 1990, Proc. Natl. Acad. Sci. U.S.A.87:22642268, modified as in Karlin and Altschul, 1993, Proc. Natl. Acad. Sci. U.S.A.90:58735877. Such analgorithm is incorporated into the NBLAST and XBLAST programs of Altschul et al., 1990,J. Mol. Biol.215:403.

[0051] BLAST nucleotide searches can be performed with the NBLAST nucleotide program parameters set, e.g., for score=100, wordlength=12 to obtain nucleotide sequences homologous to nucleic acid molecules described herein. BLAST protein searches can be performed with the XBLAST program parameters set, e.g., to score 50, wordlength=3 to obtain amino acid sequences homologous to a protein molecule described herein. To obtain gapped alignments for comparison purposes, Gapped BLAST can be utilized as described in Altschul et al., 1997, Nucleic Acids Res.25:33893402. Alternatively, PSI BLAST can be used to perform an iterated search which detects distant relationships between molecules (Id). When utilizing BLAST, Gapped BLAST, and PSI Blast programs, the default parameters of the respective programs (e.g., of XBLAST and NBLAST) can be used (see, e.g., National Center for Biotechnology Information (NCBI) on the worldwide web, ncbi.nlm.nih.gov). In another non-limiting example of a mathematical algorithm utilized for the comparison of sequences is the algorithm of Myers and Miller, 1988, CABIOS 4: 1117. Such an algorithm is incorporated in the ALIGN program (version 2.0) which is part of the GCG sequence alignment software package. When utilizing the ALIGN program for comparing amino acid sequences, a PAM 120 weight residue table, a gap length penalty of 12, and a gap penalty of 4 can be used. The percent identity between two sequences can be determined using techniques similar to those described above, with or without allowing gaps. In calculating percent identity, typically only exact matches are counted.

[0052] As used interchangeably herein, the terms “polynucleotide” and “oligonucleotide” are oligomers of nucleic acids and include single-stranded DNA (ssDNA), double-stranded DNA (dsDNA), single-stranded RNA (ssRNA) and double-stranded RNA (dsRNA), modified oligonucleotides and oligonucleosides or combinations thereof. The oligonucleotide can be linearly or circularly configured, or the oligonucleotide can contain both linear and circular segments. Oligonucleotides are polymers of nucleosides joined, generally, through phosphodiester linkages, although alternate linkages, such as phosphorothioate esters may also be used in oligonucleotides. A nucleoside consists of a purine (adenine (A) or guanine (G) or derivative thereof) or pyrimidine (thymine (T), cytosine (C) or uracil (U), or derivative thereof) base bonded to a sugar. The four nucleoside units (or bases) in DNA are called deoxyadenosine, deoxyguanosine, thymidine, and deoxy cytidine.

[0053] As used herein, the terms “purified” and “isolated” when used in the context of a polypeptide (including an antibody) that is obtained from a natural source, e.g., cells, refers to a polypeptide which is substantially free of contaminating materials from the natural source, e.g., minerals, chemicals from the environment, and / or cellular materials from the natural source, such as but not limited to cell debris, cell wall materials, membranes, organelles, the bulk of the nucleic acids, carbohydrates, proteins, and / or lipids present in cells. Thus, a polypeptide that is isolated includes preparations of a polypeptide having less than about 30%, 20%, 10%, 5%, 2%, or 1% (by dry weight) of cellular materials and / or contaminating materials. As used herein, the terms “purified” and “isolated” when used in the context of a polypeptide (including an antibody) that is chemically synthesized refers to a polypeptide which is substantially free of chemical precursors or other chemicals which are involved in the syntheses of the polypeptide. A polypeptide that is chemically synthesized contains less than about 30%, 20%, 10%, 5%, 2%, or 1% of chemical precursors or other chemicals used in the synthesis of the polypeptide. In a specific embodiment, a mosaic B is chemically synthesized. In another specific embodiment, a mosaic B is isolated.

[0054] As used herein, the terms "replication," "viral replication" and "virus replication" in the context of a virus refer to one or more, or all, of the stages of a viral life cycle which result in the propagation of virus. The steps of a viral life cycle include, but are not limited to, virus attachment to the host cell surface, penetration or entry of the host cell (e.g., through receptor mediated endocytosis or membrane fusion), uncoating (the process whereby the viral capsid is removed and degraded by viral enzymes or host enzymes thus releasing the viral genomic nucleic acid), genome replication, synthesis of viral messenger RNA (mRNA), viral protein synthesis, and assembly of viral ribonucleoprotein complexes for genome replication, assembly of virus particles, post-translational modification of the viral proteins, and release from the host cell by lysis or budding and acquisition of a phospholipid envelope which contains embedded viral glycoproteins. In some embodiments, the terms "replication," "viral replication" and "virus replication" refer to the replication of the viral genome. In some embodiments, the terms "replication," "viral replication" and "virus replication" refer to the synthesis of viral proteins.

[0055] As used herein, terms “subject” or “patient” are used interchangeably to refer to an animal (e.g., birds, reptiles, and mammals). In some embodiments, a subject is a bird. In some embodiments, a subject is a mammal including a non-primate (e.g., a camel, donkey, zebra, cow, pig, horse, goat, sheep, cat, dog, rat, and mouse) and a primate (e.g. , a monkey, chimpanzee, and a human). In some embodiments, a subject is a non-human animal. Insome embodiments, a subject is a farm animal or pet. In specific embodiments, a subject is a human. In some embodiments, a subject is a human adult. In some embodiments, a subject is an elderly human. In some embodiments, a subject is a human child. In some embodiments, a subject is a human infant.

[0056] As used herein, the term “seasonal influenza virus strain” refers to a strain of influenza virus to which a subject population is exposed to on a seasonal basis. In specific embodiments, the term seasonal influenza virus strain refers to a strain of influenza B virus.

[0057] The terms “tertiary structure” and “quaternary structure” have the meanings understood by those of skill in the art. Tertiary structure refers to the three-dimensional structure of a single polypeptide chain. Quaternary structure refers to the three dimensional structure of a polypeptide having multiple polypeptide chains.

[0058] In some embodiments, the phrase “wild-type” in the context of a viral polypeptide refers to a viral polypeptide that is found in nature and is associated with a naturally occurring virus.

[0059] In some embodiments, the phrase “wild-type” in the context of a virus refers to a virus that is prevalent, circulating naturally and producing typical outbreaks of disease. In some embodiments, the term “wild-type” in the context of a virus refers to a parental virus.4. DESCRIPTION OF THE FIGURES

[0060] FIGS. 1A-1H depict influenza B virus surveillance and universal influenza vaccine design. FIG. 1A depicts surveillance of influenza B viruses in the US from 1997 to 2023. FIG. IB depicts the percentage of influenza B B / Yamagata / 16 / 1988-like and B / Victoria / 2 / 1987-like lineage identified viruses from 2015 to 2023 (Data taken from FluNet, (who.int) as of 1st Aug 2023). FIG. 1C depicts a phylogenetic tree of HA sequences of historical annual formulations for IBV vaccine strains from 1999 to 2023 (Data taken from Global Influenza Programme (who.int) as of 1st Aug 2023 and reported in FIGS. 1G-1H). Influenza B virus HA sequences used in this study were from B / Yamagata / 16 / 1988 as prime vaccination and from B / Brisbane / 60 / 2008 and B / Phuket / 3073 / 2013 as universal influenza vaccines. The phylogenetic tree was constructed using the maximum likelihood method and Tamura-Nei model and was visualized through Megal 1 (Tamura et al, 2021, Mol Biol Evol. 38:3022-3027; Tamura and Nei, 1993, Mol Biol Evol 10:512-26). FIG. ID depicts mosaic HA (mHA) universal influenza vaccine approach. Sequential vaccination with mHA vaccines, where the major immunodominant epitopes were replaced in each vaccination, would redirect the immune response towards subdominant head and stalk epitopes of the HAglycoprotein (PDB accession no. 4M44). FIG. IE depicts the mHA influenza B virus rescue scheme. B mHA and wildtype (WT) viruses were rescued following the reverse genetics method as previously described (Sun et al., 2019, J Virol 93). Thereafter, viruses were propagated in embryonated chicken eggs, and the viruses were harvested in the allantoic fluid. The mosaic viruses were based on the B / Yamagata / 16 / 1988 (Yam), B / Brisbane / 60 / 2008 (Bris) and B / Phuket / 3073 / 2013 (Phu), to generate the mH8 / BYam, mH13 / BBris and mH5 / Bphu viruses, respectively (Liu et al., 2021, Front Immunol 12:746447). FIG. IF depicts mHA influenza B vaccine preparation. Whole inactivated viruses (WIV) were generated by inactivating the harvested products with either formaldehyde (FA) or betapropiolactone (BPL) and purified by sucrose cushion ultracentrifugation. To produce split versions of these vaccines, BPL inactivated, and purified virus preparations were treated with Triton-XlOO and the remaining detergent was then removed using hydrophobic beads in batch mode chromatography (Puente-Massaguer et al., 2023, Front Bioeng Biotechnol 11 : 1097349). FIGS. 1G-1H depict phylogenetic sequences of historical annual formulation of influenza B vaccines of FIG. 1C. FIG. 1G depicts IBV HA sequences of historical annual formulation for IBV vaccine strains from 1999 to 2023 used to construct the phylogenetic tree using the maximum likelihood method and Tamura-Nei model and was visualized through Megal 1 (Tamura et al, 2021, Mol Biol Evol. 38:3022-3027; Tamura and Nei, 1993, Mol Biol Evol 10:512-526). FIG. 1H depicts historical annual formulation for IBV vaccine strains from 1999 to 2023 (Global Influenza Programme (who.int) as of 1st Aug 2023).

[0061] FIGS. 2A-2K show comparison of the antibody responses elicited by wildtype and mHA vaccines prepared by three different methods, and protection of mHA inactivated vaccines by three different preparation methods of FIGS. 2A-2F. Two different preparation methods for whole inactivated virus with formaldehyde (FA) or beta-propiolactone (BPL) and one split inactivated vaccine combining BPL inactivation and Triton-XlOO splitting were compared for two different vaccinations with WT viruses or mHA viruses. Vaccines were tested without adjuvant or with the addition of CpG 1018® (30 pg). FIGS. 2A-2F show comparison of the antibody responses elicited by wildtype and mHA vaccines prepared by three different methods. FIGS. 2A-2B depict vaccination regimen and groups. BALB / c mice (n = 10) were vaccinated in a three-dose vaccination experiment with a dose of 1 pg of HA in a 3-4 week interval. mHA split inactivated adjuvanted with AddaVax™ (1 : 1 v:v) and unvaccinated group (PBS) were included as controls. FIG. 2C depicts binding of serum antibodies towards the immuno-subdominant epitopes. A cH7 / Byam protein with a group 2 avian H7 head and the B / Yamagata / 16 / 1988 HA stalk was used to measure stalk-specificantibodies. A mHl 1 / Byam protein displaying the Hl 1 sequences at the major antigenic sites within the B / Yamagata / 16 / 1988 HA was used to measure antibody binding to conserved epitopes in the head and stalk domains. The geometric mean endpoint titer was calculated as the readout. The statistics were calculated using unpaired one-tailed t test (*P < 0.05; **P < 0.01; ***p < 0.001; ****P<0.0001). FIG. 2D shows heatmap of binding serum antibodies against a panel of recombinant influenza B HA proteins. The geometric mean area under the curve (AUC) of each group measured by triplicate pool is depicted. FIG. 2E shows heatmap of hemagglutination inhibition (HI) titer against a panel of influenza B viruses. Mean HI titer of each group measured by triplicate pool is depicted. FIG. 2F shows heatmap of ADCC activity against three influenza B viruses. To perform the ADCC reporter assay, MDCK cells were infected with each virus at an MOI of 5 with single-cycle replication. The AUC of fold induction of each group measured by triplicate pool is depicted. FIGS. 2G-2K show protection of mHA inactivated vaccines by three different preparation methods of FIGS. 2A- 2F. Passive transfer was performed against B / Lee / 40, B / New York / PVOl 181 / 2018 (Victorialineage), and B / New York / PV00094 / 2017 (Yamagata-lineage). FIGS. 2G-2J depict weight loss and survival of vaccination groups challenged with virus. BALB / c mice (n = 5) received 100 pL of pooled sera intraperitoneally and 2 hours later were challenged intranasally with 5 mLD50 of challenge virus in a total volume of 30 pL. Weight loss and survival of mice were monitored for 2 weeks with a humane endpoint of >25% loss of the initial weight. In the survival plots, the proportion of surviving animals in each group is shown. FIG. 2K shows minimum weight reported during the passive transfer experiment. Mean ± SD for each group and statistical significance inferred by Kruskal-Wallis test corrected using Dunn’s test for multiple comparisons against PBS group is depicted (*P < 0.05; **P < 0.01; ***p < 0.001).

[0062] FIGS. 3A-3O show Thl / Th2 immunogenicity and protection of mHA vaccines in a low pre-existing immunity model. FIG. 3A depicts the vaccination regimen and experimental workflow. FIG. 3B shows the vaccination groups. BALB / c mice (n = 5) were vaccinated in a two-dose vaccination after low priming with 1 pg of mH8 / BYam protein with a dose of 1 pg of HA of the different vaccines in a 3-4 week interval. WIV or split mHA vaccines were tested without adjuvant or with the addition of CpG 1018® (30 pg) or AddaVax™ (1 : 1 v:v). A QIV (Flulaval Quadrivalent) vaccinated group and an unvaccinated group (PBS) were included as controls. FIGS. 3C-3E show binding of serum antibody titers against subdominant and cross-reactive epitopes as previously described in FIGS. 1A-1H and FIGS. 2G-2K. Binding IgG2a / IgGl ratio (FIG. 3F), IgGl (FIG. 3G) and IgG2a (FIG. 3H) serum antibody titers against B / Lee / 40 HA recombinant protein are shown. FIG. 31 depictsfrequency of germinal center B cells. Inguinal lymph nodes were collected 4 weeks after second boost and frequency of germinal center B cells (live CD3'B220+CD19+IgD' GL7+CD38low) was measured by FACS. Kruskal-Wallis test corrected using Dunn’s test for multiple comparisons is depicted in these graphs (*P < 0.05; **P < 0.01; ***p < 0.001; ****p<0.0001). Direct challenge (FIGS. 3J-3L) and passive transfer challenge (FIGS. 3M- 30) with 5 mLD50 of B / Lee / 40 virus are depicted. Weight loss (FIGS. 3 J, 3M), survival of vaccination groups (FIGS. 3K, 3N) and minimum weight (FIGS. 3L, 30) were reported for each experiment. For direct challenge, BALB / c mice (n=5) were challenge 4 weeks after second boost intranasally (IN) in a total volume of 30 pL. In passive transfer, BALB / c mice (n = 5) received 100 pL of pooled sera intraperitoneally and 2 hours later were challenged IN as previously described. Weight loss and survival of mice were monitored for 2 weeks with a humane endpoint of >25% loss of the initial weight. Mean minimum weight ± SD for each group and statistical significance inferred by Kruskal -Wallis test corrected using Dunn’s test for multiple comparisons against PBS group is depicted (*P < 0.05; **P < 0.01; ***p < 0.001).

[0063] FIGS. 4A-4L show Thl / Th2 immunogenicity of mHA vaccines in a high preexisting immunity model in mice. FIG. 4A depicts vaccination regimen and experimental workflow. FIG. 4B shows the vaccination groups. BALB / c mice (n = 10) were vaccinated in a two-dose vaccination of 1 pg of HA of the different WIV or split mHA vaccines in a 3-4 week interval after high priming with 105PFU of mH8 / BYam virus. WIV and split mHA vaccines were tested without adjuvant or with the addition of CpG 1018® (30 pg) or AddaVax™ (1 : 1 v:v). A QIV (Flulaval Quadrivalent) vaccinated group and an unvaccinated group (PBS) were included as controls. mH8 / BYam virus infection was given intranasally in a total volume of 30 pL. FIG. 4C depicts heatmap of Thl / Th2 cytokine panel measured in sera taken 4 hours after second boost vaccination using a 11-plex Luminex panel. Log2 foldchange over PBS group and 2-way ANOVA test corrected using Dunnet’s test for multiple comparisons is depicted (*P < 0.05; **P < 0.01; ***p < 0.001). FIGS. 4D-4E show binding of serum antibody titers against subdominant epitopes analyzed as previously described in FIGS. 3A-3O. Minimum weight loss of direct challenge against ancestral B / Lee / 40 (F), B / New York / PV01181 / 2018 (Victoria-lineage) (FIG. 4G) and B / New York / PV00094 / 2017 (Yamagata-lineage) (FIG. 4H) were shown. FIG. 41 depicts frequency of germinal center B cells. Inguinal lymph nodes were collected 4 weeks after second boost and frequency of germinal center B cells (live CD3 B220+CD19+IgD GL7+CD38low) was measured by FACS. Passive transfer challenge with B / Lee / 40 virus (FIGS. 4J-4L) weightloss (FIG. 4J), survival of vaccination groups (FIG. 4K) and minimum weight loss (FIG. 4L) was reported. For direct challenge, BALB / c mice (n=5) were challenged 4 weeks after second boost intranasally (IN) in a total volume of 30 pL. In passive transfer, BALB / c mice (n = 5) received 100 pL of pooled sera intraperitoneally and 2 hours later were challenged IN as previously described. In all cases a dose of 5 mLD50 was used. Weight loss and survival of mice were monitored for 2 weeks with a humane endpoint of >25% loss of the initial weight. Statistical significance inferred by Kruskal-Wallis test corrected using Dunn’s test for multiple comparisons against PBS group is depicted (*P < 0.05; **P < 0.01; ***p < 0.001).

[0064] FIGS. 5A-5H show optimization of influenza B priming vaccination in mice models. FIG. 5A shows the vaccination regimen. BALB / c mice (n = 5) were vaccinated in a two-dose vaccination experiment in a 3-4 week interval with the different prime vaccinations. FIGS. 5B-5G show binding of serum antibodies towards the immuno-subdominant epitopes and B / Lee / 40 HA-specific binding antibody titers as a surrogate of cross-reactive antibodies measured as previously described in FIGS. 1A-1F. Statistical significance inferred by Kruskal -Wallis test corrected using Dunn’s test for multiple comparisons against PBS group is depicted (*P < 0.05; **P < 0.01; ***p < 0.001). FIG. 5H depicts weight loss of passive transfer of mH8 / Byam priming with a 5 LD50 dose. BALB / c mice (n = 5) received 100 pL of pooled sera intraperitoneally and were challenged intranasally with 5 mLD50 or 50LD50 of challenge virus. Weight loss and survival of mice were monitored for 2 weeks with a humane endpoint of >25% loss of the initial weight.

[0065] FIGS. 6A-6F show T cell immunity after mHA vaccine measured by intracellular cytokine staining. BALB / c mice (n = 5) were vaccinated in a two-dose vaccination after low priming with 1 pg of rnHS / Byam protein with a dose of 1 pg of HA of the different vaccines in a 3-4 week interval. WIV or split mHA vaccines were tested without adjuvant or with the addition of CpG 1018® (30 pg) or AddaVax™ (1 : 1 v:v). A QIV (Flulaval Quadrivalent) vaccinated group and an unvaccinated group (PBS) were included as controls. Functional T cell analysis by intracellular cytokine staining was depicted (FIGS. 6A-6D). One week after the last boost, mice were euthanized and splenocytes were harvested. Splenocytes were ex- vivo stimulated with HA, NP or Ml peptide pool and intracellular cytokine staining was performed and analyzed by FACS. Intracellular cytokine staining was used to measure antigen-specific production of IFN-y, TNF-a and IL-2, by CD4+ (FIGS. 6A, 6C, 6E) or CD8+ T cells (FIGS. 6B, 6D, 6F). Log2 foldchange over PBS group and two-way ANOVAfor each profile against the naive group and corrected for Dunnett’s multiple comparisons test are depicted (*p < 0.05; **p < 0.01; ***p < 0.001; ****p < 0.0001).

[0066] FIGS. 7A-7D show that T cell immunity after mHA vaccine measured by intracellular cytokine staining BALB / c mice (n = 5) were vaccinated in a two-dose vaccination after high priming with 1 x 105PFU of mH8 / BYam virus with a dose of 1 pg of HA of the different vaccines in a 3-4 week interval. WIV or split mHA vaccines were tested without adjuvant or with the addition of CpG 1018® (30 pg) or AddaVax™ (1 : 1 v:v). A QIV (Flulaval Quadrivalent) vaccinated group and an unvaccinated group (PBS) were included as controls. FIGS. 7A-7D show functional T cell analysis by intracellular cytokine staining. One week after the last boost, mice where euthanized and spleenocytes were harvested. Splenocytes were ex-vivo stimulated with HA, NP or Ml peptide pool and intracellular cytokine staining was performed and analyzed by FACS. Intracellular cytokine staining was used to measure antigen-specific production of IFN-y, TNF-a and IL-2, by CD4+ (FIGS. 7A, 7C) or CD8+ T cells (FIGS. 7B, 7D). Log2 foldchange over PBS group and two-way ANOVA for each profile against the naive group and corrected for Dunnett’s multiple comparisons test are depicted (*p < 0.05; **p < 0.01; ***p < 0.001; ****p < 0.0001).

[0067] FIGS. 8A-8P show in vivo cross-protection of direct challenge and passive transfer / challenge of mHA vaccines at a low dose in mice. FIGS. 8A-8B depict the vaccination regimen and experimental workflow. BALB / c mice (n = 10) were vaccinated in a two-dose vaccination of 1 or 0.1 pg of HA of the different vaccines in a 3-4 week interval after high priming with 105PFU of mH8 / BYam virus. WIV or split mHA vaccines were tested without adjuvant or with the addition of CpG 1018® (10 pg), CpG 1018® (10 pg) + Alum (50 pg) or AddaVax™ (1 : 1 v:v). A QIV (Flulaval Quadrivalent) vaccinated group and an unvaccinated group (PBS) were included as controls. mH8 / BYam virus prime infection was given intranasally in a total volume of 30 pL 6 months prior the two-dose immunization. (FIG. 8C) Four weeks after second dose mice were challenged with 50mLD50 dose and viral titers were measured from harvested lung homogenate tissues 3 days post infection. Binding of serum antibody titers against B / Lee / 40 HA: IgG (D) IgG2a / IgGl ratio (FIG. 8E), IgGl (FIG. 8F) and IgG2a (FIG. 8G) serum antibody titers against B / Lee / 40 HA recombinant protein was reported as previously described in FIGS. 3A-3O. Passive transfer challenge (FIGS. 8H-8P) with 5 mLD50 of B / Lee / 40 virus was performed as previously described in FIGS. 3A-3O. Weight loss (FIGS. 8H, 8K, 8N), survival (FIGS. 81, 8L, 80), and minimumweight (FIGS. 8 J, 8M, 8P) were reported. Kruskal -Wallis test corrected using Dunn’s test for multiple comparisons are depicted (*P < 0.05; **P < 0.01; ***p < 0.001; ****P<0.0001).5. DETAILED DESCRIPTION5.1 Immunogenic Compositions

[0068] In one aspect, provided herein are immunogenic compositions comprising a mosaic hemagglutinin (HA) and a CpG oligonucleotide adjuvant described herein. In some embodiments, provided herein are immunogenic compositions comprising a mosaic HA and a CpG oligonucleotide adjuvant described herein in an admixture with a pharmaceutically acceptable carrier. In some embodiments, provided herein are immunogenic compositions comprising an inactivated influenza virus (e.g., influenza B virus) and a CpG oligonucleotide adjuvant described herein, wherein the inactivated influenza virus comprises a mosaic HA described herein. In some embodiments, provided herein are immunogenic compositions comprising an inactivated influenza virus (e.g., influenza B virus) and a CpG oligonucleotide adjuvant described herein in an admixture with a pharmaceutically acceptable carrier, wherein the inactivated influenza virus comprises a mosaic HA described herein. In some embodiments, provided herein are immunogenic compositions comprising an inactivated split influenza B virus and a CpG oligonucleotide adjuvant described herein in an admixture with a pharmaceutically acceptable carrier, wherein the inactivated split influenza B virus comprises a mosaic HA described herein. In specific embodiments, the mosaic HA is one described in this Section or Section 5.3 or 6, infra. In specific embodiments, the mosaic HA comprises the amino acid sequence of a mosaic HA set forth in Table 3. In some embodiments, the mosaic HA comprises the ectodomain of a mosaic HA set forth in Table 3. In specific embodiments, the CpG oligonucleotide adjuvant is one described in this Section or Section 5.2 or 6, infra. In some embodiments, the immunogenic composition comprises an aluminum salt (e.g., aluminum hydroxide, amorphous aluminum hydroxyphosphate sulfate, aluminum hydroxide, aluminum phosphate, or potassium aluminum sulfate, or a combination thereof). In some embodiments, the immunogenic composition does not comprise an aluminum salt (e.g., aluminum hydroxide, amorphous aluminum hydroxyphosphate sulfate, aluminum hydroxide, aluminum phosphate, or potassium aluminum sulfate, or a combination thereof).

[0069] In some embodiments, provided herein is an immunogenic composition comprising a mosaic HA described herein and a CpG oligonucleotide adjuvant, wherein theCpG oligonucleotide adjuvant comprises an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84). In some embodiments, provided herein is an immunogenic composition comprising a mosaic HA described herein and a CpG oligonucleotide adjuvant in an admixture with a pharmaceutically acceptable carrier, wherein the CpG oligonucleotide adjuvant comprises an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84). In specific embodiments, the mosaic HA is one described in this Section or Section 5.3 or 6, infra. In specific embodiments, the mosaic HA comprises the ectodomain of a mosaic HA set forth in Table 3. In specific embodiments, the CpG oligonucleotide adjuvant is one described in this Section or Section 5.2 or 6, infra. In some embodiments, the immunogenic composition described herein comprises an aluminum salt (e.g, aluminum hydroxide, amorphous aluminum hydroxyphosphate sulfate, aluminum hydroxide, aluminum phosphate, or potassium aluminum sulfate, or a combination thereof). In some embodiments, the immunogenic composition described herein does not comprise an aluminum salt (e.g, aluminum hydroxide, amorphous aluminum hydroxyphosphate sulfate, aluminum hydroxide, aluminum phosphate, or potassium aluminum sulfate, or a combination thereof).

[0070] In some embodiments, provided herein is an immunogenic composition comprising an inactivated influenza virus (e.g., influenza B virus) and a CpG oligonucleotide adjuvant, wherein the inactivated influenza virus comprises a mosaic HA described herein, and wherein the CpG oligonucleotide adjuvant comprises an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84). In some embodiments, provided herein is an immunogenic composition comprising an inactivated influenza virus (e.g., influenza B virus) and a CpG oligonucleotide adjuvant in an admixture with a pharmaceutically acceptable carrier, wherein the inactivated influenza virus comprises a mosaic HA described herein, and wherein the CpG oligonucleotide adjuvant comprises an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84). In some embodiments, provided herein is an immunogenic composition comprising an inactivated split influenza B virus and a CpG oligonucleotide adjuvant, wherein the inactivated split influenza B virus comprises a mosaic HA described herein, and wherein the CpG oligonucleotide adjuvant comprises an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84). In some embodiments, provided herein is an immunogenic composition comprising an inactivated split influenza Bvirus and a CpG oligonucleotide adjuvant in an admixture with a pharmaceutically acceptable carrier, wherein the inactivated split influenza B virus comprises a mosaic HA described herein, and wherein the CpG oligonucleotide adjuvant comprises an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84). In specific embodiments, the mosaic HA is one described in this Section or Section 5.3 or 6, infra. In specific embodiments, the mosaic HA comprises the amino acid sequence of a mosaic HA set forth in Table 3. In some embodiments, the mosaic HA comprises the ectodomain of a mosaic HA set forth in Table 3. In specific embodiments, the CpG oligonucleotide adjuvant is one described in this Section or Section 5.2 or 6, infra. In some embodiments, the immunogenic composition described herein does not comprise an aluminum salt (e.g, aluminum hydroxide, amorphous aluminum hydroxyphosphate sulfate, aluminum hydroxide, aluminum phosphate, or potassium aluminum sulfate, or a combination thereof). In some embodiments, the immunogenic composition described herein comprises an aluminum salt (e.g, aluminum hydroxide, amorphous aluminum hydroxyphosphate sulfate, aluminum hydroxide, aluminum phosphate, or potassium aluminum sulfate, or a combination thereof).

[0071] In another aspect, provided herein are immunogenic compositions comprising a mosaic HA described herein, a CpG oligonucleotide adjuvant described herein, and an aluminum salt. In some embodiments, provided herein are immunogenic compositions comprising a mosaic HA described herein, a CpG oligonucleotide adjuvant described herein, and an aluminum salt in an admixture with a pharmaceutically acceptable carrier. In some embodiments, provided herein are immunogenic compositions comprising an inactivated influenza virus (e.g., influenza B virus), a CpG oligonucleotide adjuvant described herein, and an aluminum salt, wherein the inactivated influenza virus comprises a mosaic HA described herein. In some embodiments, provided herein are immunogenic compositions comprising an inactivated influenza virus (e.g., influenza B virus), a CpG oligonucleotide adjuvant described herein, and an aluminum salt in an admixture with a pharmaceutically acceptable carrier, wherein the inactivated influenza virus comprises a mosaic HA described herein. In some embodiments, provided herein are immunogenic compositions comprising an inactivated split influenza virus (e.g., influenza B virus), a CpG oligonucleotide adjuvant described herein, and an aluminum salt, wherein the inactivated split influenza virus comprises a mosaic HA described herein. In some embodiments, provided herein are immunogenic compositions comprising an inactivated split influenza virus (e.g., influenza B virus), a CpG oligonucleotide adjuvant described herein, and an aluminum salt in anadmixture with a pharmaceutically acceptable carrier, wherein the inactivated split influenza virus comprises a mosaic HA described herein. In specific embodiments, the mosaic HA is one described in this Section or Section 5.3 or 6, infra. In specific embodiments, the mosaic HA comprises the amino acid sequence of a mosaic HA set forth in Table 3. In some embodiments, the mosaic HA comprises the ectodomain of a mosaic HA set forth in Table 3. In some embodiments, the CpG oligonucleotide adjuvant is one described in this Section or Section 5.2 or 6, infra. In some embodiment, the aluminum salt is one described in this Section or Section 6, infra.

[0072] In some embodiments, provided herein is an immunogenic composition comprising an inactivated influenza virus (e.g., influenza B virus), a CpG oligonucleotide adjuvant, and an aluminum salt, wherein the inactivated influenza virus comprises a mosaic HA described herein, and wherein the CpG oligonucleotide adjuvant comprises an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84). In some embodiments, provided herein is an immunogenic composition comprising an inactivated influenza virus (e.g., influenza B virus), a CpG oligonucleotide adjuvant, and an aluminum salt in an admixture with a pharmaceutically acceptable carrier, wherein the inactivated influenza virus comprises a mosaic HA described herein, and wherein the CpG oligonucleotide adjuvant comprises an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84). In some embodiments, provided herein is an immunogenic composition comprising an inactivated split influenza B virus, a CpG oligonucleotide adjuvant, and an aluminum salt, wherein the inactivated split influenza B virus comprises a mosaic HA described herein, and wherein the CpG oligonucleotide adjuvant comprises an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84). In some embodiments, provided herein is an immunogenic composition comprising an inactivated split influenza B virus, a CpG oligonucleotide adjuvant, and an aluminum salt in an admixture with a pharmaceutically acceptable carrier, wherein the inactivated split influenza B virus comprises a mosaic HA described herein, and wherein the CpG oligonucleotide adjuvant comprises an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84). In specific embodiments, the mosaic HA is one described in this Section or Section 5.3 or 6, infra. In specific embodiments, the mosaic HA comprises the amino acid sequence of a mosaic HA set forth in Table 3. In some embodiments, the mosaic HA comprises the ectodomain of a mosaic HA set forth in Table 3.In some embodiments, the CpG oligonucleotide adjuvant is one described in this Section or Section 5.2 or 6, infra. In some embodiment, the aluminum salt is one described in this Section or Section 6, infra.

[0073] In some embodiments, an immunogenic composition described herein comprises from about 3.75 pg to about 150 pg of HA (e.g., a mosaic HA). In some embodiments, an immunogenic composition described herein comprises from about 3.75 pg to about 75 pg of HA (e.g., a mosaic HA). In some embodiments, an immunogenic composition described herein comprises from about 3.75 pg to about 50 pg of HA (e.g., a mosaic HA). In some embodiments, an immunogenic composition described herein comprises from about 3.75 pg to about 25 pg of HA (e.g, a mosaic HA). In some embodiments, an immunogenic composition described herein comprises from about 3.75 pg to about 15 pg of HA (e.g, a mosaic HA). In some embodiments, an immunogenic composition described herein comprises from about 3.75 pg to about 10 pg of HA (e.g., a mosaic HA). In some embodiments, an immunogenic composition described herein comprises from about 10 pg to about 150 pg of HA (e.g., a mosaic HA). In some embodiments, an immunogenic composition described herein comprises from about 10 pg to about 75 pg of HA (e.g., a mosaic HA). In some embodiments, an immunogenic composition described herein comprises from about 50 pg to about 150 pg of HA (e.g., a mosaic HA). In some embodiments, an immunogenic composition described herein comprises from about 50 pg to about 100 pg of HA (e.g., a mosaic HA). In some embodiments, an immunogenic composition described herein comprises from about 50 pg to about 150 pg of HA (e.g., a mosaic HA). In some embodiments, an immunogenic composition described herein comprises from about 75 pg to about 150 pg of HA (e.g., a mosaic HA). In some embodiments, an immunogenic composition described herein comprises from about 25 pg to about 100 pg of HA (e.g., a mosaic HA). In some embodiments, an immunogenic composition described herein comprises from about 25 pg to about 75 pg of HA (e.g., a mosaic HA). In some embodiments, an immunogenic composition described herein comprises from about 10 pg to about 50 pg of HA (e.g., a mosaic HA). In some embodiments, an immunogenic composition described herein comprises from about 10 pg to about 25 pg of HA (e.g., a mosaic HA). In some embodiments, an immunogenic composition described herein comprises from about 0.1 pg to about 5 pg of HA (e.g., a mosaic HA). In some embodiments, an immunogenic composition described herein comprises from about 10 pg to about 15 pg of HA (e.g., a mosaic HA). In some embodiments, an immunogenic composition described herein comprises from about 10 pg toabout 60 pg of HA (e.g., a mosaic HA). In some embodiments, an immunogenic composition described herein comprises from about 5 pg to about 50 pg of HA (e.g., a mosaic HA). In some embodiments, an immunogenic composition described herein comprises from about 5 pg to about 45 pg of HA (e.g., a mosaic HA). In some embodiments, an immunogenic composition described herein comprises from about 5 pg to about 40 pg of HA (e.g., a mosaic HA). In some embodiments, an immunogenic composition described herein comprises from about 10 pg to about 40 pg of HA (e.g., a mosaic HA). In some embodiments, an immunogenic composition described herein comprises from about 10 pg to about 35 pg of HA (e.g., a mosaic HA). In some embodiments, an immunogenic composition described herein comprises from about 15 pg to about 35 pg of HA (e.g., a mosaic HA). In some embodiments, an immunogenic composition described herein comprises from about 15 pg to about 30 pg of HA (e.g., a mosaic HA). In some embodiments, an immunogenic composition described herein comprises about 3.75 pg of HA (e.g., a mosaic HA). In some embodiments, an immunogenic composition described herein comprises about 5 pg of HA (e.g., a mosaic HA). In some embodiments, an immunogenic composition described herein comprises about 10 pg of HA (e.g., a mosaic HA). In some embodiments, an immunogenic composition described herein comprises about 15 pg of HA (e.g., a mosaic HA). In some embodiments, an immunogenic composition described herein comprises about 20 pg of HA (e.g., a mosaic HA). In some embodiments, an immunogenic composition described herein comprises about 25 pg of HA (e.g., a mosaic HA). In some embodiments, an immunogenic composition described herein comprises about 30 pg of HA (e.g., a mosaic HA).

[0074] In some embodiments, the mosaic HA comprises an amino acid sequence that is at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to the amino acid sequence of SEQ ID NO: 38. In some embodiments, the mosaic HA comprises an amino acid sequence that is at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to the amino acid sequence of SEQ ID NO: 40. In some embodiments, the mosaic HA comprises an amino acid sequence that is at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to the amino acid sequence of SEQ ID NO: 42. In some embodiments, the mosaic HA comprises an amino acid sequence that is at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to the amino acid sequence of SEQ ID NO: 44. In some embodiments, the mosaic HA comprises an amino acid sequence that is at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to the amino acidsequence of SEQ ID NO: 46. In some embodiments, the mosaic HA comprises an amino acid sequence that is at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to the amino acid sequence of SEQ ID NO: 48.

[0075] In specific embodiments, the mosaic HA comprises the amino acid sequence of SEQ ID NO: 38. In specific embodiments, the mosaic HA comprises the amino acid sequence of SEQ ID NO: 40. In specific embodiments, the mosaic HA comprises the amino acid sequence of SEQ ID NO: 42. In specific embodiments, the mosaic HA comprises the amino acid sequence of SEQ ID NO: 44. In specific embodiments, the mosaic HA comprises the amino acid sequence of SEQ ID NO: 46. In specific embodiments, the mosaic HA comprises the amino acid sequence of SEQ ID NO: 48.

[0076] In some embodiments, the mosaic HA comprises the ectodomain of the amino acid sequence of SEQ ID NO: 38. In specific embodiments, the mosaic HA comprises the ectodomain of the amino acid sequence of SEQ ID NO: 40. In specific embodiments, the mosaic HA comprises the ectodomain of the amino acid sequence of SEQ ID NO: 42. In specific embodiments, the mosaic HA comprises the ectodomain of the amino acid sequence of SEQ ID NO: 44. In specific embodiments, the mosaic HA comprises the ectodomain of the amino acid sequence of SEQ ID NO: 46. In specific embodiments, the mosaic HA comprises the ectodomain of the amino acid sequence of SEQ ID NO: 48.

[0077] In some embodiments, an immunogenic composition described herein comprises from about 1 pg to about 50 pg of a CpG oligonucleotide adjuvant. In some embodiments, an immunogenic composition described herein comprises from about 5 pg to about 50 pg of a CpG oligonucleotide adjuvant. In some embodiments, an immunogenic composition described herein comprises from about 5 pg to about 40 pg of a CpG oligonucleotide adjuvant. In some embodiments, an immunogenic composition described herein comprises from about 5 pg to about 30 pg of a CpG oligonucleotide adjuvant. In some embodiments, an immunogenic composition described herein comprises from about 5 pg to about 25 pg of a CpG oligonucleotide adjuvant. In some embodiments, an immunogenic composition described herein comprises from about 5 pg to about 20 pg of a CpG oligonucleotide adjuvant. In some embodiments, an immunogenic composition described herein comprises from about 5 pg to about 10 pg of a CpG oligonucleotide adjuvant. In some embodiments, an immunogenic composition described herein comprises about 1 pg, about 2 pg, about 3 pg, about 4 pg, or about 5 pg of a CpG oligonucleotide adjuvant. In some embodiments, an immunogenic composition described herein comprises about 6 pg, about 7 pg, about 8 pg, about 9 pg, or about 10 pg of a CpG oligonucleotide adjuvant. In some embodiments, animmunogenic composition described herein comprises about 11 pg, about 12 pg, about 13 pg, about 14 pg, or about 15 pg of a CpG oligonucleotide adjuvant. In some embodiments, an immunogenic composition described herein comprises about 20 pg, about 25 pg, about 30 pg, about 40 pg, or about 50 pg of a CpG oligonucleotide adjuvant.

[0078] In some embodiments, an immunogenic composition described herein comprises from about 375 pg to about 6000 pg of a CpG oligonucleotide of a CpG oligonucleotide adjuvant described herein (e.g., in Section 5.2 or Example 1), preferably from about 500 pg to about 5000 pg of the CpG oligonucleotide, preferably from about 750 pg to about 3000 pg of the CpG oligonucleotide. In some embodiments, an immunogenic composition described herein comprises greater than about 250 pg, about 500 pg, about 750 pg, about 1000 pg, or about 1250 pg of the CpG oligonucleotide of a CpG oligonucleotide adjuvant described herein (e.g., in Section 5.2 or Example 1), and less than about 6000 pg, about 5000 pg, about 4000 pg, about 3000 pg, or about 2000 pg of the CpG oligonucleotide. In some embodiments, an immunogenic composition described herein comprises about 375 pg, about 750 pg, about 1500 pg, about 3000 pg or about 6000 pg of the CpG oligonucleotide of a CpG oligonucleotide adjuvant. In some embodiments, an immunogenic composition comprises about 750 pg of the CpG oligonucleotide adjuvant described herein (e.g., in Section 5.2 or Example 1). In some embodiments, an immunogenic composition described herein comprises about 1500 pg of the CpG oligonucleotide of a CpG oligonucleotide adjuvant described herein (e.g., in Section 5.2 or Example 1). In some embodiments, an immunogenic composition described herein comprises about 3000 pg of the CpG oligonucleotide of a CpG oligonucleotide adjuvant described herein (e.g., in Section 5.2 or Example 1). In some embodiments, an immunogenic composition described herein comprises about 6000 pg of the CpG oligonucleotide of a CpG oligonucleotide adjuvant described herein (e.g., in Section 5.2 or Example 1).

[0079] In some embodiments, the oligonucleotide of the CpG oligonucleotide adjuvant comprises the nucleotide sequence of 5’-TGACTGTGAACGTTCGAGATGA-3’ (SEQ ID NO: 85). In some embodiments, the oligonucleotide of the CpG oligonucleotide adjuvant is 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, or 35 nucleotides in length. In some embodiments, the oligonucleotide of the CpG oligonucleotide adjuvant is a single stranded oligodeoxynucleotide. In some embodiments, the oligonucleotide of the CpG oligonucleotide adjuvant comprises only phosphorothioate linkages, or a combination of one or more phosphodiester linkages and one or more phosphorothioate linkages. In someembodiments, the oligonucleotide of the CpG oligonucleotide adjuvant is fully RNA or is an RNA / DNA chimera.

[0080] In some embodiments, an immunogenic composition described herein comprises from about 5 pg to about 50 pg of an aluminum salt. In some embodiments, an immunogenic composition described herein comprises from about 5 pg to about 25 pg of an aluminum salt. In some embodiments, an immunogenic composition described herein comprises from about 5 pg to about 15 pg of an aluminum salt. In some embodiments, an immunogenic composition described herein comprises from about 15 pg to about 25 pg of an aluminum salt. In some embodiments, an immunogenic composition described herein comprises from about 15 pg to about 50 pg of an aluminum salt. In some embodiments, an immunogenic composition described herein comprises about 5 pg, about 15 pg, about 25 pg, or about 50 pg of an aluminum salt.

[0081] In some embodiments, an immunogenic composition described herein comprises from about 0.25 to about 1.25 mg of Ah+. In some embodiments, an immunogenic composition comprises from about 0.50 to about 1.00 mg of an Ah+. In some embodiments, the immunogenic composition comprises about 0.375 mg, about 0.75 mg, or about 1.00 mg of Ah+. In some embodiments, the immunogenic composition comprises about 0.375 mg of A13+.

[0082] In some embodiments, an immunogenic composition described herein comprises about 0.05% to about 3%, or about 1% to about 3% of aluminum salt. In some embodiments, an immunogenic composition described herein comprises about 1%, about 1.5%, about 2%, about 2.5%, or about 3% of aluminum salt. In some embodiments, an immunogenic composition described herein comprises about 1% or about 2% of an aluminum salt.

[0083] In some embodiments, the aluminum salt comprises one or more selected from the group consisting of amorphous aluminum hydroxyphosphate sulfate, aluminum hydroxide, aluminum phosphate, potassium aluminum sulfate, and a combination thereof. In some embodiments, the aluminum salt comprises one or both of aluminum hydroxide and aluminum phosphate. In some embodiments, the aluminum salt comprises aluminum hydroxide. In some embodiments, the aluminum salt comprises aluminum phosphate. In some embodiments, an immunogenic composition described herein does not comprise an aluminum salt.

[0084] In specific embodiments, an aluminum salt functions as an adjuvant.

[0085] In some embodiments, provided herein are immunogenic compositions comprising a mosaic HA described herein. In some embodiments, provided herein areimmunogenic compositions comprising a mosaic HA described herein in an admixture with a pharmaceutically acceptable carrier. In some embodiments, the immunogenic composition comprises an aluminum salt described herein. The immunogenic compositions may be used in combination with a CpG oligonucleotide adjuvant described herein to immunize a subject (e.g., a human subject) against influenza virus disease (e.g., influenza virus disease caused by influenza B virus) and / or to prevent influenza virus disease (e.g., influenza virus disease caused by influenza B virus).

[0086] In some embodiments, an immunogenic composition described herein further comprises a group 1 chimeric HA, such as, e.g., described in Nachbagauer et al., 2016, npj Vaccines 131 1, 1-10, and / or Nachbagauer et al., 2021, Nature Medicine 27, 106-114. In some embodiments, the group 1 chimeric HA comprises the globular head domain of an influenza A virus (e.g., H5, H8, Hl 1, Hl 3 or Hl 5) heterologous to the stem domain of a group 1 influenza A virus HA (e.g., an influenza A virus Hl). In some embodiments, the globular head domain is from an exotic influenza A virus HA (e.g., an exotic avian influenza A virus HA). In some embodiments, an immunogenic composition described herein further comprises a group 1 chimeric HA, wherein the group 1 chimeric HA comprises the HA globular head domain of an influenza virus H8 and the HA stem domain of an influenza virus Hl. In some embodiments, an immunogenic composition described herein further comprises a group 1 chimeric HA, wherein the group 1 chimeric HA comprises the HA globular head domain of an influenza virus H8 and the HA stem domain of an influenza A virus A / California / 04 / 09 HA. In some embodiments, an immunogenic composition described herein further comprises a group 1 chimeric HA, wherein the group 1 chimeric HA comprises the HA globular head domain of an influenza A virus A / mallard / Sweden / 24 / 02 HA and the HA stem domain of an influenza A virus A / Califomia / 04 / 09 HA. In some embodiments, an immunogenic composition described herein further comprises a group 1 chimeric HA, wherein the group 1 chimeric HA comprises the HA globular head domain of an influenza virus H5 and the HA stem domain of an influenza A virus Hl. In some embodiments, an immunogenic composition described herein further comprises a group 1 chimeric HA, wherein the group 1 chimeric HA comprises the HA globular head domain of an influenza virus H5 and the HA stem domain of an influenza A virus A / California / 04 / 09 HA. In some embodiments, an immunogenic composition described herein further comprises a group 1 chimeric HA, wherein the group 1 chimeric HA comprises the HA globular head domain of an influenza A virus A / Vietnam / 1203 / 04 HA and the HA stem domain of an influenza A virus A / California / 04 / 09 HA.

[0087] In some embodiments, an immunogenic composition described herein further comprises a group 2 chimeric HA, such as, e.g., described in Puente-Mas saguer et al., 2023, Sci. Adv. 9(37): eadi4753. In some embodiments, the group 2 chimeric HA comprises the globular head domain of an influenza A virus (e.g., H5, H8, Hl 1, H13 or H15) heterologous to the stem domain of a group 2 influenza A virus HA (e.g., an influenza A virus H3). In some embodiments, the globular head domain is from an exotic influenza A virus HA (e.g., an exotic avian influenza A virus HA). In some embodiments, an immunogenic composition described herein further comprises a group 2 chimeric HA, wherein the group 2 chimeric HA comprises the HA globular head domain of an influenza A virus H4, H5, H7, H8, Hl 1, or Hl 5 and the HA stem domain of an influenza A virus H3. In some embodiments, an immunogenic composition described herein further comprises a group 2 chimeric HA, wherein the group 2 chimeric HA comprises the HA globular head domain of an influenza virus H4, H5, H7, H8, Hl 1, or Hl 5 and the HA stem domain of an influenza A virus A / Hong Kong / 4801 / 2014, A / Perth / 16 / 2009, or A / duck / Ukraine / 63. In some embodiments, the HA globular head domain is the HA globular head domain of A / duck / Czechoslovakia / 1956 (H3N2) or A / wedge-tailed shearwater / Western Australia / 2576 / 1979 (H15N9).

[0088] In some embodiments, an immunogenic composition described herein does not further comprises a group 1 chimeric HA. In some embodiments, an immunogenic composition described herein does not further comprises a group 2 chimeric HA. In some embodiments, an immunogenic composition described herein does not further comprises a group 1 chimeric HA and a group 2 chimeric HA.

[0089] In some embodiments, an immunogenic composition described herein has a volume of about 0.5 mL to about 2 mL. In some embodiments, an immunogenic composition described herein has a volume of about 0.5 mL, about 1 mL, about 1.5 mL, or about 2 mL.

[0090] As used herein, the term “pharmaceutically acceptable” means approved by a regulatory agency of the Federal or a state government or listed in the U.S. Pharmacopeia or other generally recognized pharmacopoeia for use in animals, and more particularly in humans. The term “carrier” refers to a diluent, adjuvant, excipient, or vehicle with which the pharmaceutical composition is administered. In specific embodiments, the pharmaceutically acceptable carrier is a diluent, excipient, or vehicle. For example, the pharmaceutically acceptable carrier is a diluent e.g., saline). Saline solutions and aqueous dextrose and glycerol solutions can also be employed as liquid carriers, particularly for injectable solutions. Suitable excipients include starch, glucose, lactose, sucrose, gelatin, malt, rice, flour, chalk, silica gel, sodium stearate, glycerol monostearate, talc, sodium chloride, driedskim milk, glycerol, propylene, glycol, water, ethanol and the like. Examples of suitable pharmaceutical carriers are described in “Remington’s Pharmaceutical Sciences” by E.W. Martin. The formulation should suit the mode of administration.

[0091] In specific embodiments, an immunogenic composition described herein is formulated to be suitable for the intended route of administration to a subject. For example, an immunogenic composition may be formulated to be suitable for parenteral, oral, intradermal, intranasal, transdermal, or intraperitoneal administration. In a specific embodiment, an immunogenic composition may be formulated for intravenous, oral, intraperitoneal, intranasal, intratracheal, subcutaneous, intramuscular, topical, intradermal, transdermal, or pulmonary administration. In a specific embodiment, an immunogenic composition may be formulated for intramuscular administration. In another specific embodiment, an immunogenic composition may be formulated for subcutaneous administration. In another specific embodiment, an immunogenic composition may be formulated for intranasal administration. In another specific embodiment, an immunogenic composition may be formulated for pulmonary administration.

[0092] In specific embodiments, provided herein is an immunogenic composition described in Section 6, infra.

[0093] An immunogenic composition described herein may be used to induce an immune response to one, two, or multiple (e.g., 3, 4, 5, 6, or more) influenza viruses (e.g., influenza B viruses) in a subject (e.g., human subject). In specific embodiments, an immunogenic composition described herein may be used to induce a cross-reactive immune response to two or more (e.g., 3, 4, 5, 6, or more) influenza viruses (e.g., influenza B viruses) in a subject (e.g., human subject). An immunogenic composition described herein may be used to induce an immune response that provides protection (e.g., full or partial protection) against one, two, or multiple (e.g., 3, 4, 5, 6, or more) influenza viruses (e.g., an influenza B virus) in a subject (e.g., human subject). In some embodiments, the immune response induced provides protection (e.g., full or partial protection) against a homologous influenza B virus. In some embodiments, the immune response induced provides protection (e.g., full or partial protection) against a heterotypic influenza B virus. An immunogenic composition described herein may be used to immunize a subject (e.g., human subject) against influenza virus (e.g., influenza B virus). An immunogenic composition described herein may also be used to prevent an influenza virus disease (e.g., influenza virus disease caused by influenza B virus in a subject (e.g., human subject). An immunogenic composition described herein may also be used to reduce the severity of an influenza virus disease (e.g., influenza virus disease causedby influenza B virus in a subject (e.g., human subject). In a specific embodiment, an immunogenic composition described herein may be used in a method described herein.

[0094] In some embodiments, provided herein is the use of an immunogenic composition described herein the manufacture of a medicament for inducing an immune response (e.g., an immune response that is capable of cross-reacting with a plurality of influenza B virus strains and lineages) in a subject (e.g., human subject). In some embodiments, provided herein is the use of an immunogenic composition described herein the manufacture of a medicament for immunizing a subject (e.g., a human) against influenza virus disease (e.g., influenza virus disease caused by an influenza B virus). In some embodiments, provided herein is the use of an immunogenic composition described herein the manufacture of a medicament for preventing influenza virus disease (e.g., influenza virus disease caused by an influenza B virus) a subject (e.g., a human).

[0095] In specific embodiments, an immunogenic composition described herein is a vaccine.

[0096] The immunogenic compositions described herein can be included in a container, pack, or dispenser together with instructions for administration.

[0097] In a specific embodiment, provided herein is a composition (e.g., a pharmaceutical composition) comprising an antibody(ies) that binds to influenza virus HA (e.g., an influenza B virus HA), which was generated using an immunogenic composition described herein. The composition may further comprise a pharmaceutically acceptable carrier. The antibody may be polyclonal or monoclonal. In some embodiments, the antibody is human or humanized. The antibody(ies) may be used to passively immunize a subject (e.g., a human subject) against influenza virus disease (e.g., influenza B virus disease).5.2 CpG Oligonucleotide Adjuvants

[0098] Toll-like receptors are expressed in and on dendritic cells and other innate immune cells and are among the most important receptors for stimulating a response to the presence of invading pathogens. Humans have multiple types of TLRs that are similar in structure but recognize different parts of viruses or bacteria. By activating specific TLRs, it is possible to stimulate and control specific types of innate immune responses that can be harnessed to enhance adaptive responses.

[0099] TLR9 (CD289) recognizes unmethylated cytidine-phospho-guanosine (CpG) motifs found in microbial DNA, which can be mimicked using synthetic CpG-containing oligodeoxynucleotides (CpG-ODNs). CpG-ODNs are known to enhance antibody production and to stimulate T helper 1 (Thl) cell responses (Coffman et al., Immunity, 33:492-503, 2010). Based on structure and biological function, CpG-ODNs have been divided into three general classes: CpG-A, CpG-B, and CpG-C (Campbell, Methods Mol Biol, 1494: 15-27, 2017). The degree of B cell activation varies between the classes with CpG-A ODNs being weak, CpG-C ODNs being good, and CpG-B ODNs being strong B cell activators.

[0100] In specific embodiments, a mosaic HA described herein or inactivated influenza virus or inactivated split virus described herein is administered in an immunogenic composition comprising a CpG oligonucleotide adjuvant, or a mosaic HA described herein or inactivated influenza virus or inactivated split virus described herein is administered in combination with a CpG oligonucleotide adjuvant. In specific embodiments, the compositions described herein comprise, or are administered in combination with, a CpG oligonucleotide adjuvant. The CpG oligonucleotide adjuvants of the present disclosure are TLR9 agonists. In specific embodiments, CpG oligonucleotide adjuvants of the present disclosure are good B cell activators (CpG-C ODN) or more preferably strong (CpG-B ODN) B cell activators.

[0101] Optimal oligonucleotide TLR9 agonists often contain a palindromic sequence following the general formula of: 5’-purine-purine-CG-pyrimidine-pyrimidine-3’, or 5’- purine-purine-CG-pyrimidine-pyrimidine-CG-3’ (U.S. Patent No. 6,589,940). TLR9 agonism is also observed with certain non-palindromic CpG-enriched phosphorothioate oligonucleotides, but may be affected by changes in the nucleotide sequence. Additionally, TLR9 agonism is abolished by methylation of the cytosine within the CpG dinucleotide. Accordingly in some embodiments, a CpG oligonucleotide adjuvant comprises an oligonucleotide of from 8 to 35 nucleotides in length comprising the sequence 5’-AACGTTCG-3’ (SEQ ID NO: 82). In some embodiments, the oligonucleotide is greater than 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 nucleotides in length, and the oligonucleotide is less than 35, 34, 33, 32, 31, 30, 29, 28, 27, 26, 25, or 24 nucleotides in length. In some embodiments, a CpG oligonucleotide adjuvant comprises an oligonucleotide of from 10 to 35 nucleotides in length comprising the sequence 5’-AACGTTCGAG-3’ (SEQ ID NO: 83). In some embodiments, the oligonucleotide is greater than 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 nucleotides in length, and the oligonucleotide is less than 35, 34, 33, 32, 31, 30, 29, 28, 27, 26, 25, or 24 nucleotides in length. In some embodiments, a CpG oligonucleotide adjuvant comprises an oligonucleotide of from 10 to 35 nucleotides in length comprising the sequence 5’-GAACGTTCG-3’ (SEQ ID NO: 84). In some embodiments, the oligonucleotide is greater than 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 nucleotides in length, and the oligonucleotide is less than 35, 34, 33, 32, 31, 30, 29, 28, 27, 26, 25, or 24 nucleotides in length.

[0102] Researchers at Dynavax Technologies Corporation (Emeryville, CA) have identified a 22-mer phosphorothioate linked oligodeoxynucleotide, CpG 1018® adjuvant, which contains specific sequences that can substantially enhance the immune response to coadministered antigens across species (Campbell JD. Development of the CpG Adjuvant 1018: A Case Study. Methods Mol Biol. 2017;1494: 15-27. doi: 10.1007 / 978-l-4939-6445-l_2. PMID: 27718183). CpG 1018® adjuvant has a nucleotide sequence of 5’- TGACTGTGAACGTTCGAGATGA-3’ (SEQ ID NO: 85) and was chosen after screening a broad panel of oligonucleotides for immunostimulatory activity in vitro and in vivo. CpG 1018® adjuvant is a CpG-B ODN that is active in mice, rabbits, dogs, baboons, cynomolgus monkeys, and humans. CpG 1018® adjuvant is also referred to by the term ODN 1018. In specific embodiments, a CpG oligonucleotide adjuvant (e.g., as described herein Section 5.2 or Example 1) comprises an oligonucleotide comprising the sequence of SEQ ID NO: 85. In some embodiments, a CpG oligonucleotide adjuvant comprises an oligonucleotide of from 22 to 35 nucleotides in length comprising the sequence of SEQ ID NO: 85. In some embodiments, the oligonucleotide is greater than 22, 23, 24, 25, 26, 27, 28, 29, 30 or 31 nucleotides in length, and the oligonucleotide is less than 35, 34, 33, 32, 31, 30, 29, 28, 27, 26, 25, or 24 nucleotides in length.

[0103] Although the exemplary CpG oligonucleotide adjuvant, CpG 1018® adjuvant, is a CpG-ODN, the present disclosure is not restricted to fully DNA molecules. That is, in some embodiments, the oligonucleotide of the CpG oligonucleotide adjuvant is a DNA / RNA chimeric molecule in which the CpG(s) and the palindromic sequence are deoxyribonucleicacids and one or more nucleic acids outside of these regions are ribonucleic acids. In some embodiments, the oligonucleotide of the CpG oligonucleotide adjuvant is linear. In other embodiments, the oligonucleotide of the CpG oligonucleotide adjuvant is circular or includes hairpin loop(s). The oligonucleotide of the CpG oligonucleotide adjuvant may be single stranded. Alternatively, the oligonucleotide of the CpG oligonucleotide adjuvant may be double stranded.

[0104] In some embodiments, the CpG oligonucleotide of the CpG oligonucleotide adjuvant may contain modifications. Modifications include but are not limited to, modifications of the 3 ’OH or 5 ’OH group, modifications of the nucleotide base, modifications of the sugar component, and modifications of the phosphate group. Modified bases may be included in the palindromic sequence of the CpG oligonucleotide as long as the modified base(s) maintains the same specificity for its natural complement through Watson- Crick base pairing (e.g., the palindromic portion is still self-complementary). In some embodiments, the CpG oligonucleotide comprises a non-canonical base. In some embodiments, the CpG oligonucleotide comprises a modified nucleoside. In some embodiments, the modified nucleoside is selected from the group consisting of 2’-deoxy-7- deazaguanosine, 2’-deoxy-6-thioguanosine, arabinoguanosine, 2’-deoxy-2’substituted- arabinoguanosine, and 2’-O-substituted-arabinoguanosine.

[0105] The CpG oligonucleotide of the CpG oligonucleotide adjuvant may contain a modification of the phosphate group. For example, in addition to phosphodiester linkages, phosphate modifications include, but are not limited to, phosphorothioate (e.g., phosphoromonothioate), phosphorodithioate, methyl phosphonate, phosphoramidate (bridging or non-bridging), and phosphotriester, and may be used in any combination. Other non-phosphate oligomer linkages may also be used. In some embodiments, the oligonucleotides comprise only phosphorothioate backbones. In some embodiments, the oligonucleotides comprise only phosphorodithioate backbones. In some embodiments, the oligonucleotides comprise only phosphodiester backbones. In some embodiments, the oligonucleotide comprises a combination of phosphate linkages in the phosphate backbone such as a combination of phosphodiester and phosphorothioate linkages. In some embodiments, the oligonucleotide comprises a combination of phosphate linkages in the phosphate backbone such as a combination of phosphodiester, phosphorothioate, and phosphorodithioate linkages. Oligonucleotides with thioated phosphate (e.g., phosphorothioate) backbones can be more immunogenic than those with phosphodiester backbones and appear to be more resistant to degradation after injection into the host [18,19], The CpG oligonucleotide of an CpG oligonucleotide adjuvant of the present disclosure include at least one, two or three intemucleotide phosphorothioate ester linkages. In some embodiments, when a plurality of CpG oligonucleotide molecules are present in a pharmaceutical composition comprising at least one excipient, both stereoisomers of the phosphorothioate ester linkage are present in the plurality of CpG oligonucleotide molecules. In some embodiments, all of the internucleotide linkages of the CpG oligonucleotide are phosphorothioate linkages, or said another way, the CpG oligonucleotide has a phosphorothioate backbone.

[0106] In some embodiments, the CpG oligonucleotide of the CpG oligonucleotide adjuvant is produced synthetically, or is an isolated natural product or fragment thereof. In some embodiments, a CpG oligonucleotide is synthesized using H-phosphonate, phosphotriester, phosphodiester, phosphite-triester, and / or phosphoramidite chemistry. In some embodiments, a the CpG oligonucleotide of the CpG oligonucleotide adjuvant is synthesized using a solid support, optionally controlled pore glass. In some embodiments, a CpG oligonucleotide is thioated using environmental sulfur (S8), Beaucage reagent, a thioazoline derivative (i.e., DtsNH, EDITH, MEDITH, ADTT, DDTT), or sulfurizing reagent II (Glen Research). In some embodiments, the CpG oligonucleotide of the CpG oligonucleotide adjuvant is purified using column chromatography (e.g., HPLC).

[0107] The CpG oligonucleotides are in their pharmaceutically acceptable salt form unless otherwise indicated. In specific embodiments, a CpG oligonucleotide adjuvant described herein comprises a pharmaceutically acceptable salt form. Exemplary basic salts include ammonium salts, alkali metal salts such as sodium, lithium, and potassium salts, alkaline earth metal salts such as calcium and magnesium salts, zinc salts, salts with organic bases (for example, organic amines) such as N-Me-D-glucamine, N-[l-(2,3- dioleoyloxy)propyl]-N,N,N-trimethylammonium chloride, choline, tromethamine, dicyclohexylamines, t-butyl amines, and salts with amino acids such as arginine, lysine and the like. In some embodiment, the CpG oligonucleotides are in the ammonium, sodium, lithium, or potassium salt form. In one preferred embodiment, the CpG oligonucleotides are in the sodium salt form. In a specific embodiment, a CpG oligonucleotide adjuvant described herein comprises an aluminum salt. In some embodiments, the aluminum salt comprises one or more selected from the group consisting of amorphous aluminum hydroxyphosphate sulfate, aluminum hydroxide, aluminum phosphate, and potassium aluminum sulfate. The aluminum salt may be aluminum hydroxide or aluminum phosphate. In a specific embodiment, the aluminum salt comprises aluminum hydroxide and aluminum phosphate. Ina specific embodiment, the aluminum salt comprises aluminum phosphate. In a specific embodiment, the aluminum salt is aluminum hydroxide. In some embodiments, the CpG oligonucleotide adjuvant described herein does not comprise an aluminum salt.

[0108] In a specific embodiment, a CpG oligonucleotide adjuvant comprises CpG 1018® adjuvant. In a specific embodiment, a CpG oligonucleotide adjuvant is one described in Section 6, infra.

[0109] In some embodiments, a CpG oligonucleotide adjuvant described herein (e.g., in Example 1) enhances or boosts an immune response to influenza virus (e.g., an influenza B virus) and does not produce an allergy or other adverse reaction. For example, the CpG oligonucleotide adjuvant can enhance an immune response by several mechanisms including, e.g., lymphocyte recruitment, stimulation of B and / or T cells, stimulation of macrophages. In specific embodiments, a CpG oligonucleotide adjuvant described herein enhances or boosts an immune response to a mosaic HA, or an inactivated or inactivated split influenza virus (e.g., influenza B virus) such as described in Example 1, infra.5.3 Mosaic HA

[0110] In one aspect, provided herein are mosaic hemagglutinin (HA) polypeptides comprising an HA ectodomain of an influenza B virus HA in which immunodominant epitopes in one or more (e.g, 1, 2, 3, or 4) major antigenic sites (e.g, the 120 loop, the 150 loop, the 160 loop, and / or 190 helix) in the globular head domain of the HA ectodomain are silenced. Without being bound by any theory, the silencing of the immunodominant epitopes in one or more (e.g., 1, 2, 3, or 4) major antigenic sites in the globular head domain of the HA ectodomain redirects the immune system to the more conserved epitopes in the HA (e.g., conserved epitopes the HA globular head domain and / or HA stalk domain) to achieve a cross-protective immune response. In some embodiments, provided herein are mosaic HAs comprising an influenza B virus HA ectodomain in which immunodominant epitopes in one or more (e.g., 1, 2, 3, or 4) major antigenic sites (e.g., the 120 loop, the 150 loop, the 160 loop, and / or 190 helix) in the globular head domain of the HA ectodomain are replaced with corresponding sequences from influenza A virus HAs (e.g., exotic influenza A virus HAs, such as, e.g., H5, H8, Hl 1, or Hl 3). In specific embodiments, the replacement of the immunodominant epitopes in one or more major antigenic sites with corresponding sequences from influenza A virus HAs does not affect the conformation / structure of the HA. In some embodiments, provided herein are mosaic HAs comprising an HA ectodomain of an influenza B virus HA comprising 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 or more amino acidchanges (e.g., substitutions, deletions and / or additions) in immunodominant epitopes of one or more (e.g., 1, 2, 3, or 4) major antigenic sites of the globular head domain of the HA ectodomain (e.g., 120 loop, 150 loop, 160 loop and / or 190 helix), wherein the amino acid changes (e.g., substitutions) replace 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 or more amino acid residues in the epitopes of one or more major antigenic sites of the globular head domain of the HA ectodomain with random amino acid residues that do not affect the conformation / structure of the HA. In some embodiments, provided herein are mosaic HAs comprising an HA ectodomain of an influenza B virus HA comprising 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 or more amino acid changes (e.g., substitutions) within two, three, or four major antigenic sites of the globular head domain of the HA ectodomain (e.g., 120 loop, 150 loop, 160 loop and / or 190 helix), wherein the amino acid changes (e.g., substitutions) replace 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 or more amino acid residues in the loop of the globular head domain of the HA ectodomain with random amino acid residues that do not affect the conformation / structure of the HA. In some embodiments, provided herein are mosaic HAs comprising an HA ectodomain of an influenza B virus HA in which one or more (e.g., 1, 2, 3, 4 or more) irrelevant epitopes are introduced into one or more (e.g., 1, 2, 3, or 4) major antigenic sites of the globular head domain of the HA ectodomain (e.g., 120 loop, 150 loop, 160 loop and / or 190 helix). In some embodiments, the one or more irrelevant epitopes consist of glycines and / or alanines. In specific embodiments, the introduction of the one or more irrelevant epitopes does not affect the conformation / structure of the HA. In some embodiments, the mosaic HAs further comprise the transmembrane and cytoplasmic domains of the influenza B virus HA. In some embodiments, the mosaic HAs further comprise a trimerization domain (e.g., T4 fibritin (foldon) trimerization domain or GCN4-based isoleucine zipper trimerization domain).

[0111] In some embodiments, provided herein are mosaic HAs comprising an HA ectodomain of an influenza B virus comprising 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 or more amino acid changes (e.g., substitutions, deletions, and / or additions) within an antigenic site of the globular head domain of the influenza B virus HA, wherein the amino acid changes change (e.g., substitute) 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 or more amino acid residues in the loop of the globular head of the HA ectodomain to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA. In some embodiments, provided herein are mosaic HA polypeptides comprising an HA ectodomain of an influenza B virus comprising 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 or more amino acid changes (e.g., substitutions, deletions, and / or additions) in the 120 loop, 150 loop, 160 loop, and / or190 helix of the globular head domain of the HA ectodomain, wherein the amino acid changes change (e.g., substitute) 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 or more amino acid residues in the 120 loop, 150 loop, 160 loop, and / or 190 helix of the globular head of the influenza B virus HA to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA. In some embodiments, the HA ectodomain of the influenza B virus HA comprises 1, 2, 3, 4, or more compensatory mutations (e.g., compensatory amino acid substitutions). In some embodiments, the influenza B virus HA is the HA of an influenza B virus disclosed herein (e.g., influenza B virus B / Yamagata / 16 / 1988 HA, B / Brisbane / 60 / 2008 HA, or B / Phuket / 3073 / 2013 HA), n some embodiments, the influenza B virus HA is the HA of an influenza B virus disclosed herein in FIG. 1G or 1H. In some embodiments, the influenza A virus HA is the HA of an influenza A virus disclosed herein (e.g., A / Vietnam / 1203 / 04 (H5N1) HA; A / mallard / Sweden / 24 / 02 (H8N4) HA; A / shoveler / Netherlands / 18 / 99 (Hl 1N9) HA; or A / black-headed gull / Sweden / 1 / 99 (H13N6) HA). In some embodiments, the mosaic HA further comprises the transmembrane domain or cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises the transmembrane domain and cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises a trimerization domain (e.g., T4 fibritin (foldon) trimerization domain or GCN4-based isoleucine zipper trimerization domain).

[0112] In some embodiments, provided herein are mosaic HA polypeptides comprising an HA ectodomain of an influenza B virus HA with 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,15, 16, 17, 18, 19, 20 or more amino acid changes (e.g., substitutions, deletions, and / or additions) within the 120 loop of the globular head domain of the HA ectodomain, wherein the amino acid changes change (e.g., substitute) 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,16, 17, 18, 19, 20 or more amino acid residues in the 120 loop of the globular head of the HA ectodomain to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA. In some embodiments, the HA ectodomain of the influenza B virus HA comprises 1, 2, 3, 4, or more compensatory mutations (e.g., compensatory amino acid substitutions). In some embodiments, the mosaic HA further comprises the transmembrane domain or cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises the transmembrane domain and cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises a trimerization domain (e.g., T4 fibritin (foldon) trimerization domain or GCN4-based isoleucine zipper trimerization domain). In some embodiments, the influenza Bvirus HA is the HA of an influenza B virus disclosed herein (e.g., influenza B virus B / Yamagata / 16 / 1988 HA, B / Brisbane / 60 / 2008 HA, or B / Phuket / 3073 / 2013 HA). In some embodiments, the influenza B virus HA is the HA of an influenza B virus disclosed in FIG. 1G or 1H. In some embodiments, the influenza A virus HA is the HA of an influenza A virus disclosed herein (e.g., A / Vietnam / 1203 / 04 (H5N1) HA; A / mallard / Sweden / 24 / 02 (H8N4) HA; A / shoveler / Netherlands / 18 / 99 (Hl 1N9) HA; or A / black-headed gull / Sweden / 1 / 99 (H13N6) HA). In some embodiments, the HA ectodomain is from influenza B virus B / Yamagata / 16 / 1988 HA and the 120 loop comprises the amino acid sequence TIP and the amino acid sequence of SEQ ID NO: 1 (see also Table 2). In some embodiments, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more amino acid residues in the amino acid sequence TIP and the amino acid sequence of SEQ ID NO: 1 in the 120 loop of the HA ectodomain of the influenza B virus B / Yamagata / 16 / 1988 HA are changed (e.g., substituted) to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA (e.g., A / Vietnam / 1203 / 04 (H5N1) HA; A / mallard / Sweden / 24 / 02 (H8N4) HA; A / shoveler / Netherlands / 18 / 99 (H11N9) HA; or A / black-headed gull / Sweden / 1 / 99 (H13N6) HA). In some embodiments, the amino acid sequence TIP and the amino acid sequence of SEQ ID NO: 1 in the 120 loop of the HA ectodomain of the influenza B virus B / Yamagata / 16 / 1988 HA are changed to: (i) the amino acid sequence FIP and the amino acid sequence of SEQ ID NO: 5, respectively; (ii) the amino acid sequence HIP and the amino acid sequence of SEQ ID NO: 9, respectively; (iii) the amino acid sequence LIP and the amino acid sequence of SEQ ID NO: 13, respectively; or (iv) the amino acid sequence NIP and the amino acid sequence of SEQ ID NO: 17, respectively. In some embodiments, the HA ectodomain is from influenza B virus B / Brisbane / 60 / 2008 HA and the 120 loop comprises the amino acid sequence KIP and the amino acid sequence of SEQ ID NO: 21 (see also Table 2). In some embodiments, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more amino acid residues in the amino acid sequence KIP and the amino acid sequence of SEQ ID NO: 21 in the 120 loop of the HA ectodomain of the influenza B virus B / Brisbane / 60 / 2008 HA are changed (e.g., substituted) to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA (e.g., A / Vietnam / 1203 / 04 (H5N1) HA;A / mallard / Sweden / 24 / 02 (H8N4) HA; A / shoveler / Netherlands / 18 / 99 (H11N9) HA; or A / black-headed gull / Sweden / 1 / 99 (H13N6) HA). In some embodiments, the amino acid sequence KIP and the amino acid sequence of SEQ ID NO: 21 in the 120 loop of the HA ectodomain of the influenza B virus B / Brisbane / 60 / 2008 HA are changed to the amino acidsequence NIP and the amino acid sequence of SEQ ID NO: 25, respectively. In some embodiments, the HA ectodomain is from influenza B virus B / Phuket / 3073 / 2013 HA and the 120 loop comprises the amino acid sequence TTP and the amino acid sequence of SEQ ID NO: 29 (see also Table 2). In some embodiments, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more amino acid residues in the amino acid sequence TTP and the amino acid sequence of SEQ ID NO: 29 in the 120 loop of the HA ectodomain of the influenza B virus B / Phuket / 3073 / 2013 HA are changed (e.g., substituted) to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA (e.g., A / Vietnam / 1203 / 04 (H5N1) HA; A / mallard / Sweden / 24 / 02 (H8N4) HA; A / shoveler / Netherlands / 18 / 99 (Hl 1N9) HA; or A / black-headed gull / Sweden / 1 / 99 (H13N6) HA). In some embodiments, the amino acid sequence TTP and the amino acid sequence of SEQ ID NO: 29 in the 120 loop of the HA ectodomain of the influenza B virus B / Phuket / 3073 / 2013 HA are changed to the amino acid sequence FTP and the amino acid sequence of SEQ ID NO: 33, respectively. In some embodiments, the 120 loop of the mosaic HA comprises the consensus sequence for the 120 loop in Table 2.

[0113] In some embodiments, provided herein are mosaic HA polypeptides comprising an HA ectodomain of an influenza B virus HA with 1, 2, 3, 4, 5, 6, 7, 8, or more amino acid changes (e.g., substitutions, deletions, and / or additions) within the 150 loop of the globular head domain of the HA ectodomain, wherein the amino acid changes change (e.g., substitute) 1, 2, 3, 4, 5, 6, 7, 8, or more amino acid residues in the 150 loop of the globular head of the influenza B virus HA to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA. In some embodiments, the HA ectodomain of the influenza B virus HA comprises 1, 2, 3, 4, or more compensatory mutations (e.g., compensatory amino acid substitutions). In some embodiments, the mosaic HA further comprises the transmembrane domain or cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises the transmembrane domain and cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises a trimerization domain (e.g., T4 fibritin (foldon) trimerization domain or GCN4-based isoleucine zipper trimerization domain). In some embodiments, the influenza B virus HA is the HA of an influenza B virus disclosed herein (e.g., influenza B virus B / Yamagata / 16 / 1988 HA, B / Brisbane / 60 / 2008 HA, or B / Phuket / 3073 / 2013 HA). In some embodiments, the influenza B virus HA is the HA of an influenza B virus disclosed in FIG. 1G or 1H. In some embodiments, the influenza A virus HA is the HA of an influenza A virus disclosed herein (e.g., A / Vietnam / 1203 / 04 (H5N1) HA; A / mallard / Sweden / 24 / 02(H8N4) HA; A / shoveler / Netherlands / 18 / 99 (Hl 1N9) HA; or A / black-headed gull / Sweden / 1 / 99 (H13N6) HA). In some embodiments, the HA ectodomain is from influenza B virus B / Yamagata / 16 / 1988 HA and the 150 loop comprises the amino acid sequence of SEQ ID NO: 2 (see also Table 2). In some embodiments, 1, 2, 3, 4, 5, 6, 7, 8, or more amino acid residues in the amino acid sequence of SEQ ID NO: 2 in the 150 loop of the HA ectodomain of the influenza B virus B / Yamagata / 16 / 1988 HA are changed (e.g., substituted) to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA (e.g., A / Vietnam / 1203 / 04 (H5N1) HA;A / mallard / Sweden / 24 / 02 (H8N4) HA; A / shoveler / Netherlands / 18 / 99 (H11N9) HA; or A / black-headed gull / Sweden / 1 / 99 (H13N6) HA). In some embodiments, the amino acid sequence of SEQ ID NO: 2 in the 150 loop of the HA ectodomain of the influenza B virus B / Yamagata / 16 / 1988 HA are changed to: (i) the amino acid sequence of SEQ ID NO: 7; (ii) the amino acid sequence of SEQ ID NO: 11; (iii) the amino acid sequence of SEQ ID NO: 15; or (iv) the amino acid sequence of SEQ ID NO: 19. In some embodiments, the HA ectodomain is from influenza B virus B / Brisbane / 60 / 2008 HA and the 150 loop comprises the amino acid sequence of SEQ ID NO: 22 (see also Table 2). In some embodiments, 1, 2, 3, 4, 5, 6, 7, 8, or more amino acid residues in the amino acid sequence of SEQ ID NO: 22 in the 150 loop of the HA ectodomain of the influenza B virus B / Brisbane / 60 / 2008 HA are changed (e.g., substituted) to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA (e.g., A / Vietnam / 1203 / 04 (H5N1) HA; A / mallard / Sweden / 24 / 02 (H8N4) HA; A / shoveler / Netherlands / 18 / 99 (H11N9) HA; or A / black-headed gull / Sweden / 1 / 99 (H13N6) HA). In some embodiments, the amino acid sequence of SEQ ID NO: 22 in the 150 loop of the HA ectodomain of the influenza B virus B / Brisbane / 60 / 2008 HA is changed to the amino acid sequence of SEQ ID NO: 26. In some embodiments, the HA ectodomain is from influenza B virus B / Phuket / 3073 / 2013 HA and the 150 loop comprises the amino acid sequence of SEQ ID NO: 30 (see also Table 2). In some embodiments, 1, 2, 3, 4, 5, 6, 7, 8, or more amino acid residues in the amino acid sequence of SEQ ID NO: 30 in the 150 loop of the HA ectodomain of the influenza B virusB / Phuket / 3073 / 2013 HA are changed (e.g., substituted) to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA (e.g., A / Vietnam / 1203 / 04 (H5N1) HA; A / mallard / Sweden / 24 / 02 (H8N4) HA;A / shoveler / Netherlands / 18 / 99 (Hl 1N9) HA; or A / black-headed gull / Sweden / 1 / 99 (H13N6) HA). In some embodiments, the amino acid sequence of SEQ ID NO: 30 in the 150 loop of the HA ectodomain of the influenza B virus B / Phuket / 3073 / 2013 HA is changed to the aminoacid sequence of SEQ ID NO: 34. In some embodiments, the 150 loop of the mosaic HA comprises the consensus sequence for the 150 loop in Table 2.

[0114] In some embodiments, provided herein are mosaic HA polypeptides comprising an HA ectodomain of an influenza B virus with 1, 2, 3, 4, 5 or more amino acid changes (e.g., substitutions, deletions, and / or additions) within 160 loop of the globular head domain of the HA ectodomain, wherein the amino acid changes (e.g., substitutions) change 1, 2, 3, 4, 5 or more amino acid residues in the 160 loop of the globular head of the HA ectodomain with amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA. In some embodiments, the HA ectodomain of the influenza B virus HA comprises 1, 2, 3, 4, or more compensatory mutations (e.g., compensatory amino acid substitutions). In some embodiments, the mosaic HA further comprises the transmembrane domain or cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises the transmembrane domain and cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises a trimerization domain (e.g, T4 fibritin (foldon) trimerization domain or GCN4-based isoleucine zipper trimerization domain). In some embodiments, the influenza B virus HA is the HA of an influenza B virus disclosed herein (e.g, influenza B virus B / Yamagata / 16 / 1988 HA, B / Brisbane / 60 / 2008 HA, or B / Phuket / 3073 / 2013 HA). In some embodiments, the influenza B virus HA is the HA of an influenza B virus disclosed in FIG. 1G or 1H. In some embodiments, the influenza A virus HA is the HA of an influenza A virus disclosed herein (e.g., A / Vietnam / 1203 / 04 (H5N1) HA; A / mallard / Sweden / 24 / 02 (H8N4) HA;A / shoveler / Netherlands / 18 / 99 (Hl 1N9) HA; or A / black-headed gull / Sweden / 1 / 99 (H13N6) HA). In some embodiments, the HA ectodomain is from influenza B virus B / Yamagata / 16 / 1988 HA and the 160 loop comprises the amino acid sequence of SEQ ID NO: 3 (see also Table 2). In some embodiments, 1, 2, 3, 4, 5 or more amino acid residues in the amino acid sequence of SEQ ID NO: 3 in the 160 loop of the HA ectodomain of the influenza B virus B / Yamagata / 16 / 1988 HA are changed (e.g., substituted) to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA (e.g., A / Vietnam / 1203 / 04 (H5N1) HA; A / mallard / Sweden / 24 / 02 (H8N4) HA;A / shoveler / Netherlands / 18 / 99 (Hl 1N9) HA; or A / black-headed gull / Sweden / 1 / 99 (H13N6) HA). In some embodiments, the amino acid sequence of SEQ ID NO: 3 in the 160 loop of the HA ectodomain of the influenza B virus B / Yamagata / 16 / 1988 HA is changed to: (i) the amino acid sequence of SEQ ID NO: 7; (ii) the amino acid sequence of SEQ ID NO: 11; (iii) the amino acid sequence of SEQ ID NO: 15; or (iv) the amino acid sequence of SEQ ID NO:19. In some embodiments, the HA ectodomain is from influenza B virus B / Brisbane / 60 / 2008 HA and the 160 loop comprises the amino acid sequence of SEQ ID NO: 23 (see also Table 2). In some embodiments, 1, 2, 3, 4, 5 or more amino acid residues in the amino acid sequence of SEQ ID NO: 23 in the 160 loop of the HA ectodomain of the influenza B virus B / Brisbane / 60 / 2008 HA are changed (e.g., substituted) to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA (e.g., A / Vietnam / 1203 / 04 (H5N1) HA; A / mallard / Sweden / 24 / 02 (H8N4) HA;A / shoveler / Netherlands / 18 / 99 (Hl 1N9) HA; or A / black-headed gull / Sweden / 1 / 99 (H13N6) HA). In some embodiments, the amino acid sequence of SEQ ID NO: 23 in the 160 loop of the HA ectodomain of the influenza B virus B / Brisbane / 60 / 2008 HA is changed to the amino acid sequence of SEQ ID NO: 27. In some embodiments, the HA ectodomain is from influenza B virus B / Phuket / 3073 / 2013 HA and the 160 loop comprises the amino acid sequence of SEQ ID NO: 31 (see also Table 2). In some embodiments, 1, 2, 3, 4, 5 or more amino acid residues in the amino acid sequence of SEQ ID NO: 31 in the 160 loop of the HA ectodomain of the influenza B virus B / Phuket / 3073 / 2013 HA are changed (e.g., substituted) to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA (e.g., A / Vietnam / 1203 / 04 (H5N1) HA; A / mallard / Sweden / 24 / 02 (H8N4) HA; A / shoveler / Netherlands / 18 / 99 (Hl 1N9) HA; or A / black-headed gull / Sweden / 1 / 99 (H13N6) HA). In some embodiments, the amino acid sequence of SEQ ID NO: 31 in the 160 loop of the HA ectodomain of the influenza B virus B / Phuket / 3073 / 2013 HA is changed to the amino acid sequence of SEQ ID NO: 35. In some embodiments, the 160 loop of the mosaic HA comprises the consensus sequence for the 160 loop in Table 2.

[0115] In some embodiments, provided herein are mosaic HA polypeptides comprising an HA ectodomain of an influenza B virus HA with 2, 3, 4, 5, 6, 7, 8 or more amino acid changes (e.g., substitutions, deletions and / or additions) within the 190 helix of the globular head domain of the HA ectodomain, wherein the amino acid changes change (e.g., substitute) 1, 2, 3, 4, 5, 6, 7, 8 or more amino acid residues in the 190 helix of the globular head of the HA ectodomain to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA. In some embodiments, the HA ectodomain of the influenza B virus HA comprises 1, 2, 3, 4, or more compensatory mutations (e.g., compensatory amino acid substitutions). In some embodiments, the mosaic HA further comprises the transmembrane domain or cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises the transmembrane domain and cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HAfurther comprises a trimerization domain (e.g., T4 fibritin (foldon) trimerization domain or GCN4-based isoleucine zipper trimerization domain). In some embodiments, the influenza B virus HA is the HA of an influenza B virus disclosed herein (e.g., influenza B virus B / Yamagata / 16 / 1988 HA, B / Brisbane / 60 / 2008 HA, or B / Phuket / 3073 / 2013 HA). In some embodiments, the influenza B virus HA is the HA of an influenza B virus disclosed in FIG. 1G or 1H. In some embodiments, the influenza A virus HA is the HA of an influenza A virus disclosed herein (e.g., A / Vietnam / 1203 / 04 (H5N1) HA; A / mallard / Sweden / 24 / 02 (H8N4) HA; A / shoveler / Netherlands / 18 / 99 (Hl 1N9) HA; or A / black-headed gull / Sweden / 1 / 99 (H13N6) HA). In some embodiments, the HA ectodomain is from influenza B virus B / Yamagata / 16 / 1988 HA and the 190 helix comprises the amino acid sequence of SEQ ID NO: 4 (see also Table 2). In some embodiments, 1, 2, 3, 4, 5, 6, 7, 8, or more amino acid residues in the amino acid sequence of SEQ ID NO: 4 in the 190 helix of the HA ectodomain of the influenza B virus B / Yamagata / 16 / 1988 HA are changed (e.g., substituted) to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA (e.g., A / Vietnam / 1203 / 04 (H5N1) HA;A / mallard / Sweden / 24 / 02 (H8N4) HA; A / shoveler / Netherlands / 18 / 99 (H11N9) HA; or A / black-headed gull / Sweden / 1 / 99 (H13N6) HA). In some embodiments, the amino acid sequence of SEQ ID NO: 4 in the 190 helix of the HA ectodomain of the influenza B virus B / Yamagata / 16 / 1988 HA is changed to: (i) the amino acid sequence of SEQ ID NO: 8; (ii) the amino acid sequence of SEQ ID NO: 12; (iii) the amino acid sequence of SEQ ID NO: 16; or (iv) the amino acid sequence of SEQ ID NO: 20. In some embodiments, the HA ectodomain is from influenza B virus B / Brisbane / 60 / 2008 HA and the 190 helix comprises the amino acid sequence of SEQ ID NO: 24 (see also Table 2). In some embodiments, 1, 2, 3, 4, 5, 6, 7, 8, or more amino acid residues in the amino acid sequence of SEQ ID NO: 24 in the 190 helix of the HA ectodomain of the influenza B virus B / Brisbane / 60 / 2008 HA are changed (e.g., substituted) to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA (e.g., A / Vietnam / 1203 / 04 (H5N1) HA; A / mallard / Sweden / 24 / 02 (H8N4) HA; A / shoveler / Netherlands / 18 / 99 (H11N9) HA; or A / black-headed gull / Sweden / 1 / 99 (H13N6) HA). In some embodiments, the amino acid sequence of SEQ ID NO: 24 in the 190 helix of the HA ectodomain of the influenza B virus B / Brisbane / 60 / 2008 HA is changed to the amino acid sequence of SEQ ID NO: 28 or 37. In some embodiments, the HA ectodomain is from influenza B virus B / Phuket / 3073 / 2013 HA and the 190 helix comprises the amino acid sequence of SEQ ID NO: 32 (see also Table 2). In some embodiments, 1, 2, 3, 4, 5, 6, 7, 8, or more amino acid residues in the amino acidsequence of SEQ ID NO: 32 in the 190 helix of the HA ectodomain of the influenza B virus B / Phuket / 3073 / 2013 HA are changed (e.g., substituted) to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA (e.g., A / Vietnam / 1203 / 04 (H5N1) HA; A / mallard / Sweden / 24 / 02 (H8N4) HA;A / shoveler / Netherlands / 18 / 99 (Hl 1N9) HA; or A / black-headed gull / Sweden / 1 / 99 (H13N6) HA). In some embodiments, the amino acid sequence of SEQ ID NO: 32 in the 190 helix of the HA ectodomain of the influenza B virus B / Phuket / 3073 / 2013 HA is changed to the amino acid sequence of SEQ ID NO: 36. In some embodiments, the 190 helix of the mosaic HA comprises the consensus sequence for the 190 helix in Table 2.

[0116] In some embodiments, provided herein are mosaic HAs comprising an HA ectodomain of influenza B virus HA, wherein the HA ectodomain comprises (A) an HA stalk domain of the influenza B virus and (B) an HA globular head domain of the influenza B virus with amino acid changes (e.g., substitutions, deletions, and / or additions) in one, two, three or all of the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain and 0,I, 2, or 3 compensatory mutations (e.g., compensatory amino acid substitutions) outside of the 120 loop, 150 loop, the 160 loop, and 190 helix, wherein: (i) the amino acid changes (e.g., substitutions, deletions, and / or additions) in the 120 loop comprise 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,I I, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more amino acid changes (e.g., substitutions, deletions, and / or additions), wherein the amino acid changes (e.g., substitutions, deletions, and / or additions) change 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more amino acid residues in the 120 loop of the HA globular head of the influenza B virus HA to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA; (ii) the amino acid changes (e.g., substitutions, deletions, and / or additions) in the 150 loop comprise 1, 2, 3, 4, 5, 6, 7, 8, or more amino acid changes (e.g., substitutions, deletions, and / or additions), wherein the amino acid changes (e.g., substitutions, deletions, and / or additions) change 1, 2, 3, 4, 5, 6, 7, 8, or more amino acid residues in the 150 loop of the globular head of the influenza B virus HA to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA; (iii) the amino acid changes (e.g., substitutions, deletions, and / or additions) in the 160 loop comprise 1, 2, 3, 4, 5 or more amino acid changes (e.g., substitutions, deletions, and / or additions), wherein the amino acid changes (e.g., substitutions, deletions, and / or additions) change 1, 2, 3, 4, 5 or more amino acid residues in the 160 loop of the globular head of the influenza B virus HA to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA; and (iv) the amino acid changes (e.g., substitutions,deletions, and / or additions) in the 190 helix comprise 1, 2, 3, 4, 5, 6, 7, 8 or more amino acid changes (e.g., substitutions, deletions, and / or additions), wherein the amino acid changes (e.g., substitutions, deletions, and / or additions) change 1, 2, 3, 4, 5, 6, 7, 8 or more amino acid residues in the 190 helix of the globular head of the influenza B virus HA to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA. In some embodiments, the amino acid residues changed in one, two, three, or all of the 120 loop, 150 loop, 160 loop, and 190 helix are changed to amino acid residues found in a corresponding region of the same influenza A virus HA. In some embodiments, the influenza B virus HA is the HA of an influenza B virus disclosed herein (e.g., influenza B virus B / Yamagata / 16 / 1988 HA, B / Brisbane / 60 / 2008 HA, or B / Phuket / 3073 / 2013 HA). In some embodiments, the influenza B virus HA is the HA of an influenza B virus disclosed in FIG. 1G or 1H. In some embodiments, the influenza A virus HA is the HA of an influenza A virus disclosed herein (e.g., A / Vietnam / 1203 / 04 (H5N1) HA; A / mallard / Sweden / 24 / 02 (H8N4) HA; A / shoveler / Netherlands / 18 / 99 (Hl 1N9) HA; or A / black-headed gull / Sweden / 1 / 99 (H13N6) HA). In some embodiments, the mosaic HA further comprises the transmembrane domain or cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises the transmembrane domain and cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises a trimerization domain (e.g., T4 fibritin (foldon) trimerization domain or GCN4- based isoleucine zipper trimerization domain).

[0117] In some embodiments, provided herein are mosaic HAs comprising an HA ectodomain of an influenza B virus HA, wherein the HA ectodomain comprises (A) an HA stalk domain of the influenza B virus and (B) an HA globular head domain of the influenza B virus with amino acid changes (e.g., substitutions, deletions, and / or additions) in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain and 0, 1, 2, or 3 compensatory mutations (e.g., compensatory amino acid substitutions) outside of the 120 loop, 150 loop, the 160 loop, and 190 helix, wherein: (i) the amino acid changes (e.g., substitutions, deletions, and / or additions) in the 120 loop comprise 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more amino acid changes (e.g., substitutions, deletions, and / or additions), wherein the amino acid changes (e.g., substitutions, deletions, and / or additions) change 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more amino acid residues in the 120 loop of the HA globular head of the influenza B virus HA to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA; (ii) the amino acid changes (e.g., substitutions, deletions, and / oradditions) in the 150 loop comprise 1, 2, 3, 4, 5, 6, 7, 8, or more amino acid changes (e.g., substitutions, deletions, and / or additions), wherein the amino acid changes (e.g., substitutions, deletions, and / or additions) change 1, 2, 3, 4, 5, 6, 7, 8, or more amino acid residues in the 150 loop of the globular head of the influenza B virus HA to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA; (iii) the amino acid changes e.g., substitutions, deletions, and / or additions) in the 160 loop comprise 1, 2, 3, 4, 5 or more amino acid changes e.g., substitutions, deletions, and / or additions), wherein the amino acid changes e.g., substitutions, deletions, and / or additions) change 1, 2, 3, 4, 5 or more amino acid residues in the 160 loop of the globular head of the influenza B virus HA to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA; and (iv) the amino acid changes (e.g., substitutions, deletions, and / or additions) in the 190 helix comprise 1, 2, 3, 4, 5, 6, 7, 8 or more amino acid changes e.g., substitutions, deletions, and / or additions), wherein the amino acid changes e.g., substitutions, deletions, and / or additions) change 1, 2, 3, 4, 5, 6, 7, 8 or more amino acid residues in the 190 helix of the globular head of the influenza B virus HA to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA. In some embodiments, the amino acid residues changed in the 120 loop, 150 loop, 160 loop, and 190 helix are changed to amino acid residues found in a corresponding region of the same influenza A virus HA. In some embodiments, the influenza B virus HA is the HA of an influenza B virus disclosed herein (e.g., influenza B virus B / Yamagata / 16 / 1988 HA, B / Brisbane / 60 / 2008 HA, or B / Phuket / 3073 / 2013 HA). In some embodiments, the influenza B virus HA is the HA of an influenza B virus disclosed in FIG. 1G or 1H. In some embodiments, the influenza A virus HA is the HA of an influenza A virus disclosed herein (e.g., A / Vietnam / 1203 / 04 (H5N1) HA; A / mallard / Sweden / 24 / 02 (H8N4) HA;A / shoveler / Netherlands / 18 / 99 (Hl 1N9) HA; or A / black-headed gull / Sweden / 1 / 99 (H13N6) HA). In some embodiments, the mosaic HA further comprises the transmembrane domain or cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises the transmembrane domain and cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises a trimerization domain (e.g., T4 fibritin (foldon) trimerization domain or GCN4-based isoleucine zipper trimerization domain).

[0118] In some embodiments, provided herein are mosaic HAs comprising an HA ectodomain of an influenza B virus HA, wherein the HA ectodomain comprises (A) an HA stalk domain of the influenza B virus and (B) an HA globular head domain of the influenza Bvirus with amino acid substitutions in one, two, three or all of the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain and 0, 1, 2, or 3 compensatory mutations (e.g., compensatory amino acid substitutions) outside of the 120 loop, 150 loop, the 160 loop, and 190 helix, wherein: (i) the amino acid substitutions in the 120 loop comprise 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more amino acid substitutions, wherein the amino acid substitutions substitute 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more amino acid residues in the 120 loop of the HA globular head of the influenza B virus HA to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA; (ii) the amino acid substitutions in the 150 loop comprise 1, 2, 3, 4, 5, 6, 7, 8, or more amino acid substitutions, wherein the amino acid substitutions substitute 1, 2, 3, 4, 5, 6, 7, 8, or more amino acid residues in the 150 loop of the globular head of the influenza B virus HA to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA; (iii) the amino acid substitutions in the 160 loop comprise 1, 2, 3, 4, 5 or more amino acid substitutions, wherein the amino acid substitutions substitute 1, 2, 3, 4, 5 or more amino acid residues in the 160 loop of the globular head of the influenza B virus HA to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA; and (iv) the amino acid substitutions in the 190 helix comprise 1, 2, 3, 4, 5, 6, 7, 8 or more amino acid substitutions, wherein the amino acid substitutions substitute 1, 2, 3, 4, 5, 6, 7, 8 or more amino acid residues in the 190 helix of the globular head of the influenza B virus HA to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA. In some embodiments, the amino acid residues substitutions are in the 120 loop, 150 loop, 160 loop, and 190 helix. In some embodiments, the amino acid residues substitutions in one, two, three, or all of the 120 loop, 150 loop, 160 loop, and 190 helix are substituted to amino acid residues found in a corresponding region of the same influenza A virus HA. In some embodiments, the influenza B virus HA is the HA of an influenza B virus disclosed herein (e.g., influenza B virus B / Yamagata / 16 / 1988 HA, B / Brisbane / 60 / 2008 HA, or B / Phuket / 3073 / 2013 HA). In some embodiments, the influenza B virus HA is the HA of an influenza B virus disclosed in FIG. 1G or 1H. In some embodiments, the influenza A virus HA is the HA of an influenza A virus disclosed herein (e.g., A / Vietnam / 1203 / 04 (H5N1) HA; A / mallard / Sweden / 24 / 02 (H8N4) HA; A / shoveler / Netherlands / 18 / 99 (H11N9) HA; or A / black-headed gull / Sweden / 1 / 99 (H13N6) HA). In some embodiments, the mosaic HA further comprises the transmembrane domain or cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises the transmembranedomain and cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises a trimerization domain (e.g., T4 fibritin (foldon) trimerization domain or GCN4-based isoleucine zipper trimerization domain).

[0119] In some embodiments, the HA ectodomain is from influenza B virus B / Yamagata / 16 / 1988 HA and the 120 loop comprises the amino acid sequence TIP and the amino acid sequence of SEQ ID NO: 1 (see also Table 2). In some embodiments, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more amino acid residues in the amino acid sequence TIP and the amino acid sequence of SEQ ID NO: 1 in the 120 loop of the HA globular head domain of the influenza B virus B / Yamagata / 16 / 1988 HA are changed (e.g., substituted) to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA (e.g., A / Vietnam / 1203 / 04 (H5N1) HA;A / mallard / Sweden / 24 / 02 (H8N4) HA; A / shoveler / Netherlands / 18 / 99 (H11N9) HA; or A / black-headed gull / Sweden / 1 / 99 (H13N6) HA). In some embodiments, the amino acid sequence TIP and the amino acid sequence of SEQ ID NO: 1 in the 120 loop of the HA globular head domain of the influenza B virus B / Yamagata / 16 / 1988 HA are changed to: (i) the amino acid sequence FIP and the amino acid sequence of SEQ ID NO: 5, respectively; (ii) the amino acid sequence HIP and the amino acid sequence of SEQ ID NO: 9, respectively; (iii) the amino acid sequence LIP and the amino acid sequence of SEQ ID NO: 13, respectively; or (iv) the amino acid sequence NIP and the amino acid sequence of SEQ ID NO: 17, respectively. In some embodiments, the HA ectodomain is from influenza B virus B / Brisbane / 60 / 2008 HA and the 120 loop comprises the amino acid sequence KIP and the amino acid sequence of SEQ ID NO: 21 (see also Table 2). In some embodiments, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more amino acid residues in the amino acid sequence KIP and the amino acid sequence of SEQ ID NO: 21 in the 120 loop of the HA globular head domain of the influenza B virus B / Brisbane / 60 / 2008 HA are changed (e.g., substituted) to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA (e.g., A / Vietnam / 1203 / 04 (H5N1) HA;A / mallard / Sweden / 24 / 02 (H8N4) HA; A / shoveler / Netherlands / 18 / 99 (H11N9) HA; or A / black-headed gull / Sweden / 1 / 99 (H13N6) HA). In some embodiments, the amino acid sequence KIP and the amino acid sequence of SEQ ID NO: 21 in the 120 loop of the HA globular head domain of the influenza B virus B / Brisbane / 60 / 2008 HA are changed to the amino acid sequence NIP and the amino acid sequence of SEQ ID NO: 25, respectively. In some embodiments, the HA ectodomain is from influenza B virus B / Phuket / 3073 / 2013 HA and the 120 loop comprises the amino acid sequence TTP and the amino acid sequence ofSEQ ID NO: 29, respectively. In some embodiments, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more amino acid residues in the amino acid sequence TTP and the amino acid sequence of SEQ ID NO: 29 in the 120 loop of the HA globular head domain of the influenza B virus B / Phuket / 3073 / 2013 HA are changed (e.g., substituted) to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA (e.g., A / Vietnam / 1203 / 04 (H5N1) HA; A / mallard / Sweden / 24 / 02 (H8N4) HA; A / shoveler / Netherlands / 18 / 99 (Hl 1N9) HA; or A / black-headed gull / Sweden / 1 / 99 (H13N6) HA). In some embodiments, the amino acid sequence TTP and the amino acid sequence of SEQ ID NO: 29 in the 120 loop of the HA globular head domain of the influenza B virus B / Phuket / 3073 / 2013 HA are changed to the amino acid sequence FTP and the amino acid sequence of SEQ ID NO: 33, respectively. In some embodiments, the 120 loop of the mosaic HA comprises the consensus sequence for the 120 loop in Table 2.

[0120] In some embodiments, the HA ectodomain is from influenza B virus B / Yamagata / 16 / 1988 HA and the 150 loop comprises the amino acid sequence of SEQ ID NO: 2 (see also Table 2). In some embodiments, 1, 2, 3, 4, 5, 6, 7, 8, or more amino acid residues in the amino acid sequence of SEQ ID NO: 2 in the 150 loop of the HA globular head domain of the influenza B virus B / Yamagata / 16 / 1988 HA are changed (e.g., substituted) to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA (e.g., A / Vietnam / 1203 / 04 (H5N1) HA; A / mallard / Sweden / 24 / 02 (H8N4) HA; A / shoveler / Netherlands / 18 / 99 (Hl 1N9) HA; or A / black-headed gull / Sweden / 1 / 99 (H13N6) HA). In some embodiments, the amino acid sequence of SEQ ID NO: 2 in the 150 loop of the HA globular head domain of the influenza B virus B / Yamagata / 16 / 1988 HA are changed to: (i) the amino acid sequence of SEQ ID NO: 7; (ii) the amino acid sequence of SEQ ID NO: 11; (iii) the amino acid sequence of SEQ ID NO: 15; or (iv) the amino acid sequence of SEQ ID NO: 19. In some embodiments, the HA ectodomain is from influenza B virus B / Brisbane / 60 / 2008 HA and the 150 loop comprises the amino acid sequence of SEQ ID NO: 22 (see also Table 2). In some embodiments, 1, 2, 3, 4, 5, 6, 7, 8, or more amino acid residues in the amino acid sequence of SEQ ID NO: 22 in the 150 loop of the HA globular head domain of the influenza B virus B / Brisbane / 60 / 2008 HA are changed (e.g., substituted) to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA (e.g., A / Vietnam / 1203 / 04 (H5N1) HA; A / mallard / Sweden / 24 / 02 (H8N4) HA; A / shoveler / Netherlands / 18 / 99 (H11N9) HA; or A / black-headed gull / Sweden / 1 / 99 (H13N6) HA). In some embodiments, the amino acid sequence of SEQ ID NO: 22 in the 150 loop of the HA globular head domain of the influenzaB virus B / Brisbane / 60 / 2008 HA is changed to the amino acid sequence of SEQ ID NO: 26. In some embodiments, the HA ectodomain is from influenza B virus B / Phuket / 3073 / 2013 HA and the 150 loop comprises the amino acid sequence of SEQ ID NO: 30 (see also Table 2). In some embodiments, 1, 2, 3, 4, 5, 6, 7, 8, or more amino acid residues in the amino acid sequence of SEQ ID NO: 30 in the 150 loop of the HA globular head domain of the influenza B virus B / Phuket / 3073 / 2013 HA are changed (e.g., substituted) to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA (e.g., A / Vietnam / 1203 / 04 (H5N1) HA; A / mallard / Sweden / 24 / 02 (H8N4) HA;A / shoveler / Netherlands / 18 / 99 (Hl 1N9) HA; or A / black-headed gull / Sweden / 1 / 99 (H13N6) HA). In some embodiments, the amino acid sequence of SEQ ID NO: 30 in the 150 loop of the HA globular head domain of the influenza B virus B / Phuket / 3073 / 2013 HA is changed to the amino acid sequence of SEQ ID NO: 34. In some embodiments, the 150 loop of the mosaic HA comprises the consensus sequence for the 150 loop in Table 2.

[0121] In some embodiments, the HA ectodomain is from influenza B virus B / Yamagata / 16 / 1988 HA and the 160 loop comprises the amino acid sequence of SEQ ID NO: 3 (see also Table 2). In some embodiments, 1, 2, 3, 4, 5 or more amino acid residues in the amino acid sequence of SEQ ID NO: 3 in the 160 loop of the HA globular head domain of the influenza B virus B / Yamagata / 16 / 1988 HA are changed (e.g., substituted) to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA (e.g., A / Vietnam / 1203 / 04 (H5N1) HA; A / mallard / Sweden / 24 / 02 (H8N4) HA; A / shoveler / Netherlands / 18 / 99 (Hl 1N9) HA; or A / black-headed gull / Sweden / 1 / 99 (H13N6) HA). In some embodiments, the amino acid sequence of SEQ ID NO: 3 in the 160 loop of the HA globular head domain of the influenza B virus B / Yamagata / 16 / 1988 HA is changed to: (i) the amino acid sequence of SEQ ID NO: 7; (ii) the amino acid sequence of SEQ ID NO: 11; (iii) the amino acid sequence of SEQ ID NO: 15; or (iv) the amino acid sequence of SEQ ID NO: 19. In some embodiments, the HA ectodomain is from influenza B virus B / Brisbane / 60 / 2008 HA and the 160 loop comprises the amino acid sequence of SEQ ID NO: 23 (see also Table 2). In some embodiments, 1, 2, 3, 4, 5 or more amino acid residues in the amino acid sequence of SEQ ID NO: 23 in the 160 loop of the HA globular head domain of the influenza B virus B / Brisbane / 60 / 2008 HA are changed (e.g., substituted) to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA (e.g., A / Vietnam / 1203 / 04 (H5N1) HA; A / mallard / Sweden / 24 / 02 (H8N4) HA;A / shoveler / Netherlands / 18 / 99 (Hl 1N9) HA; or A / black-headed gull / Sweden / 1 / 99 (H13N6) HA). In some embodiments, the amino acid sequence of SEQ ID NO: 23 in the 160 loop ofthe HA globular head domain of the influenza B virus B / Brisbane / 60 / 2008 HA is changed to the amino acid sequence of SEQ ID NO: 27. In some embodiments, the HA ectodomain is from influenza B virus B / Phuket / 3073 / 2013 HA and the 160 loop comprises the amino acid sequence of SEQ ID NO: 31 (see also Table 2). In some embodiments, 1, 2, 3, 4, 5 or more amino acid residues in the amino acid sequence of SEQ ID NO: 31 in the 160 loop of the HA globular head domain of the influenza B virus B / Phuket / 3073 / 2013 HA are changed (e.g., substituted) to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA (e.g., A / Vietnam / 1203 / 04 (H5N1) HA;A / mallard / Sweden / 24 / 02 (H8N4) HA; A / shoveler / Netherlands / 18 / 99 (H11N9) HA; or A / black-headed gull / Sweden / 1 / 99 (H13N6) HA). In some embodiments, the amino acid sequence of SEQ ID NO: 31 in the 160 loop of the HA globular head domain of the influenza B virus B / Phuket / 3073 / 2013 HA is changed to the amino acid sequence of SEQ ID NO: 35. In some embodiments, the 160 loop of the mosaic HA comprises the consensus sequence for the 160 loop in Table 2.

[0122] In some embodiments, the HA ectodomain is from influenza B virus B / Yamagata / 16 / 1988 HA and the 190 helix comprises the amino acid sequence of SEQ ID NO: 4 (see also Table 2). In some embodiments, 1, 2, 3, 4, 5, 6, 7, 8, or more amino acid residues in the amino acid sequence of SEQ ID NO: 4 in the 190 helix of the HA globular head domain of the influenza B virus B / Yamagata / 16 / 1988 HA are changed (e.g., substituted) to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA (e.g., A / Vietnam / 1203 / 04 (H5N1) HA; A / mallard / Sweden / 24 / 02 (H8N4) HA; A / shoveler / Netherlands / 18 / 99 (Hl 1N9) HA; or A / black-headed gull / Sweden / 1 / 99 (H13N6) HA). In some embodiments, the amino acid sequence of SEQ ID NO: 4 in the 190 helix of the HA globular head domain of the influenza B virus B / Yamagata / 16 / 1988 HA is changed to: (i) the amino acid sequence of SEQ ID NO: 8; (ii) the amino acid sequence of SEQ ID NO: 12; (iii) the amino acid sequence of SEQ ID NO: 16; or (iv) the amino acid sequence of SEQ ID NO: 20. In some embodiments, the HA ectodomain is from influenza B virus B / Brisbane / 60 / 2008 HA and the 190 helix comprises the amino acid sequence of SEQ ID NO: 24 (see also Table 2). In some embodiments, 1, 2, 3, 4, 5, 6, 7, 8, or more amino acid residues in the amino acid sequence of SEQ ID NO: 32 in the 190 helix of the HA globular head domain of the influenza B virus B / Brisbane / 60 / 2008 HA are changed (e.g., substituted) to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA (e.g., A / Vietnam / 1203 / 04 (H5N1) HA; A / mallard / Sweden / 24 / 02 (H8N4) HA; A / shoveler / Netherlands / 18 / 99 (H11N9) HA; orA / black-headed gull / Sweden / 1 / 99 (H13N6) HA). In some embodiments, the amino acid sequence of SEQ ID NO: 24 in the 190 helix of the HA globular head domain of the influenza B virus B / Brisbane / 60 / 2008 HA is changed to the amino acid sequence of SEQ ID NO: 28 or 37. In some embodiments, the HA globular head domain is from influenza B virus B / Phuket / 3073 / 2013 HA and the 190 helix comprises the amino acid sequence of SEQ ID NO: 32 (see also Table 2). In some embodiments, 1, 2, 3, 4, 5, 6, 7, 8, or more amino acid residues in the amino acid sequence of SEQ ID NO: 32 in the 190 helix of the HA globular head domain of the influenza B virus B / Phuket / 3073 / 2013 HA are changed (e.g., substituted) to amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA (e.g., A / Vietnam / 1203 / 04 (H5N1) HA; A / mallard / Sweden / 24 / 02 (H8N4) HA; A / shoveler / Netherlands / 18 / 99 (Hl 1N9) HA; or A / black-headed gull / Sweden / 1 / 99 (H13N6) HA). In some embodiments, the amino acid sequence of SEQ ID NO: 32 in the 190 helix of the HA globular head domain of the influenza B virus B / Phuket / 3073 / 2013 HA is changed to the amino acid sequence of SEQ ID NO: 36. In some embodiments, the 190 helix of the mosaic HA comprises the consensus sequence for the 190 helix in Table 2.

[0123] Table 2

[0124] In some embodiments, provided herein are mosaic HAs comprising an HA ectodomain of influenza B virus B / Yamagata / 16 / 1988 HA, wherein the HA ectodomain comprises (A) an HA stalk domain of the influenza B virus and (B) an HA globular head domain of the influenza B virus with amino acid changes in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain and 0, 1, 2, or 3 compensatory mutations (e.g., compensatory amino acid substitutions) outside of the 120 loop, 150 loop, the 160 loop, and 190 helix, wherein: (i) the amino acid changes in the 120 loop comprise the amino acid sequence TIP and the amino acid sequence of SEQ ID NO: 1 changed to the amino acid sequence FIP and the amino acid sequence of SEQ ID NO: 5, respectively; (ii) the amino acid changes in the 150 loop comprise the amino acid sequence of SEQ ID NO: 2 changed to the amino acid sequence of SEQ ID NO: 6; (iii) the amino acid changes in the 160 loop comprise the amino acid sequence of SEQ ID NO: 3 changed to the amino acid sequence of SEQ ID NO: 7; and (iv) the amino acid changes in the 190 helix comprise the amino acid sequence of SEQ ID NO: 4 changed to the amino acid sequence of SEQ ID NO: 8. In some embodiments, the compensatory mutations (e.g., compensatory amino acid substitutions) comprise E156K. In some embodiments, the mosaic HA further comprises the transmembrane domain or cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises the transmembrane domain and cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises a trimerization domain (e.g., T4 fibritin (foldon) trimerization domain or GCN4- based isoleucine zipper trimerization domain).

[0125] In some embodiments, provided herein are mosaic HAs comprising an HA ectodomain of influenza B virus B / Yamagata / 16 / 1988 HA, wherein the HA ectodomain comprises (A) an HA stalk domain of the influenza B virus and (B) an HA globular head domain of the influenza B virus with amino acid changes in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain and 0, 1, 2, or 3 compensatory mutations (e.g., compensatory amino acid substitutions) outside of the 120 loop, 150 loop, the 160 loop, and 190 helix, wherein: (i) the amino acid changes in the 120 loop comprise the amino acid sequence TIP and the amino acid sequence of SEQ ID NO: 1 changed to the amino acid sequence HIP and the amino acid sequence of SEQ ID NO: 9, respectively; (ii) the amino acid changes in the 150 loop comprise the amino acid sequence of SEQ ID NO: 2 changed to the amino acid sequence of SEQ ID NO: 10; (iii) the amino acid changes in the 160 loop comprise the amino acid sequence of SEQ ID NO: 3 changed to the amino acid sequence of SEQ ID NO: 11; and (iv) the amino acid changes in the 190 helix comprise the amino acidsequence of SEQ ID NO: 4 changed to the amino acid sequence of SEQ ID NO: 12. In some embodiments, the compensatory mutations (e.g., compensatory amino acid substitutions) comprise E156K. In some embodiments, the mosaic HA further comprises the transmembrane domain or cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises the transmembrane domain and cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises a trimerization domain (e.g., T4 fibritin (foldon) trimerization domain or GCN4- based isoleucine zipper trimerization domain).

[0126] In some embodiments, provided herein are mosaic HAs comprising an HA ectodomain of influenza B virus B / Yamagata / 16 / 1988 HA, wherein the HA ectodomain comprises (A) an HA stalk domain of the influenza B virus and (B) an HA globular head domain of the influenza B virus with amino acid changes in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain and 0, 1, 2, or 3 compensatory mutations (e.g., compensatory amino acid substitutions) outside of the 120 loop, 150 loop, the 160 loop, and 190 helix, wherein: (i) the amino acid changes in the 120 loop comprise the amino acid sequence TIP and the amino acid sequence of SEQ ID NO: 1 changed to the amino acid sequence LIP and the amino acid sequence of SEQ ID NO: 13, respectively; (ii) the amino acid changes in the 150 loop comprise the amino acid sequence of SEQ ID NO: 2 changed to the amino acid sequence of SEQ ID NO: 14; (iii) the amino acid changes in the 160 loop comprise the amino acid sequence of SEQ ID NO: 3 changed to the amino acid sequence of SEQ ID NO: 115 and (iv) the amino acid changes in the 190 helix comprise the amino acid sequence of SEQ ID NO: 4 changed to the amino acid sequence of SEQ ID NO: 15. In some embodiments, the compensatory mutations (e.g., compensatory amino acid substitutions) comprise G252E. In some embodiments, the mosaic HA further comprises the transmembrane domain or cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises the transmembrane domain and cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises a trimerization domain (e.g., T4 fibritin (foldon) trimerization domain or GCN4- based isoleucine zipper trimerization domain).

[0127] In some embodiments, provided herein are mosaic HAs comprising an HA ectodomain of influenza B virus B / Yamagata / 16 / 1988 HA, wherein the HA ectodomain comprises (A) an HA stalk domain of the influenza B virus and (B) an HA globular head domain of the influenza B virus with amino acid changes in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain and 0, 1, 2, or 3 compensatory mutations (e.g.,compensatory amino acid substitutions) outside of the 120 loop, 150 loop, the 160 loop, and 190 helix, wherein: (i) the amino acid changes in the 120 loop comprise the amino acid sequence TIP and the amino acid sequence of SEQ ID NO: 1 changed to the amino acid sequence NIP and the amino acid sequence of SEQ ID NO: 17, respectively; (ii) the amino acid changes in the 150 loop comprise the amino acid sequence of SEQ ID NO: 2 changed to the amino acid sequence of SEQ ID NO: 18; (iii) the amino acid changes in the 160 loop comprise the amino acid sequence of SEQ ID NO: 3 changed to the amino acid sequence of SEQ ID NO: 19; and (iv) the amino acid changes in the 190 helix comprise the amino acid sequence of SEQ ID NO: 4 changed to the amino acid sequence of SEQ ID NO: 20. In some embodiments, the compensatory mutations (e.g., compensatory amino acid substitutions) comprise E156K. In some embodiments, the mosaic HA further comprises the transmembrane domain or cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises the transmembrane domain and cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises a trimerization domain (e.g., T4 fibritin (foldon) trimerization domain or GCN4- based isoleucine zipper trimerization domain).

[0128] In some embodiments, provided herein are mosaic HAs comprising an HA ectodomain of influenza B virus B / Brisbane / 60 / 2008 HA, wherein the HA ectodomain comprises (A) an HA stalk domain of the influenza B virus and (B) an HA globular head domain of the influenza B virus with amino acid changes in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain and 0, 1, 2, or 3 compensatory mutations (e.g., compensatory amino acid substitutions) outside of the 120 loop, 150 loop, the 160 loop, and 190 helix, wherein: (i) the amino acid changes in the 120 loop comprise the amino acid sequence KIP and the amino acid sequence of SEQ ID NO: 21 changed to the amino acid sequence NIP and the amino acid sequence of SEQ ID NO: 25, respectively; (ii) the amino acid changes in the 150 loop comprise the amino acid sequence of SEQ ID NO: 22 changed to the amino acid sequence of SEQ ID NO: 26; (iii) the amino acid changes in the 160 loop comprise the amino acid sequence of SEQ ID NO: 23 changed to the amino acid sequence of SEQ ID NO: 27; and (iv) the amino acid changes in the 190 helix comprise the amino acid sequence of SEQ ID NO: 24 changed to the amino acid sequence of SEQ ID NO: 28 or 37. In some embodiments, the compensatory mutations (e.g., compensatory amino acid substitutions) comprise G156K. In some embodiments, the mosaic HA further comprises the transmembrane domain or cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises the transmembrane domain and cytoplasmicdomain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises a trimerization domain (e.g., T4 fibritin (foldon) trimerization domain or GCN4- based isoleucine zipper trimerization domain).

[0129] In some embodiments, provided herein are mosaic HAs comprising an HA ectodomain of influenza B virus B / Phuket / 3073 / 2013 HA, wherein the HA ectodomain comprises (A) an HA stalk domain of the influenza B virus and (B) an HA globular head domain of the influenza B virus with amino acid changes in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain and 0, 1, 2, or 3 compensatory mutations (e.g., compensatory amino acid substitutions) outside of the 120 loop, 150 loop, the 160 loop, and 190 helix, wherein: (i) the amino acid changes in the 120 loop comprise the amino acid sequence TTP and the amino acid sequence of SEQ ID NO: 29 changed to the amino acid sequence FTP and the amino acid sequence of SEQ ID NO: 33, respectively; (ii) the amino acid changes in the 150 loop comprise the amino acid sequence of SEQ ID NO: 30 changed to the amino acid sequence of SEQ ID NO: 34; (iii) the amino acid changes in the 160 loop comprise the amino acid sequence of SEQ ID NO: 31 changed to the amino acid sequence of SEQ ID NO: 35; and (iv) the amino acid changes in the 190 helix comprise the amino acid sequence of SEQ ID NO: 32 changed to the amino acid sequence of SEQ ID NO: 36. In some embodiments, the compensatory mutations (e.g., compensatory amino acid substitutions) comprise G156K. In some embodiments, the mosaic HA further comprises the transmembrane domain or cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises the transmembrane domain and cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises a trimerization domain (e.g., T4 fibritin (foldon) trimerization domain or GCN4- based isoleucine zipper trimerization domain).

[0130] The amino acid residues in the globular head domain of an influenza A virus HA in a region corresponding to an antigenic site (e.g., 120 loop, 150 loop, 160 loop and / or 190 helix) in the globular head domain of an influenza B virus HA may be identified using techniques known to one skilled in the art. In specific embodiments, the amino acid residues in the globular head domain of an influenza A virus HA in a region corresponding to an antigenic site (e.g., 120 loop, 150 loop, 160 loop and / or 190 helix) in the globular head domain of an influenza B virus HA are identified by comparing the amino acid sequences and / or structural information (e.g., crystal structures) of HA of influenza A viruses and influenza B viruses. In particular embodiments, alignments of the amino acid sequences of HA of influenza A viruses and influenza B viruses as well as assessing the viruses forstructural similarity enables the skilled person in the art to select the amino acid residues in the influenza B virus HA antigenic site to change (e.g., substitute, delete, and / or add) to amino acid residues in a corresponding region in the globular head domain of an influenza A virus HA. For example, one might want to refrain from changing (e.g., substituting and / or deleting) amino acid residues, such as cysteine, proline or both, in the influenza B virus HA antigenic site that may impact the folding of the mosaic HA with amino acid residues from a corresponding region in the globular head domain of an influenza A virus HA. In addition, one might want to refrain from changing (e.g., substituting and / or deleting) amino acid residues in the influenza B virus HA antigenic site that impact the coding for N-linked glycosylation sites (N-X-S / T). In selecting the amino acid residues to change (e.g., substitute, delete, and / or add), care should be taken to maintain the conformation / structure of the HA. In some embodiments, amino acid residues that are highly conserved in an antigenic site of the globular head domain of influenza B virus HAs, one might want to refrain from changing (e.g., substituting and / or deleting) to amino acid residues from a corresponding region in the globular head domain of an influenza A virus HA. For example, those amino acid residues identified by Wang et al., 2008, Journal of Virology 82: 3011-3020 as being variant among HAs of influenza B viruses may be selected as amino acid residues within an antigenic site of the globular head domain of an influenza B virus HA to change (e.g., substitute) to other amino acid residues (e.g., other amino acid residues from a corresponding region of the globular head domain of an influenza A virus HA), while those highly conserved amino acid residues within the antigenic site of the globular head domain of an influenza B virus HA may not be changed (e.g., substituted). In a specific embodiment, when amino acid residues that are highly conserved in an antigenic site of the globular head domain of influenza B virus HAs, one might want to refrain from changing (e.g., substituting and / or deleting) amino acid residues in the antigenic site of the globular head domain of an influenza B virus HA with amino acid residues from a corresponding region in the globular head domain of an influenza A virus HA. For example, one of skill in the art may not want to substitute the methionine in the 190 helix of an influenza B virus with another amino acid residue. In some embodiments, with respect to amino acid residues such as proline found in an antigenic site of the globular head domain of an influenza B virus HA, one might want to refrain from substituting with amino acid residues from a corresponding region in the globular head domain of an influenza A virus HA. In some embodiments, with respect to amino acid residues such as cysteine, proline or both found in an antigenic site of the globular head domain of an influenza B virus HA, one might want to refrain from substituting with amino acid residues from acorresponding region in the globular head domain of an influenza A virus HA. In some embodiments, one might want to refrain from substituting amino acid residues such as proline found in an antigenic site of the globular head domain of an influenza B virus HA with amino acid residues from a corresponding region in the globular head domain of an influenza A virus HA. In specific embodiments, the amino acid residues substituted in an antigenic site of the globular head domain of an influenza B virus are not consecutive amino acid residues. For example, amino acid residues that are found conformationally close to one another may be substituted for other amino acid residues. In other embodiments, the amino acid residues substituted in an antigenic site of the globular head domain of an influenza B virus are consecutive amino acid residues. In some embodiments, an amino acid residue found in the antigenic site of an influenza B virus is substituted with a conservative amino acid residue (z.e., a conservative substitution). In some embodiments, random amino acid changes are introduced into an antigenic site (e.g., 120 loop, 150 loop, 160 loop, and / or 190 helix) provided they do not impact the folding / conformation / structure of the HA. In some embodiments, one or more irrelevant epitopes are introduced into an antigenic site (e.g., 120 loop, 150 loop, 160 loop, and / or 190 helix) provided they do not impact the folding / conformation / structure of the HA. The effect of amino acid changes (e.g., substitutions, deletions, and / or additions) on the conformation / structure may be determined by assays known to one of skill in the art, e.g., structure programs, crystallography, or functional assays. See, e.g., Section 5.6, infra, and Section 6, infra. In a particular embodiment, the mosaic HA polypeptides may be evaluated for antigenic conservation using a panel of monoclonal antibodies that bind to conserved epitopes in the globular head domain of HA and the stem domain of HA. In a specific embodiment, the methods described herein or in Sun et al., 2019, J Virol. 93(12): e00333-19 or Liu et al., 2021, Front. Immunol., 12: 746447, are used to evaluate antigenic conservation of the mosaic HA. In addition, the mosaic HA polypeptides described herein may be evaluated to determine whether the antigenic sites of the influenza B virus HA were mutated using techniques known to one of skill in the art or described herein (see, e.g., Section 6, infra, including the HI assay described therein). In particular, the mosaic HA polypeptides described herein may be evaluated to determine if the amino acid changes (e.g., substitutions, deletions, and / or additions) in the antigenic site(s) of the influenza B virus HA result in loss of a variable region(s) of the influenza B virus HA using techniques known to one of skill in the art or described herein (see, e.g., Section 6, infra, including the HI assay described therein). In a specific embodiment, the mosaic HA polypeptides described herein may be evaluated to determine ifthe amino acid changes (e.g., substitutions, deletions, and / or additions) in the antigenic site(s) of the influenza B virus HA reduce or eliminate the immunodominant epitopes of the influenza B virus HA using techniques known to one of skill in the art or described herein (see, e.g., Section 6, infra, including the HI assay described therein). In a specific embodiment, a mosaic HA polypeptide described herein is assessed in an HI assay, such as described in Section 6, infra, to evaluate the replacement of the antigenic site(s) in the influenza B virus HA.

[0131] In some embodiments, amino acid residues in an antigenic site of an influenza B virus HA may be changed (e.g., substituted) to amino acid residues in an antigenic site of a group 1 or a group 2 influenza A virus HA. Antigenic sites in a group 1 influenza A virus HA include Sa, Sb, Cal, Ca2, and Cb. Antigenic sites in a group 2 influenza A virus HA include A, B, C, D, and E. In some embodiments, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more amino acid residues in 120 loop of an influenza B virus HA are substituted with 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more amino acid residues in site E of the globular head domain of an influenza A virus H3 HA. In some embodiments, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more amino acid residues in 120 loop of an influenza B virus HA are substituted with 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more amino acid residues in site Sa of the globular head domain of an influenza A virus Hl HA. In some embodiments, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more amino acid residues in 120 loop of an influenza B virus HA are substituted with 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more amino acid residues in site Cb of the globular head domain of an influenza A virus Hl HA. In some embodiments, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more amino acid residues in 120 loop of an influenza B virus HA are substituted with 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more amino acid residues in sites Sa and / or Cb of the globular head domain of an influenza A virus Hl HA.

[0132] In some embodiments, 1, 2, 3, 4, 5, 6, 7, 8, or more amino acid residues in 150 loop of an influenza B virus HA are substituted with 1, 2, 3, 4, 5, 6, 7, 8, or more amino acid residues in site A of the globular head domain of an influenza A virus H3 HA. In some embodiments, 1, 2, 3, 4, 5, 6, 7, 8, or more amino acid residues in 150 loop of an influenza B virus HA are substituted with 1, 2, 3, 4, 5, 6, 7, 8, or more amino acid residues in site Ca of the globular head domain of an influenza A virus Hl HA.

[0133] In some embodiments, 1, 2, 3, 4, 5 or more amino acid residues in 160 loop of an influenza B virus HA are substituted with 1, 2, 3, 4, 5 or more amino acid residues in site B of the globular head domain of an influenza A virus H3 HA. In some embodiments, 1, 2, 3, 4, 5 or more amino acid residues in 160 loop of an influenza B virus HA are substituted with 1, 2, 3, 4, 5 or more amino acid residues in site Sa of the globular head domain of an influenza A virus Hl HA.

[0134] In some embodiments, 1, 2, 3, 4, 5, 6, 7, 8 or more amino acid residues in 190 helix of an influenza B virus HA are substituted with 1, 2, 3, 4, 5, 6, 7, 8 or more amino acid residues in site B of the globular head domain of an influenza A virus H3 HA. In some embodiments, 1, 2, 3, 4, 5, 6, 7, 8 or more amino acid residues in 190 helix of an influenza B virus HA are substituted with 1, 2, 3, 4, 5, 6, 7, 8 or more amino acid residues in site Sb of the globular head domain of an influenza A virus Hl HA.

[0135] In a specific embodiment, the influenza A virus HA utilized in the generation of a mosaic HA polypeptide described herein is the HA from an influenza virus of the Hl, H2, H3, H4, H5, H6, H7, H8, H9, H10, Hl l, H12, H13, H14, H15, H16, H17, or H18 subtype. In a specific embodiment, the influenza A virus HA utilized in the generation of a mosaic HA polypeptide described herein is the HA from an influenza virus of the H2, H4, H5, H6, H7, H8, H9, H10, H11, H12, H13, H14, H15, H16, H17, or H18 subtype. In a specific embodiment, the influenza A virus HA utilized in the generation of a mosaic HA polypeptide described herein is the HA from an influenza virus of the H5, H8, Hl l, H12, or H13 subtype. In a specific embodiment, the influenza A virus HA utilized in the generation of a mosaic HA polypeptide described herein is the HA from an influenza virus of the H5 subtype. In a specific embodiment, the influenza A virus HA utilized in the generation of a mosaic HA polypeptide described herein is the HA from an influenza virus of the H8 subtype. In a specific embodiment, the influenza A virus HA utilized in the generation of a mosaic HA polypeptide described herein is the HA from an influenza virus of the Hl 1 subtype. In a specific embodiment, the influenza A virus HA utilized in the generation of a mosaic HA polypeptide described herein is the HA from an influenza virus of the H12 subtype. In a specific embodiment, the influenza A virus HA utilized in the generation of a mosaic HA polypeptide described herein is the HA from an influenza virus of the Hl 3 subtype. In a specific embodiment, the influenza A virus HA utilized in the generation of a mosaic HA polypeptide described herein is the HA from an avian influenza virus. In specific embodiments, the influenza A virus HA utilized in the generation of a mosaic HA polypeptide described herein is the HA from an influenza A virus to which a subject (e.g., ahuman subject is naive). In some embodiments, the influenza A virus HA utilized in the generation of a mosaic HA polypeptide described herein is the HA from an exotic influenza A virus HA. In a specific embodiment, the influenza A virus HA utilized in the generation of a mosaic HA polypeptide described herein is the HA from an exotic avian influenza A virus HA.

[0136] Non-limiting examples of influenza A viruses include subtype H10N4, subtype H10N5, subtype H10N7, subtype H10N8, subtype H10N9, subtype Hl INI, subtype Hl 1N13, subtype Hl 1N2, subtype Hl 1N4, subtype Hl 1N6, subtype Hl 1N8, subtype H11N9, subtype H12N1, subtype H12N4, subtype Hl 2N5, subtype H12N8, subtype H13N2, subtype H13N3, subtype H13N6, subtype H13N7, subtype H14N5, subtype H14N6, subtype H15N8, subtype H15N9, subtype H16N3, subtype H1N1, subtype H1N2, subtype H1N3, subtype H1N6, subtype H1N9, subtype H2N1, subtype H2N2, subtype H2N3, subtype H2N5, subtype H2N7, subtype H2N8, subtype H2N9, subtype H3N1, subtype H3N2, subtype H3N3, subtype H3N4, subtype, H3N5, subtype H3N6, subtype H3N8, subtype H3N9, subtype H4N1, subtype H4N2, subtype H4N3, subtype H4N4, subtype H4N5, subtype H4N6, subtype H4N8, subtype H4N9, subtype H5N1, subtype H5N2, subtype H5N3, subtype H5N4, subtype H5N6, subtype H5N7, subtype H5N8, subtype H5N9, subtype H6N1, subtype H6N2, subtype H6N3, subtype H6N4, subtype H6N5, subtype H6N6, subtype H6N7, subtype H6N8, subtype H6N9, subtype H7N1, subtype H7N2, subtype H7N3, subtype H7N4, subtype H7N5, subtype H7N7, subtype H7N8, subtype H7N9, subtype H8N4, subtype H8N5, subtype H9N1, subtype H9N2, subtype H9N3, subtype H9N5, subtype H9N6, subtype H9N7, subtype H9N8, and subtype H9N9.

[0137] Specific examples of strains of influenza A virus include, but are not limited to: A / Victoria / 361 / 2011 (H3N2); A / California / 4 / 2009 (H1N1); A / California / 7 / 2009 (H1N1); A / Perth / 16 / 2009 (H3N2); A / Brisbane / 59 / 2007 (H1N1); A / Brisbane / 10 / 2007 ((H3N2); A / sw / Iowa / 15 / 30 (H1N1); A / WSN / 33 (H1N1); A / eq / Prague / 1 / 56 (H7N7); A / PR / 8 / 34; A / mallard / Potsdam / 178-4 / 83 (H2N2); A / herring gull / DE / 712 / 88 (H16N3); A / sw / Hong Kong / 168 / 1993 (H1N1); A / mallard / Alberta / 211 / 98 (H1N1); A / shorebird / Delaware / 168 / 06 (H16N3); A / sw / Netherlands / 25 / 80 (H1N1); A / sw / Germany / 2 / 81 (H1N1); A / sw / Hannover / 1 / 81 (H1N1); A / sw / Potsdam / 1 / 81 (H1N1); A / sw / Potsdam / 15 / 81 (H1N1); A / sw / Potsdam / 268 / 81 (H1N1); A / sw / Finistere / 2899 / 82 (H1N1); A / sw / Potsdam / 35 / 82 (H3N2); A / sw / Cote d'Armor / 3633 / 84 (H3N2); A / sw / Gent / 1 / 84 (H3N2);A / sw / Netherlands / 12 / 85 (H1N1); A / sw / Karrenzien / 2 / 87 (H3N2); A / sw / Schwerin / 103 / 89 (H1N1); A / turkey / Germany / 3 / 91 (H1N1); A / sw / Germany / 8533 / 91 (H1N1);A / sw / Belgium / 220 / 92 (H3N2); A / sw / Gent / V230 / 92 (H1N1); A / sw / Leipzig / 145 / 92 (H3N2); A / sw / Re220 / 92hp (H3N2); A / sw / Bakum / 909 / 93 (H3N2); A / sw / Schleswig-Holstein / 1 / 93 (H1N1); A / sw / Scotland / 419440 / 94 (H1N2); A / sw / Bakum / 5 / 95 (H1N1); A / sw / Best / 5C / 96 (H1N1); A / sw / England / 17394 / 96 (H1N2); A / sw / Jena / 5 / 96 (H3N2); A / sw / Oedenrode / 7C / 96 (H3N2); A / sw / Lohne / 1 / 97 (H3N2); A / sw / Cote d'Armor / 790 / 97 (H1N2);A / sw / Bakum / 1362 / 98 (H3N2); A / sw / Italy / 1521 / 98 (H1N2); A / sw / Italy / 1553-2 / 98 (H3N2); A / sw / Italy / 1566 / 98 (H1N1); A / sw / Italy / 1589 / 98 (H1N1); A / sw / Bakum / 8602 / 99 (H3N2); A / sw / Cotes d'Armor / 604 / 99 (H1N2); A / sw / Cote d'Armor / 1482 / 99 (H1N1);A / sw / Gent / 7625 / 99 (H1N2); A / Hong Kong / 1774 / 99 (H3N2); A / sw / Hong Kong / 5190 / 99 (H3N2); A / sw / Hong Kong / 5200 / 99 (H3N2); A / sw / Hong Kong / 5212 / 99 (H3N2); A / sw / Ille et Villaine / 1455 / 99 (H1N1); A / sw / Italy / 1654- 1 / 99 (H1N2); A / sw / Italy / 2034 / 99 (H1N1);A / sw / Italy / 2064 / 99 (H1N2); A / sw / Berlin / 1578 / 00 (H3N2); A / sw / Bakum / 1832 / 00 (H1N2);A / sw / Bakum / 1833 / 00 (H1N2); A / sw / Cote d'Armor / 800 / 00 (H1N2); A / sw / Hong Kong / 7982 / 00 (H3N2); A / sw / Italy / 1081 / 00 (H1N2); A / sw / Belzig / 2 / 01 (H1N1); A / sw / Belzig / 54 / 01 (H3N2); A / sw / Hong Kong / 9296 / 01 (H3N2); A / sw / Hong Kong / 9745 / 01 (H3N2); A / sw / Spain / 33601 / 01 (H3N2); A / sw / Hong Kong / 1144 / 02 (H3N2); A / sw / Hong Kong / 1197 / 02 (H3N2); A / sw / Spain / 39139 / 02 (H3N2); A / sw / Spain / 42386 / 02 (H3N2);A / Switzerland / 8808 / 2002 (H1N1); A / sw / Bakum / 1769 / 03 (H3N2);A / sw / Bissendorf / IDTl 864 / 03 (H3N2); A / sw / Ehren / IDT2570 / 03 (H1N2); A / sw / Gescher / IDT2702 / 03 (H1N2); A / sw / Haselunne / 2617 / 03 hp (H1N1); A / sw / Loningen / IDT2530 / 03 (H1N2); A / sw / IVD / IDT2674 / 03 (H1N2); A / sw / Nordkirchen / IDT 1993 / 03 (H3N2); A / sw / Nordwalde / IDT2197 / 03 (H1N2);A / sw / Norden / IDT2308 / 03 (H1N2); A / sw / Spain / 50047 / 03 (H1N1); A / sw / Spain / 51915 / 03 (H1N1); A / sw / Vechta / 2623 / 03 (H1N1); A / sw / Visbek / IDT2869 / 03 (H1N2);A / sw / Waltersdorf / IDT2527 / 03 (H1N2); A / sw / Damme / IDT2890 / 04 (H3N2); A / sw / Geldem / IDT2888 / 04 (H1N1); A / sw / Granstedt / IDT3475 / 04 (H1N2); A / sw / Greven / IDT2889 / 04 (H1N1); A / sw / Gudensberg / IDT2930 / 04 (H1N2); A / sw / Gudensberg / IDT2931 / 04 (H1N2); A / sw / Lohne / IDT3357 / 04 (H3N2); A / sw / Nortrup / IDT3685 / 04 (H1N2); A / sw / Seesen / IDT3055 / 04 (H3N2);A / sw / Spain / 53207 / 04 (H1N1); A / sw / Spain / 54008 / 04 (H3N2); A / sw / Stolzenau / IDT3296 / 04 (H1N2); A / sw / Wedel / IDT2965 / 04 (H1N1); A / sw / Bad Griesbach / IDT4191 / 05 (H3N2); A / sw / Cloppenburg / IDT4777 / 05 (H1N2); A / sw / Dotlingen / IDT3780 / 05 (H1N2);A / sw / Dotlingen / IDT4735 / 05 (H1N2); A / sw / Egglham / IDT5250 / 05 (H3N2); A / sw / Harkenblek / IDT4097 / 05 (H3N2); A / sw / Hertzen / IDT4317 / 05 (H3N2);A / sw / Krogel / IDT4192 / 05 (H1N1); A / sw / Laer / IDT3893 / 05 (H1N1); A / sw / Laer / IDT4126 / 05 (H3N2); A / sw / Merzen / IDT4114 / 05 (H3N2); A / sw / Muesleringen-S. / IDT4263 / 05 (H3N2); A / sw / Osterhofen / IDT4004 / 05 (H3N2); A / sw / Sprenge / IDT3805 / 05 (H1N2);A / sw / Stadtlohn / IDT3853 / 05 (H1N2); A / sw / Voglarn / IDT4096 / 05 (H1N1); A / sw / Wohlerst / IDT4093 / 05 (H1N1); A / sw / Bad Griesbach / IDT5604 / 06 (H1N1); A / sw / Herzlake / IDT5335 / 06 (H3N2); A / sw / Herzlake / IDT5336 / 06 (H3N2);A / sw / Herzlake / IDT5337 / 06 (H3N2); and A / wild boar / Germany / Rl 69 / 2006 (H3N2).

[0138] Other specific examples of strains of influenza A virus include, but are not limited to: A / Toronto / 3141 / 2009 (H1N1); A / Regensburg / D6 / 2009 (H1N1); A / Bayern / 62 / 2009 (H1N1); A / Bayem / 62 / 2009 (H1N1); A / Bradenburg / 19 / 2009 (H1N1); A / Bradenburg / 20 / 2009 (H1N1); A / Distrito Federal / 2611 / 2009 (H1N1); A / Mato Grosso / 2329 / 2009 (H1N1); A / Sao Paul o / l 454 / 2009 (H1N1); A / Sao Paulo / 2233 / 2009 (H1N1); A / Stockholm / 37 / 2009 (H1N1); A / Stockholm / 41 / 2009 (H1N1); A / Stockholm / 45 / 2009 (H1N1); A / swine / Alberta / OTH-33- 1 / 2009 (H1N1); A / swine / Alberta / OTH-33- 14 / 2009 (H1N1); A / swine / Alberta / OTH-33- 2 / 2009 (H1N1); A / swine / Alberta / OTH-33-21 / 2009 (H1N1); A / swine / Alberta / OTH-33- 22 / 2009 (H1N1); A / swine / Alberta / OTH-33 -23 / 2009 (H1N1); A / swine / Alberta / OTH-33- 24 / 2009 (H1N1); A / swine / Alberta / OTH-33 -25 / 2009 (H1N1); A / swine / Alberta / OTH-33- 3 / 2009 (H1N1); A / swine / Alberta / OTH-33 -7 / 2009 (H1N1); A / Beijing / 502 / 2009 (H1N1);A / Firenze / 10 / 2009 (H1N1); A / Hong Kong / 2369 / 2009 (H1N1); A / Italy / 85 / 2009 (H1N1); A / Santo Domingo / 572N / 2009 (H1N1); A / Catalonia / 385 / 2009 (H1N1);A / Catalonia / 386 / 2009 (H1N1); A / Catalonia / 387 / 2009 (H1N1); A / Catalonia / 390 / 2009 (H1N1); A / Catalonia / 394 / 2009 (HlNl);A / Catalonia / 397 / 2009 (H1N1);A / Catalonia / 398 / 2009 (H1N1); A / Catalonia / 399 / 2009 (H1N1); A / Sao Paulo / 2303 / 2009 (H1N1); A / Akita / 1 / 2009 (H1N1); A / Castro / JXP / 2009 (H1N1); A / Fukushima / 1 / 2009 (H1N1); A / Israel / 276 / 2009 (H1N1); A / Israel / 277 / 2009 (H1N1); A / Israel / 70 / 2009 (H1N1); A / Iwate / 1 / 2009 (H1N1); A / Iwate / 2 / 2009 (H1N1); A / Kagoshima / 1 / 2009 (H1N1);A / Osaka / 180 / 2009 (H1N1); A / Puerto Montt / Bio87 / 2009 (Hl Nl); A / Sao Paulo / 2303 / 2009 (H1N1); A / Sapporo / 1 / 2009 (H1N1); A / Stockholm / 30 / 2009 (H1N1); A / Stockholm / 31 / 2009 (H1N1); A / Stockholm / 32 / 2009 (H1N1); A / Stockholm / 33 / 2009 (H1N1);A / Stockholm / 34 / 2009 (H1N1); A / Stockholm / 35 / 2009 (H1N1); A / Stockholm / 36 / 2009 (H1N1); A / Stockholm / 38 / 2009 (H1N1); A / Stockholm / 39 / 2009 (H1N1);A / Stockholm / 40 / 2009 (H1N1;) A / Stockholm / 42 / 2009 (H1N1); A / Stockholm / 43 / 2009 (H1N1); A / Stockholm / 44 / 2009 (H1N1); A / Utsunomiya / 2 / 2009 (H1N1);A / WRAIR / 0573N / 2009 (H1N1); and A / Zhejiang / DTID-ZJU01 / 2009 (H1N1).

[0139] In some embodiments, the influenza A virus HA utilized in the generation of a mosaic HA polypeptide described herein is the HA from influenzaA / mallard / Sweden / 24 / 2002 virus (GenBank Accession No. CY060249.1; GenBank GI No. 294441479). In a specific embodiment, the influenza A virus HA utilized in the generation of a mosaic HA polypeptide described herein is the HA from influenza A / Vietnam / 1203 / 04 virus (GenBank Accession No. EF541403.1; GenBank GI No. 145284465; and Steel et al., 2009, Journal of Virology, 83(4): 1742-1753 for the HA of influenza A / Vietnam / 1203 / 04 (HALo) virus). In a specific embodiment, the influenza A virus HA utilized in the generation of a mosaic HA polypeptide described herein is the HA from influenza A / northern shoveler / Netherlands / 18 / 99 virus (GenBank Accession No. CY060417.1; GenBank GI No. 294441876). In a specific embodiment, the influenza A virus HA utilized in the generation of a mosaic HA polypeptide described herein is the HA from influenza A / mallard interior Alaska_7MP0167_2007 virus (GenBank Accession No. CY077198.1; GenBank GI No.312652817). In a specific embodiment, the influenza A virus HA utilized in the generation of a mosaic HA polypeptide described herein is the HA from influenza A / Puerto Rico / 8 / 34 virus (GenBank Accession No. AF389118.1; GenBank GI No. 21693168). In a specific embodiment, the influenza A virus HA utilized in the generation of a mosaic HA polypeptide described herein is the HA from influenza A / black headed gull / Sweden / 1 / 99 (GenBank Accession No. AY684887.1).

[0140] In a specific embodiment, the influenza B virus HA utilized in the generation of a mosaic HA polypeptide described herein is an HA from an influenza B virus of the Yamagata lineage. In a specific embodiment, the influenza B virus HA utilized in the generation of a mosaic HA polypeptide described herein is an HA from an influenza B virus of the Victoria lineage. In some embodiments, the influenza B virus HA utilized in the generation of a mosaic HA polypeptide described herein is the HA from influenza B virus disclosed herein (e.g., in Section 5.4, or Example 1). In some embodiments, the influenza B virus HA utilized in the generation of a mosaic HA polypeptide described herein is the HA from influenza B virus disclosed in FIG. 1G or 1H. In a specific embodiment, the influenza B virus HA utilized in the generation of a mosaic HA polypeptide described herein is the HA from influenza B / Yamagata / 16 / 1988 virus. In a specific embodiment, the influenza B virus HA utilized in the generation of a mosaic HA polypeptide described herein is the HA from influenza B / Phuket / 3073 / 2013 virus. In a specific embodiment, the influenza B virus HA utilized in the generation of a mosaic HA polypeptide described herein is the HA from influenza B / Brisbane / 60 / 2008. In a specific embodiment, the influenza B virus HA utilizedin the generation of a mosaic HA polypeptide described herein is the HA from an influenza B / Malaysia / 2506 / 04 mouse adapted (MA) virus. In a specific embodiment, the influenza B virus HA utilized in the generation of a mosaic HA polypeptide described herein is the HA from influenza B / Malaysia / 2506 / 04 virus (see, e.g., GenBank Accession No. CY040449.1).

[0141] In a specific embodiment, a mosaic HA polypeptide is a mosaic HA polypeptide described in Section 6, infra. In a specific embodiment, a mosaic HA polypeptide comprises the amino acid sequence of the mosaic HA polypeptide in Table 3. In another specific embodiment, a mosaic HA polypeptide comprises the amino acid sequence of the mosaic HA polypeptide in Table 3 without the signal peptide. In another specific embodiment, a mosaic HA polypeptide comprises the amino acid sequences of the ectodomain of the mosaic HA polypeptide in Table 3.

[0142] In a specific embodiment, the influenza B virus HA sequence utilized to generate a mosaic HA polypeptide described herein is the HA sequence from an influenza B virus disclosed in Section 5.4, infra. In a specific embodiment, the influenza B virus HA sequence utilized to generate a mosaic HA polypeptide described herein is the HA sequence from an influenza B virus disclosed in Section 6, infra. In a specific embodiment, the influenza A virus HA sequence utilized to generate a mosaic HA polypeptide described herein is the HA sequence from an influenza A virus disclosed herein (e.g., in Section 6, infra). For example, the influenza A virus HA may be from a group 1 or a group 2 virus. Group 1 influenza A viruses include Hl, H2, H6, H8, H9, Hl l, H12, H13, H16, H17, and H18. Group 1 influenza A viruses include H3, H4, H7, H10, H14, and H15. In specific embodiments, the influenza A virus HA is from an Hl, H2, H3, H4, H5, H6, H7, H8, H9, H10, Hl l, H12, H13, H14, H15, Hl 6, Hl 7, or Hl 8 influenza A virus.

[0143] In some embodiments, provided herein are mosaic HA polypeptides comprising an HA ectodomain of an influenza B virus HA, wherein the HA ectodomain comprises the HA stalk domain of the influenza B virus HA and the HA globular head domain of the influenza B virus HA with amino acid changes in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain, wherein the influenza B virus HA is influenza B virus B / Yamagata / 16 / 1988 HA, wherein: (i) the amino acid changes in the 120 loop substitute the amino acid sequence TIP and the amino acid sequence of SEQ ID NO: 1 with the amino acid sequence FIP and the amino acid sequence of SEQ ID NO: 5, respectively; (ii) the amino acid changes in the 150 loop substitute the amino acid sequence of SEQ ID NO: 2 with the amino acid sequence of SEQ ID NO: 6; (iii) the amino acid changes in the 160 loop substitute the amino acid sequence of SEQ ID NO: 3 with the amino acid sequence of SEQ ID NO: 7; and(iv) the amino acid changes in the 190 helix substitute the amino acid sequence of SEQ ID NO: 4 with the amino acid sequence of SEQ ID NO: 8. In some embodiments, the HA ectodomain further comprises 1, 2, or 3 compensatory mutations (e.g., compensatory amino acid substitutions) outside the 120 loop, 150 loop, 160 loop, and 190 helix (e.g., E156K). In some embodiments, the mosaic HA further comprises the transmembrane domain or cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises the transmembrane domain and cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises a trimerization domain (e.g., T4 fibritin (foldon) trimerization domain or GCN4-based isoleucine zipper trimerization domain).

[0144] In some embodiments, provided herein are mosaic HA polypeptides comprising an HA ectodomain of an influenza B virus HA, wherein the HA ectodomain comprises the HA stalk domain of the influenza B virus HA and the HA globular head domain of the influenza B virus HA with amino acid changes in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain, wherein the influenza B virus HA is influenza B virus B / Yamagata / 16 / 1988 HA, wherein: (i) the amino acid changes in the 120 loop substitute the amino acid sequence TIP and the amino acid sequence of SEQ ID NO: 1 with the amino acid sequence HIP and the amino acid sequence of SEQ ID NO: 9, respectively; (ii) the amino acid changes in the 150 loop substitute the amino acid sequence of SEQ ID NO: 2 with the amino acid sequence of SEQ ID NO: 10; (iii) the amino acid changes in the 160 loop substitute the amino acid sequence of SEQ ID NO: 3 with the amino acid sequence of SEQ ID NO: 11; and (iv) the amino acid changes in the 190 helix substitute the amino acid sequence of SEQ ID NO: 4 with the amino acid sequence of SEQ ID NO: 12. In some embodiments, the HA ectodomain further comprises 1, 2, or 3 compensatory amino acid substitutions outside the 120 loop, 150 loop, 160 loop, and 190 helix (e.g., E156K). In some embodiments, the mosaic HA further comprises the transmembrane domain or cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises the transmembrane domain and cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises a trimerization domain (e.g., T4 fibritin (foldon) trimerization domain or GCN4-based isoleucine zipper trimerization domain).

[0145] In some embodiments, provided herein are mosaic HA polypeptides comprising an HA ectodomain of an influenza B virus HA, wherein the HA ectodomain comprises the HA stalk domain of the influenza B virus HA and the HA globular head domain of theinfluenza B virus HA with amino acid changes in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain, wherein the influenza B virus HA is influenza B virus B / Yamagata / 16 / 1988 HA, wherein: (i) the amino acid changes in the 120 loop substitute the amino acid sequence TIP and the amino acid sequence of SEQ ID NO: 1 with the amino acid sequence LIP and the amino acid sequence of SEQ ID NO: 13, respectively; (ii) the amino acid changes in the 150 loop substitute the amino acid sequence of SEQ ID NO: 2 with the amino acid sequence of SEQ ID NO: 14; (iii) the amino acid changes in the 160 loop substitute the amino acid sequence of SEQ ID NO: 3 with the amino acid sequence of SEQ ID NO: 15; and (iv) the amino acid changes in the 190 helix substitute the amino acid sequence of SEQ ID NO: 4 with the amino acid sequence of SEQ ID NO: 16. In some embodiments, the HA ectodomain further comprises 1, 2, or 3 compensatory mutations (e.g., compensatory amino acid substitutions) outside the 120 loop, 150 loop, 160 loop, and 190 helix (e.g., G252E). In some embodiments, the mosaic HA further comprises the transmembrane domain or cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises the transmembrane domain and cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises a trimerization domain (e.g., T4 fibritin (foldon) trimerization domain or GCN4- based isoleucine zipper trimerization domain).

[0146] In some embodiments, provided herein are mosaic HA polypeptides comprising an HA ectodomain of an influenza B virus HA, wherein the HA ectodomain comprises the HA stalk domain of the influenza B virus HA and the HA globular head domain of the influenza B virus HA with amino acid changes in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain, wherein the influenza B virus HA is influenza B virus B / Yamagata / 16 / 1988 HA, wherein: (i) the amino acid changes in the 120 loop substitute the amino acid sequence TIP and the amino acid sequence of SEQ ID NO: 1 with the amino acid sequence NIP and the amino acid sequence of SEQ ID NO: 17, respectively; (ii) the amino acid changes in the 150 loop substitute the amino acid sequence of SEQ ID NO: 2 with the amino acid sequence of SEQ ID NO: 18; (iii) the amino acid changes in the 160 loop substitute the amino acid sequence of SEQ ID NO: 3 with the amino acid sequence of SEQ ID NO: 19; and (iv) the amino acid changes in the 190 helix substitute the amino acid sequence of SEQ ID NO: 4 with the amino acid sequence of SEQ ID NO: 20. In some embodiments, the HA ectodomain further comprises 1, 2, or 3 compensatory mutations (e.g., compensatory amino acid substitutions) outside the 120 loop, 150 loop, 160 loop, and 190 helix (e.g., E156K). In some embodiments, the mosaic HA further comprises thetransmembrane domain or cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises the transmembrane domain and cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises a trimerization domain (e.g, T4 fibritin (foldon) trimerization domain or GCN4- based isoleucine zipper trimerization domain).

[0147] In some embodiments, provided herein are mosaic HA polypeptides comprising an HA ectodomain of an influenza B virus HA, wherein the HA ectodomain comprises the HA stalk domain of the influenza B virus HA and the HA globular head domain of the influenza B virus HA with amino acid changes in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain, wherein the influenza B virus HA is influenza B virus B / Brisbane / 60 / 2008 HA, wherein: (i) the amino acid changes in the 120 loop substitute the amino acid sequence KIP and the amino acid sequence of SEQ ID NO: 21 with the amino acid sequence NIP and the amino acid sequence of SEQ ID NO: 25, respectively; (ii) the amino acid changes in the 150 loop substitute the amino acid sequence of SEQ ID NO: 22 with the amino acid sequence of SEQ ID NO: 26; (iii) the amino acid changes in the 160 loop substitute the amino acid sequence of SEQ ID NO: 23 with the amino acid sequence of SEQ ID NO: 27; and (iv) the amino acid changes in the 190 helix substitute the amino acid sequence of SEQ ID NO: 24 with the amino acid sequence of SEQ ID NO: 28 or 37. In some embodiments, the HA ectodomain further comprises 1, 2, or 3 compensatory mutations (e.g., compensatory amino acid substitutions) outside the 120 loop, 150 loop, 160 loop, and 190 helix (e.g., G156K). In some embodiments, the mosaic HA further comprises the transmembrane domain or cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises the transmembrane domain and cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises a trimerization domain (e.g., T4 fibritin (foldon) trimerization domain or GCN4- based isoleucine zipper trimerization domain).

[0148] In some embodiments, provided herein are mosaic HA polypeptides comprising an HA ectodomain of an influenza B virus HA, wherein the HA ectodomain comprises the HA stalk domain of the influenza B virus HA and the HA globular head domain of the influenza B virus HA with amino acid changes in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain, wherein the influenza B virus HA is influenza B virus B / Phuket / 3073 HA, wherein: (i) the amino acid changes in the 120 loop substitute the amino acid sequence TTP and the amino acid sequence of SEQ ID NO: 29 with the amino acid sequence FTP and the amino acid sequence of SEQ ID NO: 33, respectively; (ii) the aminoacid changes in the 150 loop substitute the amino acid sequence of SEQ ID NO: 30 with the amino acid sequence of SEQ ID NO: 34; (iii) the amino acid changes in the 160 loop substitute the amino acid sequence of SEQ ID NO: 31 with the amino acid sequence of SEQ ID NO: 35; and (iv) the amino acid changes in the 190 helix substitute the amino acid sequence of SEQ ID NO: 32 with the amino acid sequence of SEQ ID NO: 36. In some embodiments, the HA ectodomain further comprises 1, 2, or 3 compensatory mutations (e.g., compensatory amino acid substitutions) outside the 120 loop, 150 loop, 160 loop, and 190 helix (e.g., G156K). In some embodiments, the mosaic HA further comprises the transmembrane domain or cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises the transmembrane domain and cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises a trimerization domain (e.g., T4 fibritin (foldon) trimerization domain or GCN4- based isoleucine zipper trimerization domain).

[0149] In some embodiments, provided herein are mosaic HA polypeptides comprising an HA ectodomain of an influenza B virus HA, wherein the HA ectodomain comprises the HA stalk domain of the influenza B virus HA and the HA globular head domain of the influenza B virus HA with amino acid changes in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain, wherein: (i) the 120 loop comprises the consensus sequences for the 120 loop in Table 2; (ii) the 150 loop comprises the consensus sequence for the 150 loop in Table 2; (iii) the 160 loop comprises the consensus sequence for the 160 loop in Table 2; and (iv) the 190 helix comprises the consensus sequence for the 190 helix in Table 2. In some embodiments, the HA ectodomain further comprises 1, 2, or 3 compensatory mutations (e.g., compensatory amino acid substitutions) outside the 120 loop, 150 loop, 160 loop, and 190 helix (e.g., 156K or 252E). In some embodiments, the mosaic HA further comprises the transmembrane domain or cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises the transmembrane domain and cytoplasmic domain of the influenza B virus HA. In some embodiments, the mosaic HA further comprises a trimerization domain (e.g., T4 fibritin (foldon) trimerization domain or GCN4-based isoleucine zipper trimerization domain).

[0150] In some embodiments, provided herein is a mosaic HA comprising the amino acid sequence of the SEQ ID NO: 38. In some embodiments, provided herein is a mosaic HA comprising an amino acid sequence that is at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to the amino acid sequence of the SEQ ID NO: 38. In some embodiments, provided herein is a mosaic HA comprising an HA ectodomainthat comprises an amino acid sequence that is at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to the amino acid sequence of the SEQ ID NO: 38. In some embodiments, provided herein is a mosaic HA comprising the amino acid sequence of the HA ectodomain of SEQ ID NO: 38.

[0151] In some embodiments, provided herein is a mosaic HA comprising the amino acid sequence of the SEQ ID NO: 40. In some embodiments, provided herein is a mosaic HA comprising an amino acid sequence that is at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to the amino acid sequence of the SEQ ID NO: 40. In some embodiments, provided herein is a mosaic HA comprising an HA ectodomain that comprises an amino acid sequence that is at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to the amino acid sequence of the SEQ ID NO: 40. In some embodiments, provided herein is a mosaic HA comprising the amino acid sequence of the HA ectodomain of SEQ ID NO: 40.

[0152] In some embodiments, provided herein is a mosaic HA comprising the amino acid sequence of the SEQ ID NO: 42. In some embodiments, provided herein is a mosaic HA comprising an amino acid sequence that is at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to the amino acid sequence of the SEQ ID NO: 42. In some embodiments, provided herein is a mosaic HA comprising an HA ectodomain that comprises an amino acid sequence that is at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to the amino acid sequence of the SEQ ID NO: 42. In some embodiments, provided herein is a mosaic HA comprising the amino acid sequence of the HA ectodomain of SEQ ID NO: 42.

[0153] In some embodiments, provided herein is a mosaic HA comprising the amino acid sequence of the SEQ ID NO: 44. In some embodiments, provided herein is a mosaic HA comprising an amino acid sequence that is at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to the amino acid sequence of the SEQ ID NO: 44. In some embodiments, provided herein is a mosaic HA comprising an HA ectodomain that comprises an amino acid sequence that is at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to the amino acid sequence of the SEQ ID NO: 44. In some embodiments, provided herein is a mosaic HA comprising the amino acid sequence of the HA ectodomain of SEQ ID NO: 44.

[0154] In some embodiments, provided herein is a mosaic HA comprising the amino acid sequence of the SEQ ID NO: 46. In some embodiments, provided herein is a mosaic HA comprising an amino acid sequence that is at least 90%, at least 95%, at least 96%, at least97%, at least 98%, or at least 99% identical to the amino acid sequence of the SEQ ID NO: 46. In some embodiments, provided herein is a mosaic HA comprising an HA ectodomain that comprises an amino acid sequence that is at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to the amino acid sequence of the SEQ ID NO: 46. In some embodiments, provided herein is a mosaic HA comprising the amino acid sequence of the HA ectodomain of SEQ ID NO: 46.

[0155] In some embodiments, provided herein is a mosaic HA comprising the amino acid sequence of the SEQ ID NO: 48. In some embodiments, provided herein is a mosaic HA comprising an amino acid sequence that is at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to the amino acid sequence of the SEQ ID NO: 48. In some embodiments, provided herein is a mosaic HA comprising an HA ectodomain that comprises an amino acid sequence that is at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to the amino acid sequence of the SEQ ID NO: 48. In some embodiments, provided herein is a mosaic HA comprising the amino acid sequence of the HA ectodomain of SEQ ID NO: 48.

[0156] In some embodiments, the mosaic HA is one described in Example 1, infra. In some embodiments, the mosaic HA is one described in Sun et al., 2019, J Virol. 93(12): e00333-19 or Liu et al., 2021, Front. Immunol., 12: 746447, each of which is incorporated by reference herein in its entirety. In some embodiments, the mosaic HA is one described in International Patent Application Publication No. WO 2017 / 218624 or U.S. Patent No.11,865,173, each of which is incorporated by reference herein in its entirety.

[0157] In some embodiments, the mosaic HA provided herein are capable of forming a three dimensional structure that is similar to the three dimensional structure of a native influenza hemagglutinin. Structural similarity might be evaluated based on any technique deemed suitable by those of skill in the art. For instance, reaction, e.g., under non-denaturing conditions, of a mosaic influenza virus hemagglutinin polypeptide with a neutralizing antibody or antiserum that recognizes a native influenza hemagglutinin might indicate structural similarity. Useful neutralizing antibodies or antisera are described in, e.g., Sui, et al., 2009, Nat. Struct. Mol. Biol. 16(3):265-273, Ekiert et al., February 26, 2009, Science [DOI: 10.1 126 / science. l 171491], and Kashyap et al., 2008, Proc. Natl. Acad. Sci. USA 105(16):5986-5991, the contents of which are hereby incorporated by reference in their entireties. In some embodiments, the antibody or antiserum is an antibody or antiserum that reacts with a non-contiguous epitope (z.e., not contiguous in primary sequence) that is formed by the tertiary or quaternary structure of a hemagglutinin.

[0158] In some embodiments, a mosaic HA described herein retains one, two, or more, or all of the functions of a wild-type influenza HA. Nonlimiting examples of functions of a wild-type influenza HA include fusogenic activity, receptor binding activity, budding, and particle formation. In a specific embodiment, a mosaic HA described herein has fusogenic activity. Assays known to one skilled in the art can be utilized the assess the fusogenic activity of a mosaic HA described herein, such as, for example, immunofluorescence assays and pseudotyped virus-like-particle assays.5.4 Nucleic Acids Encoding Mosaic HA & Methods for Producing Influenza Virus

[0159] Provided herein are nucleic acid molecules that encode a mosaic HA described herein. Due to the degeneracy of the genetic code, any nucleic acid sequence that encodes a mosaic HA described herein is encompassed herein. In some embodiments, nucleic acid sequences corresponding to naturally occurring influenza B virus HA nucleic acid sequences encoding an influenza B virus HA ectodomain are used to produce a mosaic HA. In some embodiments, nucleic acid sequences corresponding to naturally occurring influenza B virus HA nucleic acid sequences encoding an HA globular head domain, HA stem domain, HA transmembrane domain, and / or HA cytoplasmic domain are used to produce a mosaic HA. In some embodiments, the nucleic acid molecule comprises a nucleotide sequence encoding an influenza B virus HA signal peptide. In specific embodiments, a nucleic acid molecule comprises nucleotide sequences encoding a mosaic HA and preferably comprises the 5' noncoding region and 3' non-coding region from the HA of the same influenza B virus as the influenza B virus engineered to express the mosaic HA. In specific embodiments, a nucleic acid molecule comprises nucleotide sequences encoding a mosaic HA, and the 5' non-coding region, 3' non-coding region, and a nucleotide sequence encoding the signal peptide from the HA of the same influenza B virus as the influenza B virus engineered to express the mosaic HA.

[0160] In some embodiments, provided herein is a nucleic acid molecule comprising a nucleotide sequence that is at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, or at least 98% identical to the nucleotide sequence of SEQ ID NO:39. In specific embodiments, provided herein is a nucleic acid molecule comprising the nucleotide sequence of SEQ ID NO: 39. In some embodiments, provided herein is a nucleic acid molecule comprising the nucleotide sequence of SEQ ID NO:39, and cDNA sequences of the 5' noncoding region and 3' non-coding region from the HA of the same influenza B virus as the influenza B virus engineered to express the mosaic HA. In some embodiments, providedherein is a nucleic acid molecule comprising a nucleotide sequence that is at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, or at least 98% identical to the nucleotide sequence of SEQ ID NO: 41. In specific embodiments, provided herein is a nucleic acid molecule comprising the nucleotide sequence of SEQ ID NO: 41. In some embodiments, provided herein is a nucleic acid molecule comprising the nucleotide sequence of SEQ ID NO: 41, and cDNA sequences of the 5' non-coding region and 3' non-coding region from the HA of the same influenza B virus as the influenza B virus engineered to express the mosaic HA. In some embodiments, provided herein is a nucleic acid molecule comprising a nucleotide sequence that is at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, or at least 98% identical to the nucleotide sequence of SEQ ID NO: 43. In specific embodiments, provided herein is a nucleic acid molecule comprising the nucleotide sequence of SEQ ID NO: 43. In some embodiments, provided herein is a nucleic acid molecule comprising the nucleotide sequence of SEQ ID NO: 43 and cDNA sequences of the 5' noncoding region and 3' non-coding region from the HA of the same influenza B virus as the influenza B virus engineered to express the mosaic HA. In some embodiments, provided herein is a nucleic acid molecule comprising a nucleotide sequence that is at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, or at least 98% identical to the nucleotide sequence of SEQ ID NO: 47. In specific embodiments, provided herein is a nucleic acid molecule comprising the nucleotide sequence of SEQ ID NO: 47. In some embodiments, provided herein is a nucleic acid molecule comprising the nucleotide sequence of SEQ ID NO: 47, and cDNA sequences of the 5' non-coding region and 3' non-coding region from the HA of the same influenza B virus as the influenza B virus engineered to express the mosaic HA. In some embodiments, provided herein is a nucleic acid molecule comprising a nucleotide sequence that is at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, or at least 98% identical to the nucleotide sequence of SEQ ID NO: 49. In specific embodiments, provided herein is a nucleic acid molecule comprising the nucleotide sequence of SEQ ID NO: 49. In some embodiments, provided herein is a nucleic acid molecule comprising the nucleotide sequence of SEQ ID NO: 49, and cDNA sequences of the 5' noncoding region and 3' non-coding region from the HA of the same influenza B virus as the influenza B virus engineered to express the mosaic HA. In some embodiments, provided herein are negative-stranded RNA molecules of the DNA sequences provided herein.

[0161] In some embodiments, a nucleic acid molecule encoding a mosaic HA is isolated. In some embodiments, an "isolated" nucleic acid sequence refers to a nucleic acid molecule which is separated from other nucleic acid molecules which are present in the natural sourceof the nucleic acid. In other words, the isolated nucleic acid molecule can comprise heterologous nucleic acids that are not associated with it in nature. In some embodiments, an "isolated" nucleic acid molecule, such as a cDNA molecule, can be substantially free of other cellular material, or culture medium when produced by recombinant techniques, or substantially free of chemical precursors or other chemicals when chemically synthesized. The term "substantially free of cellular material" includes preparations of nucleic acids in which the nucleic acid molecule is separated from cellular components of the cells from which it is isolated or recombinantly produced. Thus, a nucleic acid molecule that is substantially free of cellular material includes preparations of a nucleic acid having less than about 30%, 20%, 10%, or 5% (by dry weight) of other nucleic acids. The term "substantially free of culture medium" includes preparations of nucleic acid in which the culture medium represents less than about 50%, 20%, 10%, or 5% of the volume of the preparation. The term "substantially free of chemical precursors or other chemicals" includes preparations in which the nucleic acid molecule is separated from chemical precursors or other chemicals which are involved in the synthesis of the nucleic acid molecule. In specific embodiments, such preparations of the nucleic acid molecule have less than about 50%, 30%, 20%, 10%, 5% (by dry weight) of chemical precursors or compounds other than the nucleic acid molecule of interest.

[0162] Provided herein are vectors, including expression vectors, containing a nucleic acid encoding a mosaic HA described herein. In a specific embodiment, the vector is an expression vector that is capable of directing the expression of a nucleic acid encoding a mosaic HA. Non-limiting examples of expression vectors include, but are not limited to, plasmids and viral vectors. In a specific embodiment, the expression vector is an influenza virus (e.g., an influenza B virus).

[0163] An expression vector comprises a nucleic acid molecule encoding a mosaic HA described herein and in a form suitable for expression of the nucleic acid molecule in a host cell. In a specific embodiment, an expression vector includes one or more regulatory sequences, selected on the basis of the host cells to be used for expression, which is operably linked to the nucleic acid molecule to be expressed. Within an expression vector, "operably linked" is intended to mean that a nucleic acid of interest is linked to the regulatory sequence(s) in a manner which allows for expression of the nucleic acid (e.g., in an in vitro transcription / translation system or in a host cell when the vector is introduced into the host cell). Regulatory sequences include promoters, enhancers and other expression control elements (e.g., polyadenylation signals). Regulatory sequences include those which directconstitutive expression of a nucleic acid molecule in many types of host cells, those which direct expression of the nucleic acid only in certain host cells (e.g., tissue-specific regulatory sequences), and those which direct the expression of the nucleic acid upon stimulation with a particular agent (e.g., inducible regulatory sequences). It will be appreciated by those skilled in the art that the design of the expression vector can depend on such factors as the choice of the host cell to be transformed, the level of expression of protein desired, etc. The term "host cell" is intended to include a particular subject cell transformed or transfected with a nucleic acid molecule and the progeny or potential progeny of such a cell. Progeny of such a cell may not be identical to the parent cell transformed or transfected with the nucleic acid molecule due to mutations or environmental influences that may occur in succeeding generations or integration of the nucleic acid sequence into the host cell genome. In specific embodiments, the host cell is a cell line.

[0164] Expression vectors can be designed for expression of a mosaic HA polypeptide described herein using prokaryotic (e.g., E. coli) or eukaryotic cells (e.g., insect cells (using baculovirus expression vectors, see, e.g., Treanor et al., 2007, JAMA, 297(14): 1577-1582 incorporated by reference herein in its entirety), yeast cells, plant cells, algae, avian, or mammalian cells). Examples of yeast host cells include, but are not limited to S. pombe and S. cerevisiae and examples, infra. An example of avian cells includes, but is not limited to EB66 cells. Examples of mammalian host cells include, but are not limited to, Crucell Per.C6 cells, Vero cells, CHO cells, VERO cells, BHK cells, HeLa cells, COS cells, MDCK cells, 293 cells, 3T3 cells or WI38 cells. In some embodiments, the hosts cells are myeloma cells, e.g., NSO cells, 45.6 TGI.7 cells, AF-2 clone 9B5 cells, AF-2 clone 9B5 cells, J558L cells, MOPC 315 cells, MPC-11 cells, NCI-H929 cells, NP cells, NSO / 1 cells, P3 NS1 Ag4 cells, P3 / NSl / l-Ag4-l cells, P3U1 cells, P3X63Ag8 cells, P3X63Ag8.653 cells, P3X63Ag8U.1 cells, RPMI 8226 cells, Sp20-Agl4 cells, U266B1 cells, X63AG8.653 cells, Y3.Ag.l.2.3 cells, and YO cells. Non-limiting examples of insect cells include 5f9, Sf21, Trichoplusia ni, Spodoptera frugiperda, and Bombyx mori. In some embodiments, a mammalian cell culture system (e.g., Chinese hamster ovary or baby hamster kidney cells) is used for expression of a mosaic HA. In some embodiments, a plant cell culture system is used for expression of a mosaic HA. See, e.g., U.S. Patent Nos. 7,504,560; 6,770,799;6,551,820; 6,136,320; 6,034,298; 5,914,935; 5,612,487; and 5,484,719, and U.S. patent application publication Nos. 2009 / 0208477, 2009 / 0082548, 2009 / 0053762, 2008 / 0038232, 2007 / 0275014 and 2006 / 0204487 for plant cells and methods for the production of proteins utilizing plant cell culture systems. In specific embodiments, plant cell culture systems arenot used for expression of a mosaic HA. The host cells comprising a nucleic acid molecule that encodes the mosaic HA described herein can be isolated, z.e., the cells are outside of the body of a subject. In some embodiments, the cells are engineered to express a mosaic HA described herein. In specific embodiments, the host cells are cells from a cell line.

[0165] In some embodiments, provided herein are host cells comprising a nucleic acid molecule comprising a nucleotide sequence encoding a mosaic HA described herein. In a specific embodiment, provided herein are host cells engineered to express a mosaic HA described herein. In a specific embodiment, provided herein are host cells comprising an expression vector comprising nucleic acid molecule encoding a mosaic HA described herein. In some embodiments, provided herein are host cells comprising an influenza virus (e.g., influenza B virus) encoding a mosaic HA and / or comprising a mosaic HA incorporated in its virion. Host cells are known to one of skill in the art and examples are provided herein. In specific embodiments, the host cells are cells from a cell line. In specific embodiments, host cells are isolated, in vitro, or in cell culture.

[0166] An expression vector can be introduced into host cells via conventional transformation, transfection, or infection techniques. Such techniques include, but are not limited to, calcium phosphate or calcium chloride co-precipitation, DEAE-dextran-mediated transfection, lipofection, and electroporation. Suitable methods for transforming or transfecting host cells can be found in Sambrook et al., 1989, Molecular Cloning - A Laboratory Manual, 2nd Edition, Cold Spring Harbor Press, New York, and other laboratory manuals. In some embodiments, a host cell is transiently transfected with an expression vector containing a nucleic acid molecule encoding a mosaic HA. In some embodiments, a host cell is stably transfected with an expression vector containing a nucleic acid molecule encoding a mosaic HA.

[0167] For stable transfection of mammalian cells, it is known that, depending upon the expression vector and transfection technique used, only a small fraction of cells may integrate the foreign DNA into their genome. In order to identify and select these integrants, a nucleic acid that encodes a selectable marker (e.g., for resistance to antibiotics) is generally introduced into the host cells along with the nucleic acid of interest. Examples of selectable markers include those which confer resistance to drugs, such as G418, hygromycin and methotrexate. Cells stably transfected with the introduced nucleic acid sequence can be identified by drug selection (e.g., cells that have incorporated the selectable marker gene will survive, while the other cells die).

[0168] As an alternative to recombinant expression of a mosaic HA using a host cell, an expression vector containing a nucleic acid encoding a mosaic HA can be transcribed and translated in vitro using, e.g., T7 promoter regulatory sequences and T7 polymerase. In a specific embodiment, a coupled transcription / translation system, such as Promega TNT®, or a cell lysate or cell extract comprising the components necessary for transcription and translation may be used to produce a mosaic HA.

[0169] Once a mosaic HA has been produced, it may be isolated or purified by any method known in the art for isolation or purification of a protein, for example, by chromatography (e.g., ion exchange, affinity, particularly by affinity for the specific antigen, by Protein A, and sizing column chromatography), centrifugation, differential solubility, or by any other standard technique for the isolation or purification of proteins.

[0170] Accordingly, provided herein are methods for producing a mosaic HA. In some embodiments, the method comprises culturing a host cell containing a nucleic acid molecule encoding a mosaic HA in a suitable medium such that the mosaic B is produced. In a specific embodiment, the method comprises culturing a host cell containing a nucleic acid molecule comprising a nucleotide sequence encoding a mosaic HA, or a host cell containing an expression vector containing a nucleic acid molecule comprising a nucleotide sequence encoding a mosaic HA in a suitable medium such that the mosaic HA is produced. In some embodiments, the method further comprises isolating the mosaic HA from the medium or the host cell.

[0171] Also provided herein are methods for producing an influenza virus (e.g., an influenza B virus) comprising a mosaic HA described herein, comprising propagating the virus in any substrate that allows the virus to grow to titers that permit their use in accordance with the methods described herein. In some embodiments, the substrate allows the virus to grow to titers comparable to those determined for the corresponding wild-type virus. In some embodiments, the virus is propagated in embryonated eggs (e.g., chicken eggs). In a specific embodiment, the virus is propagated in 8 day old, 9-day old, 8-10 day old, 10 day old, 11-day old, 10-12 day old, or 12-day old embryonated eggs (e.g., chicken eggs). In some embodiments, the virus is propagated in MDCK cells, Vero cells, 293T cells, or other cell lines known in the art. In some embodiments, the virus is propagated in cells derived from embryonated eggs.

[0172] In one aspect, provided herein are influenza viruses (e.g., influenza B viruses) containing a mosaic HA described herein. In a specific embodiment, the mosaic HA is incorporated into the virions of the influenza virus. In some embodiments, the influenza Bvirus is one disclosed herein (e.g., in Section 6, infra). In some embodiments, the influenza B virus is of the B / Victoria lineage. In some embodiments, the influenza B virus is of the B / Yamagata lineage. In some embodiments, the influenza B virus is one disclosed in FIG. IG or 1H

[0173] Influenza viruses (e.g., influenza B viruses) containing a mosaic HA may be produced by supplying in trans the mosaic HA during production of virions using techniques known to one skilled in the art, such as reverse genetics and helper-free plasmid rescue. Alternatively, the replication of an influenza virus comprising a genome engineered to express a mosaic HA in cells susceptible to infection with the virus, wherein hemagglutinin function is provided in trans will produce progeny influenza viruses containing the mosaic HA.

[0174] In another aspect, provided herein are influenza viruses (e.g., influenza B viruses) comprising a genome engineered to express a mosaic HA. In a specific embodiment, the genome of a parental influenza virus (e.g., influenza B virus) is engineered to encode a mosaic HA, which is expressed by progeny influenza virus. In specific embodiments, the genome of a parental influenza virus (e.g., influenza B virus) is engineered to encode a mosaic HA, which is expressed and incorporated into the virions of progeny influenza virus. Thus, the progeny influenza virus resulting from the replication of the parental influenza virus contain a mosaic HA. The virions of the parental influenza virus (e.g., influenza B virus) may have incorporated into them a mosaic HA that contains an HA ectodomain and / or transmembrane and cytoplasmic domains from the same or a different group, lineage, or strain of influenza virus (e.g., influenza B viruses).

[0175] In some embodiments, the genome of the influenza virus (e.g., influenza B virus) comprises genes encoding non- structural proteins and matrix protein of influenza B virus. In some embodiments, the genome of the influenza virus (e.g., influenza B virus) comprises a gene encoding influenza B virus neuraminidase, wherein the strain of the influenza B virus neuraminidase is the same influenza B virus strain as the strain of the HA globular head domain, HA stem domain, HA transmembrane domain, and / or cytoplasmic domain of the mosaic HA. In some embodiments, the genome of the influenza virus (e.g., influenza B virus) comprises a gene encoding influenza B virus neuraminidase, wherein the strain of the influenza B virus neuraminidase is the same influenza B virus strain as the strain of the HA ectodomain of the mosaic HA.

[0176] In some embodiments, the virions of the parental influenza virus (e.g., influenza B virus) have incorporated into them an influenza virus (e.g., influenza B virus) neuraminidase,wherein the strain of the influenza B virus neuraminidase is not the same strain as the strain of the HA globular head domain or HA stem domain of the mosaic HA. In some embodiments, the influenza B virus neuraminidase corresponds to the influenza B virus neuraminidase of the HA stem domain of the mosaic HA. In some embodiments, the influenza B virus neuraminidase corresponds to the influenza B virus neuraminidase of the HA globular head domain of the mosaic HA.

[0177] Since the genome of influenza B virus consists of eight (8) single-stranded, negative sense segments, the genome of a parental influenza virus may be engineered to express a mosaic HA using a recombinant segment and techniques known to one skilled in the art, such a reverse genetics and helper-free plasmid rescue. In some embodiment, the recombinant segment comprises a nucleic acid encoding the mosaic HA as well as the 3' and 5' incorporation signals which are required for proper replication, transcription and packaging of the vRNAs (Fujii et al., 2003, Proc. Natl. Acad. Sci. USA 100:2002-2007; Zheng, et al., 1996, Virology 217:242-251, International Publication No. WO 2011 / 014645, all of which are incorporated by reference herein in their entireties). In a specific embodiment, the recombinant segment uses the 3' and 5' noncoding and / or non-translated sequences of segments of influenza viruses that are from a different or the same group, lineage, or strain as the parental influenza virus (e.g., influenza B virus). In some embodiments, the recombinant segment comprises the 3' noncoding region of an influenza B virus HA, the untranslated regions of an influenza B virus HA, and the 5' non-coding region of an influenza B virus HA. In specific embodiments, the recombinant segment comprises the 3' and 5' noncoding and / or non-translated sequences of the HA segment of an influenza B virus that is the same group, lineage, or strain as the influenza B virus group, lineage, or strain as the HA stem domain of a mosaic HA. In some embodiments, the recombinant segment comprises the 3' and 5' noncoding and / or non-translated sequences of the HA segment of an influenza B virus that is the same group, lineage, or strain as the influenza B virus group, lineage, or strain as the HA globular head domain of a mosaic HA. In specific embodiments, the recombinant segment comprises packaging signals, such as the 5' and 3' non-coding regions and signal peptide of the HA segment of an influenza B virus, from the same group, lineage, or strain as the influenza B virus backbone. For example, if the mosaic HA is engineered to be expressed from an influenza B virus, then the nucleotide sequence encoding mosaic HA comprises the 5' and 3' non-coding regions and the nucleotide sequence encoding the signal peptide of the HA segment of the influenza B virus. In specific embodiments, the recombinant segment encoding the mosaic HA replaces the HA segment of a parental influenza B virus.

[0178] In some embodiments, a chimeric hemagglutinin gene segment encodes a mosaic HA. In specific embodiments, the chimeric hemagglutinin gene segment and at least one other influenza virus gene segment comprise packaging signals that enable the chimeric hemagglutinin gene segment and the at least one other gene segment to segregate together during replication of a recombinant influenza virus (see, Gao & Palese 2009, PNAS 106: 15891-15896; U.S. Patent No. 8,828,406; and International Application Publication No. WO 11 / 014645).

[0179] In some embodiments, the genome of a parental influenza virus (e.g., influenza B virus) may be engineered to express a mosaic HA using a recombinant segment that is bicistronic. Bicistronic techniques allow the engineering of coding sequences of multiple proteins into a single mRNA through the use of internal ribosome entry site (IRES) sequences. IRES sequences direct the internal recruitment of ribosomes to the RNA molecule and allow downstream translation in a cap independent manner. Briefly, a coding region of one protein is inserted into the open reading frame (ORF) of a second protein. The insertion is flanked by an IRES and any untranslated signal sequences necessary for proper expression and / or function. The insertion must not disrupt the ORF, polyadenylation or transcriptional promoters of the second protein (see, e.g., Garcia-Sastre et al., 1994, J. Virol. 68:6254-6261 and Garcia-Sastre et al., 1994 Dev. Biol. Stand. 82:237-246, each of which is hereby incorporated by reference in its entirety). See also, e.g., U.S. Patent No. 6,887,699, U.S. Patent No. 6,001,634, U.S. Patent No. 5,854,037 and U.S. Patent No. 5,820,871, each of which is incorporated herein by reference in its entirety. Any IRES known in the art or described herein may be used in accordance with the invention (e.g., the IRES of BiP gene, nucleotides 372 to 592 of GenBank database entry HUMGRP78; or the IRES of encephalomyocarditis virus (EMCV), nucleotides 1430-2115 of GenBank database entry CQ867238.). Thus, in some embodiments, a parental influenza virus (e.g., influenza B virus) is engineered to contain a bicistronic RNA segment that expresses the mosaic HA and another polypeptide, such as a gene expressed by the parental influenza virus. In some embodiments, the parental influenza virus gene is the HA gene.

[0180] Techniques known to one skilled in the art may be used to produce an influenza virus (e.g., influenza B virus) containing a mosaic HA and an influenza virus (e.g., influenza B virus) comprising a genome engineered to express a mosaic HA. For example, reverse genetics techniques may be used to generate such an influenza virus (e.g., influenza B virus). Briefly, reverse genetics techniques generally involve the preparation of synthetic recombinant viral RNAs that contain the non-coding regions of the negative- strand, viralRNA which are essential for the recognition by viral polymerases and for packaging signals necessary to generate a mature virion. The recombinant RNAs are synthesized from a recombinant DNA template and reconstituted in vitro with purified viral polymerase complex to form recombinant ribonucleoproteins (RNPs) which can be used to transfect cells. A more efficient transfection is achieved if the viral polymerase proteins are present during transcription of the synthetic RNAs either in vitro or in vivo. The synthetic recombinant RNPs can be rescued into infectious virus particles. The foregoing techniques are described in U.S. Patent No. 5,166,057 issued November 24, 1992; in U.S. Patent No. 5,854,037 issued December 29, 1998; in European Patent Publication EP 0702085A1, published February 20, 1996; in U.S. Patent Application Serial No. 09 / 152,845; in International Patent Application Publication No. WO 97 / 12032 published April 3, 1997; Application Publication No. WO 96 / 34625 published November 7, 1996; in European Patent Publication No. EP A780475; WO 99 / 02657 published January 21, 1999; Application Publication No. WO 98 / 53078 published November 26, 1998; Application Publication No. WO 98 / 02530 published January 22, 1998; Application Publication No. WO 99 / 15672 published April 1, 1999; Application Publication No. WO 98 / 13501 published April 2, 1998; Application Publication No. WO 97 / 06270 published February 20, 1997; and European Patent Application Publication No. 780 475 Al published June 25, 1997, each of which is incorporated by reference herein in its entirety.

[0181] Alternatively, helper-free plasmid technology may be used to produce an influenza virus (e.g., influenza B virus) containing a mosaic HA and an influenza virus (e.g., influenza B virus) comprising a genome engineered to express a mosaic HA. Briefly, full length cDNAs of viral segments are amplified using PCR with primers that include unique restriction sites, which allow the insertion of the PCR product into the plasmid vector (Flandorfer et al., 2003, J. Virol. 77:9116-9123; Nakaya et al., 2001, J. Virol. 75: 11868- 11873; both of which are incorporated herein by reference in their entireties). The plasmid vector is designed so that an exact negative (vRNA sense) transcript is expressed. For example, the plasmid vector may be designed to position the PCR product between a truncated human RNA polymerase I promoter and a hepatitis delta virus ribozyme sequence such that an exact negative (vRNA sense) transcript is produced from the polymerase I promoter. Separate plasmid vectors comprising each viral segment as well as expression vectors comprising necessary viral proteins may be transfected into cells leading to production of recombinant viral particles. In another example, plasmid vectors from which both the viral genomic RNA and mRNA encoding the necessary viral proteins are expressedmay be used. For a detailed description of helper-free plasmid technology see, e.g., International Patent Application Publication No. WO 01 / 04333; U.S. Patent Nos. 6,951,754, 7,384,774, 6,649,372, and 7,312,064; Fodor et al., 1999, J. Virol. 73:9679-9682; Quinlivan et al., 2005, J. Virol. 79:8431-8439; Hoffmann et al., 2000, Proc. Natl. Acad. Sci. USA 97:6108-6113; and Neumann et al., 1999, Proc. Natl. Acad. Sci. USA 96:9345-9350, each of which is incorporated herein by reference in its entirety.

[0182] The influenza viruses (e.g., influenza B viruses) described herein may be propagated in any substrate that allows the virus to grow to titers that permit their use in accordance with the methods described herein. Thus, in some embodiments, provided herein is a method for producing an influenza virus (e.g., influenza B virus) described herein comprising propagating the virus in a substrate. In some embodiments, the substrate allows the viruses to grow to titers comparable to those determined for the corresponding wild-type viruses. In some embodiments, the substrate is one which is biologically relevant to the influenza virus (e.g., influenza B virus) or to the virus from which the HA function is derived. In a specific embodiment, an attenuated influenza virus (e.g., influenza B virus) by virtue of, e.g., a mutation in the NS1 gene, may be propagated in an IFN-deficient substrate. For example, a suitable IFN-deficient substrate may be one that is defective in its ability to produce or respond to interferon, or is one which an IFN-deficient substrate may be used for the growth of any number of viruses which may require interferon-deficient growth environment. See, for example, U.S. Patent Nos. 6,573,079, issued June 3, 2003, 6,852,522, issued February 8, 2005, and 7,494,808, issued February 24, 2009, the entire contents of each of which is incorporated herein by reference in its entirety. In some embodiments, the virus is propagated in embryonated eggs (e.g., chicken eggs). In a specific embodiment, the virus is propagated in 8 day old, 9-day old, 8-10 day old, 10 day old, 11-day old, 10-12 day old, or 12-day old embryonated eggs (e.g., chicken eggs). In some embodiments, the virus is propagated in a cell line susceptible to influenza virus infection. In some embodiments, the virus is propagated in MDCK cells, Vero cells, 293T cells, or other cell lines known in the art. In some embodiments, the virus is propagated in cells derived from embryonated eggs.

[0183] The influenza viruses (e.g., influenza B viruses) described herein may be isolated and purified by any method known to those of skill in the art. In some embodiments, the virus is removed from cell culture and separated from cellular components, typically by well- known clarification procedures, e.g., such as gradient centrifugation and column chromatography, and may be further purified as desired using procedures well known to those skilled in the art, e.g., plaque assays.

[0184] In specific embodiments, the influenza viruses, or influenza virus polypeptides, genes or genome segments for use as described herein are obtained or derived from an influenza B virus. In specific embodiments, the influenza viruses, or influenza virus polypeptides, genes or genome segments for use as described herein are obtained or derived from a single influenza B virus. In some embodiments, the influenza viruses, or influenza virus polypeptides, genes or genome segments for use as described herein are obtained or derived from two or more influenza B virus lineages or strains. In some embodiments, the influenza B virus is an influenza B virus of the Yamagata lineage. In some embodiments, the influenza B virus is an influenza B virus of the Victoria lineage. In some embodiments, the influenza B virus is one disclosed herein (e.g., in Section 5.4 or Example 1). In some embodiments, the influenza B virus is one disclosed in FIG. 1G or 1H. In a specific embodiment, the influenza B virus is an influenza B / Yamagata / 16 / 1988 virus. In a specific embodiment, the influenza B virus is an influenza B / Phuket / 3073 / 2013 virus. In a specific embodiment, the influenza B virus is an influenza B / Brisbane / 60 / 2008 virus.

[0185] Non-limiting examples of influenza B viruses include strain Aichi / 5 / 88, strain B / Brisbane / 60 / 2008; Akita / 27 / 2001, strain Akita / 5 / 2001, strain Alaska / 16 / 2000, strain Alaska / 1777 / 2005, strain Argentina / 69 / 2001, strain Arizona / 146 / 2005, strain Arizona / 148 / 2005, strain Bangkok / 163 / 90, strain Bangkok / 34 / 99, strain Bangkok / 460 / 03, strain Bangkok / 54 / 99, strain Barcelona / 215 / 03, strain Beijing / 15 / 84, strain Beijing / 184 / 93, strain Beijing / 243 / 97, strain Beijing / 43 / 75, strain Beijing / 5 / 76, strain Beijing / 76 / 98, strain Belgium / WVl 06 / 2002, strain Belgium / WVl 07 / 2002, strain Bel gium / WVl 09 / 2002, strain Belgium / WVl 14 / 2002, strain Belgium / WVl 22 / 2002, strain Bonn / 43, strain Brazil / 952 / 2001, strain Bucharest / 795 / 03, strain Buenos Aires / 161 / 00), strain Buenos Aires / 9 / 95, strain Buenos Aires / SW 16 / 97, strain Buenos Aires / VL518 / 99, strain Canada / 464 / 2001, strain Canada / 464 / 2002, strain Chaco / 366 / 00, strain Chaco / Rl 13 / 00, strain Cheju / 303 / 03, strain Chiba / 447 / 98, strain Chongqing / 3 / 2000, strain clinical isolate SAI Thailand / 2002, strain clinical isolate SA10 Thailand / 2002, strain clinical isolate SA100 Philippines / 2002, strain clinical isolate SA101 Philippines / 2002, strain clinical isolate SAHO Philippines / 2002), strain clinical isolate SAI 12 Philippines / 2002, strain clinical isolate SAI 13 Philippines / 2002, strain clinical isolate SAI 14 Philippines / 2002, strain clinical isolate SA2 Thailand / 2002, strain clinical isolate SA20 Thailand / 2002, strain clinical isolate SA38 Philippines / 2002, strain clinical isolate SA39 Thailand / 2002, strain clinical isolate SA99 Philippines / 2002, strain CNIC / 27 / 2001, strain Colorado / 2597 / 2004, strain Cordoba / VA418 / 99, strainCzechoslovakia / 16 / 89, strain Czechoslovakia / 69 / 90, strain Daeku / 10 / 97, strain Daeku / 45 / 97,strain Daeku / 47 / 97, strain Daeku / 9 / 97, strain B / Du / 4 / 78, strain B / Durban / 39 / 98, strain Durban / 43 / 98, strain Durban / 44 / 98, strain B / Durban / 52 / 98, strain Durban / 55 / 98, strain Durban / 56 / 98, strain England / 1716 / 2005, strain England / 2054 / 2005) , strain England / 23 / 04, strain Finland / 154 / 2002, strain Finland / 159 / 2002, strain Finland / 160 / 2002, strain Finland / 161 / 2002, strain Finland / 162 / 03, strain Finland / 162 / 2002, strain Finland / 162 / 91, strain Finland / 164 / 2003, strain Finland / 172 / 91, strain Finland / 173 / 2003, strain Finland / 176 / 2003, strain Finland / 184 / 91, strain Finland / 188 / 2003, strain Finland / 190 / 2003, strain Finland / 220 / 2003, strain Finland / WV5 / 2002, strain Fujian / 36 / 82, strain Geneva / 5079 / 03, strain Genoa / 11 / 02, strain Genoa / 2 / 02, strain Genoa / 21 / 02, strain Genova / 54 / 02, strain Genova / 55 / 02, strain Guangdong / 05 / 94, strain Guangdong / 08 / 93, strain Guangdong / 5 / 94, strain Guangdong / 55 / 89, strain Guangdong / 8 / 93, strain Guangzhou / 7 / 97, strain Guangzhou / 86 / 92, strain Guangzhou / 87 / 92, strain Gyeonggi / 592 / 2005, strain Hannover / 2 / 90, strain Harbin / 07 / 94, strain Hawaii / 10 / 2001, strain Hawaii / 1990 / 2004, strain Hawaii / 38 / 2001, strain Hawaii / 9 / 2001, strain Hebei / 19 / 94, strain Hebei / 3 / 94) , strain Henan / 22 / 97, strain Hiroshima / 23 / 2001, strain Hong Kong / 110 / 99, strain Hong Kong / 1115 / 2002, strain Hong Kong / 112 / 2001, strain Hong Kong / 123 / 2001, strain Hong Kong / 1351 / 2002, strain Hong Kong / 1434 / 2002, strain Hong Kong / 147 / 99, strain Hong Kong / 156 / 99, strain Hong Kong / 157 / 99, strain Hong Kong / 22 / 2001, strain Hong Kong / 22 / 89, strain Hong Kong / 336 / 2001, strain Hong Kong / 666 / 2001, strain Hong Kong / 9 / 89, strain Houston / 1 / 91, strain Houston / 1 / 96, strain Houston / 2 / 96, strain Hunan / 4 / 72, strain Ibaraki / 2 / 85, strain ncheon / 297 / 2005, strain India / 3 / 89, strain India / 77276 / 2001, strain Israel / 95 / 03, strain Israel / WVl 87 / 2002, strain Japan / 1224 / 2005, strain Jiangsu / 10 / 03, strain Johannesburg / 1 / 99, strain Johannesburg / 96 / 01, strain Kadoma / 1076 / 99, strainKadoma / 122 / 99, strain Kagoshima / 15 / 94, strain Kansas / 22992 / 99, strain Khazkov / 224 / 91, strain Kobe / 1 / 2002, strain, strain Kouchi / 193 / 99, strain Lazio / 1 / 02, strain Lee / 40, strain Leningrad / 129 / 91, strain Lissabon / 2 / 90) , strain Los Angeles / 1 / 02, strain Lusaka / 270 / 99, strain Lyon / 1271 / 96, strain Malaysia / 83077 / 2001, strain Maputo / 1 / 99, strain Mar del Plata / 595 / 99, strain Maryland / 1 / 01, strain Memphis / 1 / 01, strain Memphis / 12 / 97-MA, strain Michigan / 22572 / 99, strain Mie / 1 / 93, strain Milano / 1 / 01, strain Minsk / 318 / 90, strain Moscow / 3 / 03, strain Nagoya / 20 / 99, strain Nanchang / 1 / 00, strain Nashville / 107 / 93, strain Nashville / 45 / 91, strain Nebraska / 2 / 01, strain Netherland / 801 / 90, strain Netherlands / 429 / 98, strain New York / 1 / 2002, strain NIB / 48 / 90, strain Ningxia / 45 / 83, strain Norway / 1 / 84, strain Oman / 16299 / 2001, strain Osaka / 1059 / 97, strain Osaka / 983 / 97-V2, strain Oslo / 1329 / 2002, strain Oslo / 1846 / 2002, strain Panama / 45 / 90, strain Paris / 329 / 90, strain Parma / 23 / 02, strainPerth / 211 / 2001, strain Peru / 1364 / 2004, strain Philippines / 5072 / 2001, strain Pusan / 270 / 99, strain Quebec / 173 / 98, strain Quebec / 465 / 98, strain Quebec / 7 / 01, strain Roma / 1 / 03, strain Saga / S172 / 99, strain Seoul / 13 / 95, strain Seoul / 37 / 91, strain Shangdong / 7 / 97, strain Shanghai / 361 / 2002) , strain Shiga / T30 / 98, strain Sichuan / 379 / 99, strain Singapore / 222 / 79, strain Spain / WV27 / 2002, strain Stockholm / 10 / 90, strain Switzerland / 5441 / 90, strain Taiwan / 0409 / 00, strain Taiwan / 0722 / 02, strain Taiwan / 97271 / 2001, strain Tehran / 80 / 02, strain Tokyo / 6 / 98, strain Trieste / 28 / 02, strain Ulan Ude / 4 / 02, strain United Kingdom / 34304 / 99, strain USSR / 100 / 83, strain Victoria / 103 / 89, strain Vienna / 1 / 99, strain Wuhan / 356 / 2000, strain WV194 / 2002, strain Xuanwu / 23 / 82, strain Yamagata / 1311 / 2003, strain Yamagata / K500 / 2001, strain Alaska / 12 / 96, strain GA / 86, strain NAGASAKI / 1 / 87, strain Tokyo / 942 / 96, strain B / Wisconsin / 1 / 2010; and strain Rochester / 02 / 2001.

[0186] Other examples of influenza B viruses may be found elsewhere in the application, such as in, e.g., Section 5.3 above and Section 6 below.

[0187] In some embodiments, the influenza viruses (e.g., influenza B viruses) provided herein have an attenuated phenotype. In specific embodiments, the attenuated influenza virus is based on influenza B virus. In some embodiments, the attenuated influenza virus may comprise genes or genome segments from one or more strains or lineages of influenza B virus. In specific embodiments, the attenuated influenza B virus comprises, encodes, or both, a mosaic HA and has a backbone of an influenza B virus.

[0188] In specific embodiments, attenuation of influenza virus (e.g., influenza B viruses) is desired such that the virus remains, at least partially, infectious and can replicate in vivo, but only generate low titers resulting in subclinical levels of infection that are non- pathogenic. Such attenuated viruses are especially suited for embodiments described herein wherein the virus or an immunogenic composition thereof is administered to a subject to induce an immune response. Attenuation of the influenza virus (e.g., influenza B viruses) can be accomplished according to any method known in the art, such as, e.g., selecting viral mutants generated by chemical mutagenesis, mutation of the genome by genetic engineering, selecting reassortant viruses that contain segments with attenuated function (e.g., truncated NS1 protein (see, e.g., Hai et al., 2008, Journal of Virology 82(21): 10580-10590, which is incorporated by reference herein in its entirety) or NS1 deletion (see, e.g., Wressnigg et al, 2009, Vaccine 27:2851-2857, which is incorporated by reference herein in its entirety)), or selecting for conditional virus mutants (e.g., cold-adapted viruses, see, e.g., Alexandrova et al., 1990, Vaccine, 8:61-64, which is incorporated by reference herein in its entirety).Alternatively, naturally occurring attenuated influenza viruses (e.g. , naturally occurringattenuated influenza B viruses) may be used as influenza virus (e.g., influenza B virus) backbones for the influenza virus vectors (e.g., influenza B virus vectors).

[0189] In some embodiments, an influenza virus (e.g., influenza B virus) that contains a mosaic HA is propagated in embryonated chicken eggs. In some embodiments, an influenza virus (e.g., influenza B virus) that contains a mosaic HA is not propagated in embryonated chicken eggs. In some embodiments, an influenza virus (e.g., influenza B virus) that contains a mosaic HA is propagated in embryonated chicken egg cells. In some embodiments, an influenza virus (e.g., influenza B virus) that contains a mosaic HA polypeptide is propagated in mammalian cells, e.g., immortalized human cells (see, e.g., International Application No. PCT / EP2006 / 067566 published as International Publication No. WO 07 / 045674 which is herein incorporated by reference in its entirety) or canine kidney cells such as MDCK cells (see, e.g., International Application No. PCT / IB2007 / 003536 published as International Publication No. WO 08 / 032219 which is herein incorporated by reference in its entirety). In some embodiments, an influenza B virus containing a mosaic HA is produced as described in Example 1 (see, e.g., FIG. IE).

[0190] In some embodiments, an influenza virus (e.g., influenza B virus) comprising a mosaic HA described herein has one, two, or more of the functions of an influenza virus (e.g., influenza B virus) comprising a wild-type influenza virus HA (e.g., wild-type influenza B virus HA). Non-limiting examples of functions of a wild-type influenza virus HA (e.g., wildtype influenza B virus HA) include fusogenic activity, receptor binding activity, budding, and particle formation. In a specific embodiment, an influenza B virus comprising a mosaic HA polypeptide described herein has fusogenic activity. Assays known to one skilled in the art can be utilized to assess the fusogenic activity of an influenza virus comprising a mosaic HA polypeptide described herein, such as, for example, immunofluorescence assays and pseudotyped virus-like-particle assays. In a specific embodiment, an influenza B virus comprising a mosaic HA described herein has replication activity. Assays known to one skilled in the art can be utilized the assess the replication activity of influenza B virus comprising a mosaic HA described herein, such as, for example, plaque assay and western blot analyses.

[0191] In some embodiments, an influenza virus (e.g., an influenza B virus) containing a mosaic HA is inactivated. Techniques known to one of skill in the art may be used to inactivate viruses containing a mosaic HA. Common methods use formalin, heat, or detergent for inactivation. See, e.g., U.S. Patent No. 6,635,246, which is herein incorporated by reference in its entirety. Other methods include those described in U.S. Patent Nos.5,891,705; 5,106,619, 4,693,981, 7,238,349, and 7,316,813, U.S. Patent Application Publication Nos. 2008 / 0181911 and 2009 / 0263422, and International Patent Application Publication Nos. WO 2001 / 022992, WO 2006 / 100109, WO 2002 / 097072, and WO 2008 / 009309, each which are incorporated herein by reference in their entireties. In some embodiments, an influenza B virus is inactivated using formaldehyde or beta-propiolactone. In some embodiments, the inactivated influenza B virus is purified by ultracentrifugation. In specific embodiments, an inactivated influenza B virus is produced using methods described in Section 6, infra.

[0192] In some embodiments, inactivated influenza virus (e.g, inactivated influenza B virus) that contains a mosaic HA was propagated in embryonated chicken eggs before its inactivation and subsequent use in an immunogenic composition described herein. In some embodiments, the inactivated influenza virus (e.g, inactivated influenza B virus) that contains a mosaic HA was not propagated in embryonated chicken eggs before its inactivation and subsequent use in an immunogenic composition described herein. In some embodiments, the inactivated influenza virus (e.g., inactivated influenza B virus) that contains a mosaic HA was propagated in embryonated chicken egg cells before its inactivation and subsequent use in an immunogenic composition described herein. In some embodiments, the inactivated influenza virus (e.g., inactivated influenza B virus) that contains a mosaic HA polypeptide was propagated in mammalian cells, e.g., immortalized human cells (see, e.g., International Application No. PCT / EP2006 / 067566 published as International Publication No. WO 07 / 045674 which is herein incorporated by reference in its entirety) or canine kidney cells such as MDCK cells (see, e.g., International Application No. PCT / IB2007 / 003536 published as International Publication No. WO 08 / 032219 which is herein incorporated by reference in its entirety) before its inactivation and subsequent use in an immunogenic composition described herein.

[0193] In some embodiments, an influenza virus (e.g., an influenza B virus) containing a mosaic HA is inactivated and split. Techniques for producing split virus vaccines are known to those skilled in the art. By way of non-limiting example, an influenza virus split vaccine may be prepared using inactivated particles disrupted with detergents. One example of a split virus vaccine that can be adapted for use in accordance with the methods described herein is the fluzone®, Influenza Virus Vaccine (Zonal Purified, Subvirion) for intramuscular use, which is formulated as a sterile suspension prepared from influenza viruses propagated in embryonated chicken eggs. The virus-containing fluids are harvested and inactivated with formaldehyde or beta-propiolactone. Influenza virus is concentrated and purified in a linearsucrose density gradient solution using a continuous flow centrifuge. The virus is then chemically disrupted using a nonionic surfactant, octoxinol-9, (Triton® X- 100 - A registered trademark of Union Carbide, Co.) producing a "split virus." The split virus is then further purified by chemical means and suspended in sodium phosphate-buffered isotonic sodium chloride solution. In some embodiments, an influenza B virus is inactivated using formaldehyde or beta-propiolactone, the inactivated influenza B virus is purified by ultracentrifugation, and the purified inactivated influenza B virus is treated with Triton X-100 to prepare an inactivated split influenza B virus. In specific embodiments, an inactivated split influenza B virus is produced using methods described in Section 6, infra.

[0194] In some embodiments, the inactivated split influenza B virus is prepared using influenza virus that was propagated in embryonated chicken eggs. In some embodiments, the inactivated split influenza B virus is prepared using influenza virus that was not propagated in embryonated chicken eggs. In some embodiments, the inactivated split influenza B virus is prepared using influenza virus that was propagated in embryonated chicken egg cells. In some embodiments, the inactivated split influenza B virus is prepared using influenza B virus that was propagated in mammalian cells, e.g., immortalized human cells (see, e.g., PCT / EP2006 / 067566 published as WO 07 / 045674 which is herein incorporated by reference in its entirety) or canine kidney cells such as MDCK cells (see, e.g., PCT / IB2007 / 003536 published as WO 08 / 032219 which is herein incorporated by reference in its entirety). Other methods for preparing the split virus vaccine are known in the art, such as, e.g. , those described in U.S. Patent Nos. 7,238,349 and 7,316,813, U.S. Patent Application Publication Nos. 2008 / 0181911 and 2009 / 0263422, and International Patent Application Publication Nos. WO 2001 / 022992, WO 2006 / 100109, WO 2002 / 097072, and WO 2008 / 009309, each which are incorporated herein by reference in their entireties.5.5 Prophylactic Uses

[0195] In one aspect, provided herein are methods of preventing influenza virus disease (e.g., influenza virus disease caused by influenza B virus) in a subject, methods of immunizing a subject against influenza virus disease (e.g., influenza virus disease caused by influenza B virus), and methods of inducing an immune response to influenza B viruses (e.g. , a cross-reactive immune response to plurality of influenza B virus strains or lineages) using an immunogenic composition described herein. In some embodiments, provided herein are methods of inducing a cross-reactive immune response to plurality of influenza B virus strains or lineages using an immunogenic composition described herein.

[0196] In some embodiments, provided herein is a method of preventing influenza virus disease (e.g., influenza virus disease caused by an influenza B virus) in a subject, comprising administering to the subject an immunogenic composition described herein. In some embodiments, provided herein is a method of immunizing a subject against influenza virus disease (e.g., influenza virus disease caused by influenza B virus), comprising administering to the subject an immunogenic composition described herein. In some embodiments, provided herein is a method of inducing immune response to influenza B viruses in a subject, comprising administering to the subject an immunogenic composition described herein. In some embodiments, provided herein is a method of inducing a cross-reactive immune response to two or more influenza B viruses in a subject, comprising administering to the subject an immunogenic composition described herein. In some embodiments, the immunogenic composition is administered intramuscularly to the subject. In some embodiments, the immunogenic composition is administered intranasally to the subject. In some embodiments, the inactivated influenza B virus or inactivated split influenza B virus in an immunogenic composition is administered to the subject at a dose provided herein. In some embodiments, the CpG oligonucleotide adjuvant in an immunogenic composition is administered to the subject at a dose provided herein. In some embodiments, the methods include the administration of more than one immunogenic composition described herein to a subject (e.g., a human). For example, a first immunogenic composition described herein may be administered to a subject (e.g., a human) to prime the immune response and one, two, or more boosters of immunogenic compositions described herein may be administered to the subject. In some embodiments, the mosaic HA in each immunogenic composition is different.

[0197] While not intending to be bound by any particular theory of operation, it is believed that sequential immunization with mosaic HAs that express the same HA stem domain and distinct HA globular head domains are useful for presenting one or more relatively conserved antigenic regions to a subject’s immune system in order to generate an immune response that is capable of cross-reacting with a plurality of influenza B virus strains and lineages. Accordingly, in some embodiments, provided herein are methods of inducing an immune response in a subject (e.g., human subject) that is capable of cross-reacting with a plurality of influenza B virus strains and lineages, comprising sequentially administering to the subject two or more immunogenic compositions described herein, wherein each immunogenic composition comprises a mosaic HA and a CpG oligonucleotide adjuvant described herein, wherein each mosaic HA is different from each other. In someembodiments, provided herein are methods of inducing an immune response in a subject (e.g., human subject) that is capable of cross-reacting with a plurality of influenza B virus strains and lineages, comprising sequentially administering to the subject two or more immunogenic compositions described herein, wherein one or more (e.g., two or more) of the immunogenic compositions comprises an inactivated or an inactivated split influenza B virus and a CpG oligonucleotide adjuvant described herein, wherein each inactivated or inactivated split influenza B virus comprises a mosaic HA, and wherein each mosaic HA is different from each other. In some embodiments, provided herein are methods of inducing an immune response in a subject (e.g., human subject) that is capable of cross-reacting with a plurality of influenza B virus strains and lineages, comprising sequentially administering to the subject two or more immunogenic compositions described herein, wherein each immunogenic composition comprises an inactivated influenza B virus and a CpG oligonucleotide adjuvant described herein, wherein each inactivated influenza B virus comprises a mosaic HA, and wherein each mosaic HA is different from each other. In some embodiments, provided herein are methods of inducing an immune response in a subject (e.g., human subject) that is capable of cross-reacting with a plurality of influenza B virus strains and lineages, comprising sequentially administering to the subject two or more immunogenic compositions described herein, wherein each immunogenic composition comprises an inactivated split influenza B virus and a CpG oligonucleotide adjuvant described herein, wherein each inactivated split influenza B virus comprises a mosaic HA, wherein each mosaic HA is different from each other. In some embodiments, each mosaic HA is immunologically distinct from each other. In some embodiments, two mosaic HAs are immunologically distinct from each other if there is no detectable cross-reactivity in an immunoassay described herein or known to one of skill in the art. In some embodiments, two mosaic HAs are immunologically distinct from each other if there is no detectable cross-reactivity in a hemagglutinin inhibition assay described herein or known to one of skill in the art. In some embodiments, two mosaic HAs are immunologically distinct from each other if there is no detectable cross-reactivity in an immunoassay described herein or known to one of skill in the art and a hemagglutinin inhibition assay described herein or known to one of skill in the art. In some embodiments, each mosaic HA comprises a different amino acid sequence. In some embodiments, each mosaic HA is derived from a different influenza B virus HA. In some embodiments, each immunogenic composition comprises an aluminum salt. In some embodiments, each immunogenic composition does not comprise an aluminum salt. In some embodiments, an aluminum salt is administered to the subject concurrently or about 1 hour(or about 45 minutes, about 30 minutes, or about 15 minutes) before or after the administration of the first immunogenic composition. In some embodiments, an aluminum salt is administered to the subject concurrently or about 1 hour (or about 45 minutes, about 30 minutes, or about 15 minutes) before or after the administration of the second immunogenic composition. In some embodiments, each immunogenic composition is administered to the subject from about 2 months to about 9 months apart from another immunogenic composition. In some embodiments, each immunogenic composition is administered to the subject from about 3 months to about 9 months or about 3 months to about 6 months apart from another immunogenic composition. In some embodiments, each immunogenic composition is administered to the subject from about 21 days to about 60 days apart from another immunogenic composition. In some embodiments, each immunogenic composition is administered to the subject from about 60 to about 120 days apart from another immunogenic composition. In some embodiments, each immunogenic composition is administered to the subject from about 21 days to about 120 days apart from another immunogenic composition. In some embodiments, each immunogenic composition is administered to the subject from about 21 days to about 6 months apart from another immunogenic composition. In some embodiments, each immunogenic composition is administered to the subject intramuscularly or intranasally.

[0198] In some embodiments, provided herein is a method of inducing an immune response to influenza B viruses (e.g., a cross-reactive immune response to influenza B viruses) in a subject (e.g., human subject), comprising: (a) administering to the subject a first immunogenic composition comprising a first mosaic HA described herein and a CpG oligonucleotide adjuvant described herein; and (b) a certain period of time after administration of the first immunogenic composition to the subject, administering to the subject a second immunogenic composition comprising a second mosaic HA described herein and a CpG oligonucleotide adjuvant described herein, wherein the first mosaic HA and the second mosaic HA are different from each other. In some embodiments, the first mosaic HA comprises the HA ectodomain of a first influenza B virus HA with amino acid changes (e.g., substitutions, deletions, and / or additions) in one, two, three, or four of the 120 loop, 150 loop, 160 loop, and 190 helix and the second mosaic HA comprises the HA ectodomain of a second influenza B virus HA with amino acid changes (e.g., substitutions, deletions, and / or additions) in one, two, three, or four of the 120 loop, 150 loop, 160 loop, and 190 helix, wherein the first influenza B virus HA is different from the second influenza B virus HA. In some embodiments, the first influenza B virus HA is from a different influenza B viruslineage than the second influenza B virus HA. For example, the first influenza B virus HA is from the A / Victoria lineage (e.g., B / Victoria / 2 / 1987-like lineage) and the second influenza B virus is from the A / Yamagata lineage (e.g., B / Yamagata / 16 / 1988-like lineage). In some embodiments, the first influenza B virus HA is from a different influenza B virus strain than the second influenza B virus HA. In some embodiments, the first influenza B virus HA is from one influenza B virus strain disclosed herein (e.g., in Example 1) and the second influenza B virus HA is from a different influenza B virus strain disclosed herein (e.g., in Example 1). In some embodiments, the first influenza B virus HA is from one influenza B virus strain disclosed in FIG. 1G or 1H and the second influenza B virus HA is from a different influenza B virus strain disclosed in FIG. 1G or 1H. In some embodiments, the first and second immunogenic compositions each comprise an aluminum salt. The aluminum salt in the first and second immunogenic compositions may or may not be the same. In some embodiments, the first and second immunogenic compositions do not comprise an aluminum salt. In some embodiments, an aluminum salt is administered to the subject concurrently or about 1 hour (or about 45 minutes, about 30 minutes, or about 15 minutes) before or after the administration of the first immunogenic composition. In some embodiments, an aluminum salt is administered to the subject concurrently or about 1 hour (or about 45 minutes, about 30 minutes, or about 15 minutes) before or after the administration of the second immunogenic composition. In some embodiments, the first and second immunogenic compositions are administered to the subject from about 2 months to about 9 months apart from each other. In some embodiments, the first and second immunogenic compositions are administered to the subject from about 3 months to about 9 months or about 3 months to about 6 months apart from each other. In some embodiments, each immunogenic composition is administered to the subject from about 21 days to about 60 days apart from another immunogenic composition. In some embodiments, each immunogenic composition is administered to the subject from about 21 days to about 120 days apart from another immunogenic composition. In some embodiments, each immunogenic composition is administered to the subject from about 21 days to about 6 months apart from another immunogenic composition. In some embodiments, the method further comprises administering to the subject a third immunogenic composition a certain time after the administration of the second immunogenic composition to the subject, wherein the third immunogenic composition comprises a third mosaic HA described herein and a CpG oligonucleotide adjuvant described herein, wherein the third mosaic HA is different than first mosaic HA and the second mosaic HA. In some embodiments, the first mosaic HA comprises the HA ectodomain of a first influenza B virusHA with amino acid changes (e.g., substitutions, deletions, and / or additions) in one, two, three, or four of the 120 loop, 150 loop, 160 loop, and 190 helix, the second mosaic HA comprises the HA ectodomain of a second influenza B virus HA with amino acid changes (e.g., substitutions, deletions, and / or additions) in one, two, three, or four of the 120 loop, 150 loop, 160 loop, and 190 helix, and the third mosaic HA comprises the HA ectodomain of a third influenza B virus HA with amino acid changes (e.g., substitutions, deletions, and / or additions) in one, two, three, or four of the 120 loop, 150 loop, 160 loop, and 190 helix, wherein the first influenza B virus HA, the second influenza B virus HA, and the third influenza B virus HA are different from each other. In some embodiments, the first influenza B virus HA, the second influenza B virus HA, and the third influenza B virus HA are from different influenza B virus lineages. In some embodiments, the first influenza B virus HA, the second influenza B virus HA, and the third influenza B virus HA are from different influenza B virus strains. In some embodiments, the first influenza B virus HA, the second influenza B virus HA, the third influenza B virus HA are each from a different influenza B virus strain disclosed herein (e.g., in Example 1). In some embodiments, the first influenza B virus HA, the second influenza B virus HA, the third influenza B virus HA are each from a different influenza B virus strain disclosed in FIG. 1G or 1H. In some embodiments, each immunogenic composition is administered to the subject intramuscularly or intranasally. In some embodiments, the mosaic HA in an immunogenic composition is administered to the subject at a dose provided herein. In some embodiments, the CpG oligonucleotide adjuvant in an immunogenic composition is administered to the subject at a dose provided herein.

[0199] In some embodiments, provided herein is a method of inducing an immune response to influenza B viruses (e.g., a cross-reactive immune response to influenza B viruses) in a subject (e.g., a human subject), comprising: (a) administering to the subject a first immunogenic composition comprising a first inactivated influenza virus (e.g., influenza B virus) and a CpG oligonucleotide adjuvant described herein, wherein the first inactivated influenza virus comprises a first mosaic HA described herein; and (b) a certain period of time after administration of the first immunogenic composition to the subject, administering to the subject a second immunogenic composition comprising a second inactivated influenza B virus (e.g., influenza B virus) and a CpG oligonucleotide adjuvant described herein, wherein the second inactivated influenza B virus comprises a second mosaic HA described herein, and wherein the first and the second mosaic HA are different from each other. In some embodiments, the first mosaic HA comprises the HA ectodomain of a first influenza B virus HA with amino acid changes (e.g., substitutions, deletions, and / or additions) in one, two,I l lthree, or four of the 120 loop, 150 loop, 160 loop, and 190 helix and the second mosaic HA comprises the HA ectodomain of a second influenza B virus HA with amino acid changes (e.g., substitutions, deletions, and / or additions) in one, two, three, or four of the 120 loop, 150 loop, 160 loop, and 190 helix, wherein the first influenza B virus HA is different from the second influenza B virus HA. In some embodiments, the first influenza B virus HA is from a different influenza B virus lineage than the second influenza B virus HA. For example, the first influenza B virus HA is from the A / Victoria lineage (e.g., B / Victoria / 2 / 1987-like lineage) and the second influenza B virus is from the A / Yamagata lineage (e.g., B / Yamagata / 16 / 1988-like lineage). In some embodiments, the first influenza B virus HA is from a different influenza B virus strain than the second influenza B virus HA. In some embodiments, the first influenza B virus HA is from one influenza B virus strain disclosed herein (e.g., in Example 1) and the second influenza B virus HA is from a different influenza B virus strain disclosed herein (e.g., in Example 1). In some embodiments, the first influenza B virus HA is from one influenza B virus strain disclosed in FIG. 1G or 1H and the second influenza B virus HA is from a different influenza B virus strain disclosed in FIG. 1G or 1H. In some embodiments, the first and second immunogenic compositions each comprise an aluminum salt. The aluminum salt in the first and second immunogenic compositions may or may not be the same. In some embodiments, the first and second immunogenic compositions do not comprise an aluminum salt. In some embodiments, an aluminum salt is administered to the subject concurrently or about 1 hour (or about 45 minutes, about 30 minutes, or about 15 minutes) before or after the administration of the first immunogenic composition. In some embodiments, an aluminum salt is administered to the subject concurrently or about 1 hour (or about 45 minutes, about 30 minutes, or about 15 minutes) before or after the administration of the second immunogenic composition. In some embodiments, the first and second immunogenic compositions are administered to the subject from about 2 months to about 9 months apart from each other. In some embodiments, the first and second immunogenic compositions are administered to the subject from about 3 months to about 9 months or about 3 months to about 6 months apart from each other. In some embodiments, the first and second immunogenic compositions are administered to the subject from about 60 to about 120 days apart from each other. In some embodiments, the method further comprises administering to the subject a third immunogenic composition a certain time after the administration of the second immunogenic composition to the subject, wherein the third immunogenic composition comprises a third inactivated influenza virus (e.g., influenza B virus) and a CpG oligonucleotide adjuvant described herein, wherein the third inactivatedinfluenza virus comprises a third mosaic HA described herein, and wherein the first mosaic HA, the second mosaic HA, and third mosaic HA are different from each other. In some embodiments, the first mosaic HA comprises the HA ectodomain of a first influenza B virus HA with amino acid changes (e.g., substitutions, deletions, and / or additions) in one, two, three, or four of the 120 loop, 150 loop, 160 loop, and 190 helix, the second mosaic HA comprises the HA ectodomain of a second influenza B virus HA with amino acid changes (e.g., substitutions, deletions, and / or additions) in one, two, three, or four of the 120 loop, 150 loop, 160 loop, and 190 helix, and the third mosaic HA comprises the HA ectodomain of a third i...

Claims

We Claim:

1. An immunogenic composition, comprising: a) a mosaic hemagglutinin (HA) comprising an HA ectodomain of an influenza B virus HA, wherein the HA ectodomain comprises (A) an HA stalk domain of the influenza B virus HA, and (B) an HA globular head domain of the influenza B virus HA with amino acid substitutions in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain, and 0, 1, 2, or 3 compensatory amino acid substitutions outside of the 120 loop, the 150 loop, the 160 loop, and the 190 helix, wherein:(i) the amino acid substitutions in the 120 loop consist of 2, 3, 4, 5, 6, 7, 8, 9, or10 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the 120 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA;(ii) the amino acid substitutions in the 150 loop consist of 2, 3, 4, 5, 6, or 7 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the 150 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA;(iii) the amino acid substitutions in the 160 loop consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 160 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA; and(iv) the amino acid substitutions in the 190 helix consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 190 helix of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA; b) a CpG oligonucleotide adjuvant comprising an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84); and c) an aluminum salt.

2. The immunogenic composition according to claim 1, wherein the mosaic HA further comprises transmembrane and cytoplasmic domains of the influenza B virus HA.

3. The immunogenic composition according to claim 1, wherein the mosaic HA further comprises a trimerization domain.

4. An immunogenic composition, comprising: a) an inactivated influenza B virus comprising a mosaic hemagglutinin (HA), wherein the mosaic HA comprises an HA ectodomain of an influenza B virus HA, wherein the HA ectodomain comprises (A) an HA stalk domain of the influenza B virus HA, and (B) an HA globular head domain of the influenza B virus HA with amino acid substitutions in the 120 loop, 150 loop, 160 loop, and 190 helix, and 0, 1, 2, or 3 compensatory amino acid substitutions outside of the 120 loop, the 150 loop, the 160 loop, and the 190 helix, wherein:(i) the amino acid substitutions in the 120 loop consist of 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the 120 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA;(ii) the amino acid substitutions in the 150 loop consist of 2, 3, 4, 5, 6, or 7 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the 150 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA;(iii) the amino acid substitutions in the 160 loop consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 160 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA; and(iv) the amino acid substitutions in the 190 helix consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 190 helix of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA;b) a CpG oligonucleotide adjuvant comprising an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84); and c) an aluminum salt.

5. An immunogenic composition, comprising: a) a inactivated split influenza B virus comprising a mosaic hemagglutinin (HA), wherein the mosaic HA comprises an HA ectodomain of an influenza B virus HA, wherein the HA ectodomain comprises (A) an HA stalk domain of the influenza B virus HA, and (B) an HA globular head domain of the influenza B virus HA with amino acid substitutions in the 120 loop, 150 loop, 160 loop, and 190 helix, and 0, 1, 2, or 3 compensatory amino acid substitutions outside of the 120 loop, the 150 loop, the 160 loop, and the 190 helix, wherein:(i) the amino acid substitutions in the 120 loop consist of 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the 120 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA;(ii) the amino acid substitutions in the 150 loop consist of 2, 3, 4, 5, 6, or 7 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the 150 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA;(iii) the amino acid substitutions in the 160 loop consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 160 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA; and(iv) the amino acid substitutions in the 190 helix consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 190 helix of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA;b) a CpG oligonucleotide adjuvant comprising an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84); and c) an aluminum salt.

6. The immunogenic composition according to claim 4 or 5, wherein the mosaic HA further comprises transmembrane and cytoplasmic domains of the influenza B virus HA.

7. The immunogenic composition according to any one of claims 1 to 6, wherein the influenza B virus is B / Yamagata / 16 / 1988.

8. The immunogenic composition according to any one of claims 1 to 6, wherein the influenza B virus HA ectodomain is the ectodomain of influenza virus B / Yamagata / 16 / 1988 HA.

9. The immunogenic composition according to any one of claims 1 to 6, wherein the influenza B virus is B / Phuket / 3073 / 2013.

10. The immunogenic composition according to any one of claims 1 to 6, wherein the influenza B virus HA ectodomain is the ectodomain of influenza virus B / Phuket / 3073 / 2013 HA11. The immunogenic composition according to any one of claims 1 to 6, wherein the influenza B virus is B / Brisbane / 60 / 2008.

12. The immunogenic composition according to any one of claims 1 to 6, wherein the influenza B virus HA ectodomain is the ectodomain of influenza virus B / Brisbane / 60 / 2008 HA.

13. The immunogenic composition according to claim 1 to 8, wherein:(i) the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the amino acid sequence TIP and the amino acid sequence of SEQ ID NO:1 of the 120 loop of the globular head domain of the influenza B virus HA with aminoacid residues found in a corresponding region of the globular head domain of the influenza A virus HA;(ii) the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the amino acid sequence of SEQ ID NO: 2 of the 150 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA;(iii) the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the amino acid sequence of SEQ ID NO: 3 of the 160 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA; and(iv) the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the amino acid sequence of SEQ ID NO: 4 of the 190 helix of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA.

14. The immunogenic composition according to claim 1 to 6, 9 or 10, wherein:(i) the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the amino acid sequence TTP and the amino acid sequence of SEQ ID NO: 29 of the 120 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA;(ii) the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the amino acid sequence of SEQ ID NO: 30 of the 150 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA;(iii) the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the amino acid sequence of SEQ ID NO: 31 of the 160 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA; and(iv) the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the amino acid sequence of SEQ ID NO: 32 of the 190 helix of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA.

15. The immunogenic composition according to claim 1 to 6, 11, or 12, wherein:(i) the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the amino acid sequence KIP and the amino acid sequence of SEQ ID NO: 21 of the 120 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA;(ii) the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the amino acid sequence of SEQ ID NO: 22 of the 150 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA;(iii) the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the amino acid sequence of SEQ ID NO: 23 of the 160 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA; and(iv) the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the amino acid sequence of SEQ ID NO: 24 of the 190 helix of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA.

16. The immunogenic composition according to any one of claims 1 to 15, wherein the influenza A virus HA is an exotic avian influenza A virus HA to which humans are naive.

17. The immunogenic composition of according to any one of claims 1 to 16, wherein the influenza A virus is an influenza A virus H5, H8, Hl 1, or Hl 3 subtype.

18. The immunogenic composition according to any one of claims 1 to 17, wherein the influenza A virus HA is influenza virus A / Vietnam / 1203 / 2004 HA, influenza virus A / mallard / Sweden / 24 / 2002 HA, influenza virus A / shoveler / Netherlands / 18 / 99 HA, or influenza virus A / black-headed gull / / Sweden / l / 1999 HA.

19. The immunogenic composition according to claim 1 to 8, wherein:(A) (i) the amino acid sequence TIP and the amino acid sequence of SEQ ID NO: 1 of the 120 loop of the globular head domain of the influenza B virus HA are substituted with the amino acid sequence FIP and the amino acid sequence of SEQ ID NO: 5, respectively;(ii) the amino acid sequence of SEQ ID NO: 2 of the 150 loop of the globular head domain of the influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 6;(iii) the amino acid sequence of SEQ ID NO: 3 of the 160 loop of the globular head domain of the influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 7; and(iv) the amino acid sequence of SEQ ID NO: 4 of the 190 helix of the globular head domain of the influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 8;(B) (i) the amino acid sequence TIP and the amino acid sequence of SEQ ID NO: 1 of the 120 loop of the globular head domain of the influenza B virus HA are substituted with the amino acid sequence HIP and the amino acid sequence of SEQ ID NO: 9, respectively;(ii) the amino acid sequence of SEQ ID NO: 2 of the 150 loop of the globular head domain of the influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 10;(iii) the amino acid sequence of SEQ ID NO: 3 of the 160 loop of the globular head domain of the influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 11; and(iv) the amino acid sequence of SEQ ID NO: 4 of the 190 helix of the globular head domain of the influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 12; or(C) (i) the amino acid sequence TIP and the amino acid sequence of SEQ ID NO: 1 of the 120 loop of the globular head domain of the influenza B virus HA are substituted with the amino acid sequence LIP and the amino acid sequence of SEQ ID NO: 13, respectively;(ii) the amino acid sequence of SEQ ID NO: 2 of the 150 loop of the globular head domain of the influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 14;(iii) the amino acid sequence of SEQ ID NO: 3 of the 160 loop of the globular head domain of the influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 15; and(iv) the amino acid sequence of SEQ ID NO: 4 of the 190 helix of the globular head domain of the influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 16; or(D) (i) the amino acid sequence TIP and the amino acid sequence of SEQ IDNO: 1 of the 120 loop of the globular head domain of the influenza B virus HA are substituted with the amino acid sequence NIP and the amino acid sequence of SEQ ID NO: 17, respectively;(ii) the amino acid sequence of SEQ ID NO: 2 of the 150 loop of the globular head domain of the influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 18;(iii) the amino acid sequence of SEQ ID NO: 3 of the 160 loop of the globular head domain of the influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 19; and(iv) the amino acid sequence of SEQ ID NO: 4 of the 190 helix of the globular head domain of the influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 20.

20. The immunogenic composition according to claim 1 to 6, 9, or 10, wherein:(i) the amino acid sequence TTP and the amino acid sequence of SEQ ID NO: 29 of the 120 loop of the globular head domain of the influenza B virus HA are substituted with the amino acid sequence FTP and the amino acid sequence of SEQ ID NO: 33, respectively;(ii) the amino acid sequence of SEQ ID NO: 30 of the 150 loop of the globular head domain of the influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 34;(iii) the amino acid sequence of SEQ ID NO: 31 of the 160 loop of the globular head domain of the influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 35; and(iv) the amino acid sequence of SEQ ID NO: 32 of the 190 helix of the globular head domain of the influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 36.

21. The immunogenic composition according to claim 1 to 6, 11, or 12, wherein:(i) the amino acid sequence KIP and the amino acid sequence of SEQ ID NO: 21 of the 120 loop of the globular head domain of the influenza B virus HA are substituted with the amino acid sequence NIP and the amino acid sequence of SEQ ID NO: 25, respectively;(ii) the amino acid sequence of SEQ ID NO: 22 of the 150 loop of the globular head domain of the influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 26;(iii) the amino acid sequence of SEQ ID NO: 23 of the 160 loop of the globular head domain of the influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 27; and(iv) the amino acid sequence of SEQ ID NO: 24 of the 190 helix of the globular head domain of the influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 28 or 37.

22. An immunogenic composition, comprising: a) a mosaic hemagglutinin (HA) comprising the amino acid sequence of SEQ ID NO: 38, 40, 42, 44, 46, or 48; b) a CpG oligonucleotide adjuvant comprising an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84); and c) an aluminum salt.

23. An immunogenic composition, comprising: a) an inactivated influenza B virus comprising a mosaic hemagglutinin (HA), wherein the mosaic HA comprises the amino acid sequence of SEQ ID NO: 38, 40, 42, 44, 46, or 48; b) a CpG oligonucleotide adjuvant comprising an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84); andc) an aluminum salt.

24. An immunogenic composition, comprising: a) an inactivated split influenza B virus comprising a mosaic hemagglutinin (HA), wherein the mosaic HA comprises the amino acid sequence of SEQ ID NO: 38, 40, 42, 44, 46, or 48; b) a CpG oligonucleotide adjuvant comprising an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84); and c) an aluminum salt.

25. An immunogenic composition, comprising: a) a mosaic hemagglutinin (HA) comprising an HA ectodomain of an influenza B virus HA, wherein the HA ectodomain comprises (A) an HA stalk domain of the influenza B virus HA, and (B) an HA globular head domain of the influenza B virus HA with amino acid substitutions in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain, and 0, 1, 2, or 3 compensatory amino acid substitutions outside of the 120 loop, the 150 loop, the 160 loop, and the 190 helix, and wherein the ectodomain of the mosaic HA comprises an amino acid sequence that is at least 95% identical the amino acid sequence of SEQ ID NO: 38, 40, 42, 44, 46, or 48; b) a CpG oligonucleotide adjuvant comprising an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84); and c) an aluminum salt.

26. An immunogenic composition, comprising: a) an inactivated influenza B virus comprising a mosaic hemagglutinin (HA), wherein the mosaic HA comprises an HA ectodomain of an influenza B virus HA, wherein the HA ectodomain comprises (A) an HA stalk domain of the influenza B virus HA, and (B) an HA globular head domain of the influenza B virus HA with amino acid substitutions in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain, and 0, 1, 2, or 3 compensatory amino acid substitutions outside of the 120 loop, the 150 loop, the 160 loop, and the 190 helix, and wherein the mosaic HA comprises an amino acid sequence that is at least 95% identical the amino acid sequence of SEQ ID NO: 38, 40, 42, 44, 46, or 48;b) a CpG oligonucleotide adjuvant comprising an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84); and c) an aluminum salt.

27. An immunogenic composition, comprising: a) an inactivated split influenza B virus comprising a mosaic hemagglutinin (HA), wherein the mosaic HA comprises an HA ectodomain of an influenza B virus HA, wherein the HA ectodomain comprises (A) an HA stalk domain of the influenza B virus HA, and (B) an HA globular head domain of the influenza B virus HA with amino acid substitutions in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain, and 0, 1, 2, or 3 compensatory amino acid substitutions outside of the 120 loop, the 150 loop, the 160 loop, and the 190 helix, and wherein the mosaic HA comprises an amino acid sequence that is at least 95% identical the amino acid sequence of SEQ ID NO: 38, 40, 42, 44, 46, or 48; b) a CpG oligonucleotide adjuvant comprising an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84); and c) an aluminum salt.

28. The immunogenic composition according to any one of claims 1 to 27, wherein the oligonucleotide comprises the nucleotide sequence of 5’- TGACTGTGAACGTTCGAGATGA-3’ (SEQ ID NO: 85).

29. The immunogenic composition according to any one of claims 1 to 28, wherein the oligonucleotide is 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, or 35 nucleotides in length.

30. The immunogenic composition according to any one of claims 1 to 29, wherein the oligonucleotide is a single stranded oligodeoxynucleotide.

31. The immunogenic composition according to any one of claims 1 to 29, wherein the oligonucleotide is fully RNA or is an RNA / DNA chimera.

32. The immunogenic composition according to any one of claims 1 to 31, wherein the oligonucleotide comprises only phosphorothioate linkages, or a combination of one or more phosphodiester linkages and one or more phosphorothioate linkages.

33. The immunogenic composition according to any one of claims 1 to 32, wherein the aluminum salt comprises one or more selected from the group consisting of amorphous aluminum hydroxyphosphate sulfate, aluminum hydroxide, aluminum phosphate, and potassium aluminum sulfate.

34. The immunogenic composition according to any one of claims 1 to 32, wherein the aluminum salt comprises aluminum hydroxide or aluminum phosphate.

35. A method of preventing influenza virus disease in a subject, comprising administering to the subject the immunogenic composition of any one of claims 1 to 34.

36. A method of immunizing a subject against influenza virus disease, comprising administering to the subject the immunogenic composition of any one of claims 1 to 34.

37. A method of inducing a cross-reactive immune response to at least two influenza B viruses in a subject, comprising administering to the subject the immunogenic composition of any one of claims 1 to 34.

38. The method according to any one of claims 34 to 37, wherein the immunogenic composition is administered intramuscularly or intranasally to the subject.

39. A method of preventing influenza virus disease in a subject, comprising: a) administering to the subject a first immunogenic composition comprising inactivated influenza B virus #1, a CpG oligonucleotide adjuvant, and an aluminum salt, wherein inactivated influenza B virus #1 comprises mosaic hemagglutinin (HA) #1, wherein the mosaic HA #1 comprises a first HA ectodomain of a first influenza B virus HA, wherein the first HA ectodomain comprises (A) an HA stalk domain of the first influenza B virus HA, and (B) an HA globular head domain of the first influenza B virus HA with amino acid substitutions in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain, and 0, 1, 2, or 3 compensatory amino acid substitutions outside of the 120 loop, the 150 loop, the 160 loop, and the 190 helix, and wherein:(i) the amino acid substitutions in the 120 loop consist of 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the 120 loop of the HA globular head domain of the first influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of a first influenza A virus HA;(ii) the amino acid substitutions in the 150 loop consist of 2, 3, 4, 5, 6, or 7 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the 150 loop of the HA globular head domain of the first influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the first influenza A virus HA;(iii) the amino acid substitutions in the 160 loop consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 160 loop of the HA globular head domain of the first influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the first influenza A virus HA; and(iv) the amino acid substitutions in the 190 helix consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 190 helix of the HA globular head domain of the first influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the first influenza A virus HA; and b) a certain period of time after administration of the first immunogenic composition to the subject, administering to the subject a second immunogenic composition comprising inactivated influenza B virus #2, a CpG oligonucleotide adjuvant, and an aluminum salt, wherein inactivated influenza B virus #2 comprises mosaic HA #2, wherein the mosaic HA #2 comprises a second HA ectodomain of a second influenza B virus HA, wherein the second HA ectodomain comprises (A) an HA stalk domain of the second influenza B virus HA, and (B) an HA globular head domain of the second influenza B virus HA with amino acid substitutions in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain, and 0, 1, 2, or 3 compensatory amino acid substitutions outside of the 120 loop, the 150 loop, the 160 loop, and the 190 helix, and wherein:(i) the amino acid substitutions in the 120 loop consist of 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the 120 loop of the HA globular headdomain of the second influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of a second influenza A virus HA;(ii) the amino acid substitutions in the 150 loop consist of 2, 3, 4, 5, 6, or 7 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the 150 loop of the HA globular head domain of the second influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the second influenza A virus HA;(iii) the amino acid substitutions in the 160 loop consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 160 loop of the HA globular head domain of the second influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the second influenza A virus HA; and(iv) the amino acid substitutions in the 190 helix consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 190 helix of the HA globular head domain of the second influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the second influenza A virus HA, and wherein the first HA ectodomain and the second HA ectodomain comprise different amino acid sequences, and wherein each CpG oligonucleotide adjuvant comprises an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84).

40. A method of immunizing a subject against influenza virus disease, comprising: a) administering to the subject a first immunogenic composition comprising inactivated influenza B virus #1, a CpG oligonucleotide adjuvant, and an aluminum salt, wherein inactivated influenza B virus #1 comprises mosaic hemagglutinin (HA) #1, wherein the mosaic HA #1 comprises a first HA ectodomain of a first influenza B virus HA, wherein the first HA ectodomain comprises (A) an HA stalk domain of the first influenza B virus HA, and (B) an HA globular head domain of the first influenza B virus HA with amino acid substitutions in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain, and 0, 1, 2, or 3 compensatory amino acid substitutions outside of the 120 loop, the 150 loop, the 160 loop, and the 190 helix, and wherein:(i) the amino acid substitutions in the 120 loop consist of 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the 120 loop of the HA globular head domain of the first influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of a first influenza A virus HA;(ii) the amino acid substitutions in the 150 loop consist of 2, 3, 4, 5, 6, or 7 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the 150 loop of the HA globular head domain of the first influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the first influenza A virus HA;(iii) the amino acid substitutions in the 160 loop consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 160 loop of the HA globular head domain of the first influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the first influenza A virus HA; and(iv) the amino acid substitutions in the 190 helix consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 190 helix of the HA globular head domain of the first influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the first influenza A virus HA; and b) a certain period of time after administration of the first immunogenic composition to the subject, administering to the subject a second immunogenic composition comprising inactivated influenza B virus #2, a CpG oligonucleotide adjuvant, and an aluminum salt, wherein inactivated influenza B virus #2 comprises mosaic HA #2, wherein the mosaic HA #2 comprises a second HA ectodomain of a second influenza B virus HA, wherein the second HA ectodomain comprises (A) an HA stalk domain of the second influenza B virus HA, and (B) an HA globular head domain of the second influenza B virus HA with amino acid substitutions in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain, and 0, 1, 2, or 3 compensatory amino acid substitutions outside of the 120 loop, the 150 loop, the 160 loop, and the 190 helix, and wherein:(i) the amino acid substitutions in the 120 loop consist of 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the 120 loop of the HA globular headdomain of the second influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of a second influenza A virus HA;(ii) the amino acid substitutions in the 150 loop consist of 2, 3, 4, 5, 6, or 7 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the 150 loop of the HA globular head domain of the second influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the second influenza A virus HA;(iii) the amino acid substitutions in the 160 loop consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 160 loop of the HA globular head domain of the second influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the second influenza A virus HA; and(iv) the amino acid substitutions in the 190 helix consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 190 helix of the HA globular head domain of the second influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the second influenza A virus HA, and wherein the first HA ectodomain and the second HA ectodomain comprise different amino acid sequences, and wherein each CpG oligonucleotide adjuvant comprises an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84).

41. A method of inducing a cross-reactive immune response to at least two influenza B viruses in a subject, comprising: a) administering to the subject a first immunogenic composition comprising inactivated influenza B virus #1, a CpG oligonucleotide adjuvant, and an aluminum salt, wherein inactivated influenza B virus #1 comprises mosaic hemagglutinin (HA) #1, wherein the mosaic HA #1 comprises a first HA ectodomain of a first influenza B virus HA, wherein the first HA ectodomain comprises (A) an HA stalk domain of the first influenza B virus HA, and (B) an HA globular head domain of the first influenza B virus HA with amino acid substitutions in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular headdomain, and 0, 1, 2, or 3 compensatory amino acid substitutions outside of the 120 loop, the 150 loop, the 160 loop, and the 190 helix, and wherein:(i) the amino acid substitutions in the 120 loop consist of 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the 120 loop of the HA globular head domain of the first influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of a first influenza A virus HA;(ii) the amino acid substitutions in the 150 loop consist of 2, 3, 4, 5, 6, or 7 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the 150 loop of the HA globular head domain of the first influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the first influenza A virus HA;(iii) the amino acid substitutions in the 160 loop consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 160 loop of the HA globular head domain of the first influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the first influenza A virus HA; and(iv) the amino acid substitutions in the 190 helix consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 190 helix of the HA globular head domain of the first influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the first influenza A virus HA; and b) a certain period of time after administration of the first immunogenic composition to the subject, administering to the subject a second immunogenic composition comprising inactivated influenza B virus #2, a CpG oligonucleotide adjuvant, and an aluminum salt, wherein inactivated influenza B virus #2 comprises mosaic HA #2, wherein the mosaic HA #2 comprises a second HA ectodomain of a second influenza B virus HA, wherein the second HA ectodomain comprises (A) an HA stalk domain of the second influenza B virus HA, and (B) an HA globular head domain of the second influenza B virus HA with amino acid substitutions in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain, and 0, 1, 2, or 3 compensatory amino acid substitutions outside of the 120 loop, the 150 loop, the 160 loop, and the 190 helix, and wherein:(i) the amino acid substitutions in the 120 loop consist of 2, 3, 4, 5, 6, 7, 8, 9, or10 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3,4, 5, 6, 7, 8, 9, or 10 amino acid residues in the 120 loop of the HA globular head domain of the second influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of a second influenza A virus HA;(ii) the amino acid substitutions in the 150 loop consist of 2, 3, 4, 5, 6, or 7 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the 150 loop of the HA globular head domain of the second influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the second influenza A virus HA;(iii) the amino acid substitutions in the 160 loop consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 160 loop of the HA globular head domain of the second influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the second influenza A virus HA; and(iv) the amino acid substitutions in the 190 helix consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 190 helix of the HA globular head domain of the second influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the second influenza A virus HA, and wherein the first HA ectodomain and the second HA ectodomain comprise different amino acid sequences, and wherein each CpG oligonucleotide adjuvant comprises an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84).

42. The method according to any one of claims 39 to 41, wherein the method further comprises administering to the subject a third immunogenic composition a certain time after the administration of the second immunogenic composition to the subject, wherein the third immunogenic composition comprises inactivated influenza virus #3, a CpG oligonucleotide adjuvant, and an aluminum salt, wherein the inactivated influenza virus #3 comprises mosaic HA #3, wherein the mosaic HA #3 comprises a third HA ectodomain of a third influenza B virus HA, wherein the third HA ectodomain comprises (A) an HA stalk domain of the third influenza B virus HA, and (B) an HA globular head domain of the third influenza B virus HA with amino acid substitutions in the 120 loop, 150 loop, 160 loop, and 190 helix of the HAglobular head domain, and 0, 1, 2, or 3 compensatory amino acid substitutions outside of the 120 loop, the 150 loop, the 160 loop, and the 190 helix, and wherein:(i) the amino acid substitutions in the 120 loop consist of 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the 120 loop of the HA globular head domain of the third influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of a third influenza A virus HA;(ii) the amino acid substitutions in the 150 loop consist of 2, 3, 4, 5, 6, or 7 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the 150 loop of the HA globular head domain of the third influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the third influenza A virus HA;(iii) the amino acid substitutions in the 160 loop consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 160 loop of the HA globular head domain of the third influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the third influenza A virus HA; and(iv) the amino acid substitutions in the 190 helix consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 190 helix of the HA globular head domain of the third influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the third influenza A virus HA, and wherein the first HA ectodomain, the second HA ectodomain, and the third HA ectodomain each comprise different amino acid sequences, and wherein each CpG oligonucleotide adjuvant comprises an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84).

43. A method of preventing influenza virus disease in a subject, comprising: a) administering to the subject a first immunogenic composition comprising inactivated split influenza B virus #1, a CpG oligonucleotide adjuvant, and an aluminum salt, wherein inactivated split influenza B virus #1 comprises mosaic hemagglutinin (HA) #1, wherein the mosaic HA #1 comprises a first HA ectodomain of a first influenza B virus HA,wherein the first HA ectodomain comprises (A) an HA stalk domain of the first influenza B virus HA, and (B) an HA globular head domain of the first influenza B virus HA with amino acid substitutions in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain, and 0, 1, 2, or 3 compensatory amino acid substitutions outside of the 120 loop, the 150 loop, the 160 loop, and the 190 helix, and wherein:(i) the amino acid substitutions in the 120 loop consist of 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the 120 loop of the HA globular head domain of the first influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of a first influenza A virus HA;(ii) the amino acid substitutions in the 150 loop consist of 2, 3, 4, 5, 6, or 7 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the 150 loop of the HA globular head domain of the first influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the first influenza A virus HA;(iii) the amino acid substitutions in the 160 loop consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 160 loop of the HA globular head domain of the first influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the first influenza A virus HA; and(iv) the amino acid substitutions in the 190 helix consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 190 helix of the HA globular head domain of the first influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the first influenza A virus HA; and b) a certain period of time after administration of the first immunogenic composition to the subject, administering to the subject a second immunogenic composition comprising inactivated split influenza B virus #2, a CpG oligonucleotide adjuvant, and an aluminum salt, wherein inactivated split influenza B virus #2 comprises mosaic HA #2, wherein the mosaic HA #2 comprises a second HA ectodomain of a second influenza B virus HA, wherein the second HA ectodomain comprises (A) an HA stalk domain of the second influenza B virus HA, and (B) an HA globular head domain of the second influenza B virus HA with amino acid substitutions in the 120 loop, 150 loop, 160 loop, and 190 helix of theHA globular head domain, and 0, 1, 2, or 3 compensatory amino acid substitutions outside of the 120 loop, the 150 loop, the 160 loop, and the 190 helix, and wherein:(i) the amino acid substitutions in the 120 loop consist of 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the 120 loop of the HA globular head domain of the second influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of a second influenza A virus HA;(ii) the amino acid substitutions in the 150 loop consist of 2, 3, 4, 5, 6, or 7 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the 150 loop of the HA globular head domain of the second influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the second influenza A virus HA;(iii) the amino acid substitutions in the 160 loop consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 160 loop of the HA globular head domain of the second influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the second influenza A virus HA; and(iv) the amino acid substitutions in the 190 helix consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 190 helix of the HA globular head domain of the second influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the second influenza A virus HA, and wherein the first HA ectodomain and the second HA ectodomain comprise different amino acid sequences, and wherein each CpG oligonucleotide adjuvant comprises an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84).

44. A method of immunizing a subject against influenza virus disease, comprising: a) administering to the subject a first immunogenic composition comprising inactivated split influenza B virus #1, a CpG oligonucleotide adjuvant, and an aluminum salt, wherein inactivated split influenza B virus #1 comprises mosaic hemagglutinin (HA) #1,wherein the mosaic HA #1 comprises a first HA ectodomain of a first influenza B virus HA, wherein the first HA ectodomain comprises (A) an HA stalk domain of the first influenza B virus HA, and (B) an HA globular head domain of the first influenza B virus HA with amino acid substitutions in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain, and 0, 1, 2, or 3 compensatory amino acid substitutions outside of the 120 loop, the 150 loop, the 160 loop, and the 190 helix, and wherein:(i) the amino acid substitutions in the 120 loop consist of 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the 120 loop of the HA globular head domain of the first influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of a first influenza A virus HA;(ii) the amino acid substitutions in the 150 loop consist of 2, 3, 4, 5, 6, or 7 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the 150 loop of the HA globular head domain of the first influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the first influenza A virus HA;(iii) the amino acid substitutions in the 160 loop consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 160 loop of the HA globular head domain of the first influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the first influenza A virus HA; and(iv) the amino acid substitutions in the 190 helix consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 190 helix of the HA globular head domain of the first influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the first influenza A virus HA; and b) a certain period of time after administration of the first immunogenic composition to the subject, administering to the subject a second immunogenic composition comprising inactivated split influenza B virus #2, a CpG oligonucleotide adjuvant, and an aluminum salt, wherein inactivated split influenza B virus #2 comprises mosaic HA #2, wherein the mosaic HA #2 comprises a second HA ectodomain of a second influenza B virus HA, wherein the second HA ectodomain comprises (A) an HA stalk domain of the second influenza B virus HA, and (B) an HA globular head domain of the second influenza B virus HA with amino acid substitutions in the 120 loop, 150 loop, 160 loop, and 190 helix of theHA globular head domain, and 0, 1, 2, or 3 compensatory amino acid substitutions outside of the 120 loop, the 150 loop, the 160 loop, and the 190 helix, and wherein:(i) the amino acid substitutions in the 120 loop consist of 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the 120 loop of the HA globular head domain of the second influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of a second influenza A virus HA;(ii) the amino acid substitutions in the 150 loop consist of 2, 3, 4, 5, 6, or 7 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the 150 loop of the HA globular head domain of the second influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the second influenza A virus HA;(iii) the amino acid substitutions in the 160 loop consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 160 loop of the HA globular head domain of the second influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the second influenza A virus HA; and(iv) the amino acid substitutions in the 190 helix consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 190 helix of the HA globular head domain of the second influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the second influenza A virus HA, and wherein the first HA ectodomain and the second HA ectodomain comprise different amino acid sequences, and wherein each CpG oligonucleotide adjuvant comprises an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84).

45. A method of inducing a cross-reactive immune response to at least two influenza B viruses in a subject, comprising: a) administering to the subject a first immunogenic composition comprising inactivated split influenza B virus #1, a CpG oligonucleotide adjuvant, and an aluminum salt, wherein inactivated split influenza B virus #1 comprises mosaic hemagglutinin (HA) #1,wherein the mosaic HA #1 comprises a first HA ectodomain of a first influenza B virus HA, wherein the first HA ectodomain comprises (A) an HA stalk domain of the first influenza B virus HA, and (B) an HA globular head domain of the first influenza B virus HA with amino acid substitutions in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain, and 0, 1, 2, or 3 compensatory amino acid substitutions outside of the 120 loop, the 150 loop, the 160 loop, and the 190 helix, and wherein:(i) the amino acid substitutions in the 120 loop consist of 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the 120 loop of the HA globular head domain of the first influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of a first influenza A virus HA;(ii) the amino acid substitutions in the 150 loop consist of 2, 3, 4, 5, 6, or 7 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the 150 loop of the HA globular head domain of the first influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the first influenza A virus HA;(iii) the amino acid substitutions in the 160 loop consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 160 loop of the HA globular head domain of the first influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the first influenza A virus HA; and(iv) the amino acid substitutions in the 190 helix consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 190 helix of the HA globular head domain of the first influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the first influenza A virus HA; and b) a certain period of time after administration of the first immunogenic composition to the subject, administering to the subject a second immunogenic composition comprising inactivated split influenza B virus #2, a CpG oligonucleotide adjuvant, and an aluminum salt, wherein inactivated split influenza B virus #2 comprises mosaic HA #2, wherein the mosaic HA #2 comprises a second HA ectodomain of a second influenza B virus HA, wherein the second HA ectodomain comprises (A) an HA stalk domain of the second influenza B virus HA, and (B) an HA globular head domain of the second influenza B virus HA with amino acid substitutions in the 120 loop, 150 loop, 160 loop, and 190 helix of theHA globular head domain, and 0, 1, 2, or 3 compensatory amino acid substitutions outside of the 120 loop, the 150 loop, the 160 loop, and the 190 helix, and wherein:(i) the amino acid substitutions in the 120 loop consist of 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the 120 loop of the HA globular head domain of the second influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of a second influenza A virus HA;(ii) the amino acid substitutions in the 150 loop consist of 2, 3, 4, 5, 6, or 7 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the 150 loop of the HA globular head domain of the second influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the second influenza A virus HA;(iii) the amino acid substitutions in the 160 loop consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 160 loop of the HA globular head domain of the second influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the second influenza A virus HA; and(iv) the amino acid substitutions in the 190 helix consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 190 helix of the HA globular head domain of the second influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the second influenza A virus HA, and wherein the first HA ectodomain and the second HA ectodomain comprise different amino acid sequences, and wherein each CpG oligonucleotide adjuvant comprises an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84).

46. The method according to any one of claims 43 to 45, wherein the method further comprises administering to the subject a third immunogenic composition a certain time after the administration of the second immunogenic composition to the subject, wherein the third immunogenic composition comprises inactivated split influenza virus #3, a CpG oligonucleotide adjuvant, and an aluminum salt, wherein the inactivated split influenza virus #3 comprises mosaic HA #3, wherein the mosaic HA #3 comprises a third HA ectodomain ofa third influenza B virus HA, wherein the third HA ectodomain comprises (A) an HA stalk domain of the third influenza B virus HA, and (B) an HA globular head domain of the third influenza B virus HA with amino acid substitutions in the 120 loop, 150 loop, 160 loop, and 190 helix, and 0, 1, 2, or 3 compensatory amino acid substitutions outside of the 120 loop, the 150 loop, the 160 loop, and the 190 helix, and wherein:(i) the amino acid substitutions in the 120 loop consist of 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the 120 loop of the HA globular head domain of the third influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of a third influenza A virus HA;(ii) the amino acid substitutions in the 150 loop consist of 2, 3, 4, 5, 6, or 7 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the 150 loop of the HA globular head domain of the third influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the third influenza A virus HA;(iii) the amino acid substitutions in the 160 loop consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 160 loop of the HA globular head domain of the third influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the third influenza A virus HA; and(iv) the amino acid substitutions in the 190 helix consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 190 helix of the HA globular head domain of the third influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the third influenza A virus HA, and wherein the first HA ectodomain, the second HA ectodomain, and the third HA ectodomain each comprise different amino acid sequences, and wherein each CpG oligonucleotide adjuvant comprises an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84).

47. The method according to claim 42, wherein the inactivated influenza B virus #3 isB / Phuket / 3073 / 2013 or B / Brisbane / 60 / 2008.

48. The method according to claim 46, wherein inactivated split influenza B virus #3 is B / Phuket / 3073 / 2013 or B / Brisbane / 60 / 2008.

49. The method according to claim 42, 46, 47, or 48, wherein the third influenza B virus HA ectodomain is the ectodomain of influenza virus B / Phuket / 3073 / 2013 HA or B / Brisbane / 60 / 2008 HA.

50. The method according to any one of claims 42, or 46 to 49, wherein in the mosaic HA #3:(i) the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the amino acid sequence KIP and the amino acid sequence of SEQ ID NO: 21 of the 120 loop of the globular head domain of the third influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the third influenza A virus HA;(ii) the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the amino acid sequence of SEQ ID NO: 22 of the 150 loop of the globular head domain of the third influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the third influenza A virus HA;(iii) the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the amino acid sequence of SEQ ID NO: 23 of the 160 loop of the globular head domain of the third influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the third influenza A virus HA; and(iv) the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the amino acid sequence of SEQ ID NO: 24 of the 190 helix of the globular head domain of the third influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the third influenza A virus HA.

51. The method according to any one of claims 42, or 46 to 49, wherein in the mosaic HA #3:(i) the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the amino acid sequence TTP and the amino acid sequence of SEQ ID NO: 29 of the 120 loop of the globular head domain of the third influenza B virus HAwith amino acid residues found in a corresponding region of the globular head domain of the third influenza A virus HA;(ii) the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the amino acid sequence of SEQ ID NO: 30 of the 150 loop of the globular head domain of the third influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the third influenza A virus HA;(iii) the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the amino acid sequence of SEQ ID NO: 31 of the 160 loop of the globular head domain of the third influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the third influenza A virus HA; and(iv) the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the amino acid sequence of SEQ ID NO: 32 of the 190 helix of the globular head domain of the third influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the third influenza A virus HA.

52. The method according to claim 42, or 46 to 51, wherein the third influenza A virus HA is an exotic avian influenza A virus HA to which humans are naive.

53. The method of according to any one of claims 42, or 46 to 52, wherein the third influenza A virus is an influenza A virus H5, H8, Hl 1, or Hl 3 subtype.

54. The method according to any one of claims 42, or 46 to 53, wherein the third influenza A virus HA is influenza virus A / Vietnam / 1203 / 2004 HA, influenza virus A / mallard / Sweden / 24 / 2002 HA, influenza virus A / shoveler / Netherlands / 18 / 99 HA, or influenza virus A / black-headed gull / / Sweden / l / 1999 HA.

55. The method according to any one of claims 42, or 46 to 49, wherein in the mosaic HA #3:(i) the amino acid sequence TTP and the amino acid sequence of SEQ ID NO: 29 of the 120 loop of the globular head domain of the third influenza B virus HA are substituted with the amino acid sequence FTP and the amino acid sequence of SEQ ID NO: 33, respectively;(ii) the amino acid sequence of SEQ ID NO: 30 of the 150 loop of the globular head domain of the third influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 34;(iii) the amino acid sequence of SEQ ID NO: 31 of the 160 loop of the globular head domain of the third influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 35; and(iv) the amino acid sequence of SEQ ID NO: 32 of the 190 helix of the globular head domain of the third influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 36.

56. The method according to any one of claims 42, or 46 to 49, wherein in the mosaic HA #3:(i) the amino acid sequence KIP and the amino acid sequence of SEQ ID NO: 21 of the 120 loop of the globular head domain of the third influenza B virus HA are substituted with the amino acid sequence NIP and the amino acid sequence of SEQ ID NO: 25, respectively;(ii) the amino acid sequence of SEQ ID NO: 22 of the 150 loop of the globular head domain of the third influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 26;(iii) the amino acid sequence of SEQ ID NO: 23 of the 160 loop of the globular head domain of the third influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 27; and(iv) the amino acid sequence of SEQ ID NO: 24 of the 190 helix of the globular head domain of the third influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 28 or 37.

57. The method according to any one of claims 43 to 46, or 48 to 56, wherein the inactivated split influenza B virus #1 is B / Yamagata / 16 / 1988.

58. The method according to any one of claims 39 to 42, 47, or 49 to 56, wherein the inactivated influenza B virus #1 is B / Yamagata / 16 / 1988.

59. The method according to any one of claims 39 to 58, wherein the first influenza B virus HA ectodomain is the ectodomain of influenza virus B / Yamagata / 16 / 1988 HA.

60. The method according to claim 39 to 59, wherein in the mosaic HA #1 :(i) the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the amino acid sequence TIP and the amino acid sequence of SEQ ID NO: 1 of the 120 loop of the globular head domain of the first influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the first influenza A virus HA;(ii) the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the amino acid sequence of SEQ ID NO: 2 of the 150 loop of the globular head domain of the first influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the third influenza A virus HA;(iii) the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the amino acid sequence of SEQ ID NO: 3 of the 160 loop of the globular head domain of the first influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the first influenza A virus HA; and(iv) the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the amino acid sequence of SEQ ID NO: 4 of the 190 helix of the globular head domain of the first influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the first influenza A virus HA.

61. The method according to claim 39 to 60, wherein the first influenza A virus HA is an exotic avian influenza A virus HA to which humans are naive.

62. The method of according to any one of claims 39 to 61, wherein the first influenza A virus is an influenza A virus H5, H8, Hl 1, or Hl 3 subtype.

63. The method according to claim 39 to 62, wherein the first influenza A virus HA is influenza virus A / Vietnam / 1203 / 2004 HA, influenza virus A / mallard / Sweden / 24 / 2002 HA, influenza virus A / shoveler / Netherlands / 18 / 99 HA, or influenza virus A / black-headed gull / / Sweden / l / 1999 HA.

64. The method according to any one of claims 39 to 63, wherein in the mosaic HA #1 :(A) (i) the amino acid sequence TIP and the amino acid sequence of SEQ ID NO: 1 of the 120 loop of the globular head domain of the first influenza B virus HA are substituted with the amino acid sequence FIP and the amino acid sequence of SEQ ID NO: 5, respectively;(ii) the amino acid sequence of SEQ ID NO: 2 of the 150 loop of the globular head domain of the first influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 6;(iii) the amino acid sequence of SEQ ID NO: 3 of the 160 loop of the globular head domain of the first influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 7; and(iv) the amino acid sequence of SEQ ID NO: 4 of the 190 helix of the globular head domain of the first influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 8; or(B) (i) the amino acid sequence TIP and the amino acid sequence of SEQ ID NO: 1 of the 120 loop of the globular head domain of the first influenza B virus HA are substituted with the amino acid sequence HIP and the amino acid sequence of SEQ ID NO: 9, respectively;(ii) the amino acid sequence of SEQ ID NO: 2 of the 150 loop of the globular head domain of the first influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 10;(iii) the amino acid sequence of SEQ ID NO: 3 of the 160 loop of the globular head domain of the first influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 11; and(iv) the amino acid sequence of SEQ ID NO: 4 of the 190 helix of the globular head domain of the first influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 12; or(C) (i) the amino acid sequence TIP and the amino acid sequence of SEQ ID NO: 1 of the 120 loop of the globular head domain of the first influenza B virus HA are substituted with the amino acid sequence LIP and the amino acid sequence of SEQ ID NO: 13, respectively;(ii) the amino acid sequence of SEQ ID NO: 2 of the 150 loop of the globular head domain of the first influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 14;(iii) the amino acid sequence of SEQ ID NO: 3 of the 160 loop of the globular head domain of the first influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 15; and(iv) the amino acid sequence of SEQ ID NO: 4 of the 190 helix of the globular head domain of the first influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 16; or(D) (i) the amino acid sequence TIP and the amino acid sequence of SEQ IDNO: 1 of the 120 loop of the globular head domain of the first influenza B virus HA are substituted with the amino acid sequence NIP and the amino acid sequence of SEQ ID NO: 17, respectively;(ii) the amino acid sequence of SEQ ID NO: 2 of the 150 loop of the globular head domain of the first influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 18;(iii) the amino acid sequence of SEQ ID NO: 3 of the 160 loop of the globular head domain of the first influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 19; and(iv) the amino acid sequence of SEQ ID NO: 4 of the 190 helix of the globular head domain of the first influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 20.

65. The method according to any one of claims 43 to 46, 48 to 57, or 59 to 64, wherein the inactivated influenza B virus #2 is B / Phuket / 3073 / 2013 or B / Brisbane / 60 / 2008.

66. The method according to any one of claims 39 to 42, 47, 49 to 56, or 58 to 64, wherein inactivated split influenza B virus #2 is B / Phuket / 3073 / 2013 or B / Brisbane / 60 / 2008.

67. The method according to claim 39 to 66, wherein the second influenza B virus HA ectodomain is the ectodomain of influenza virus B / Phuket / 3073 / 2013 HA or B / Brisbane / 60 / 2008 HA.

68. The method according to any one of claims 39 to 67, wherein in the mosaic HA #2: (i) the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the amino acid sequence KIP and the amino acid sequence of SEQ ID NO:21 of the 120 loop of the globular head domain of the second influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the second influenza A virus HA;(ii) the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the amino acid sequence of SEQ ID NO: 22 of the 150 loop of the globular head domain of the second influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the second influenza A virus HA;(iii) the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the amino acid sequence of SEQ ID NO: 23 of the 160 loop of the globular head domain of the second influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the second influenza A virus HA; and(iv) the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the amino acid sequence of SEQ ID NO: 24 of the 190 helix of the globular head domain of the second influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the second influenza A virus HA.

69. The method according to any one of claims 39 to 67, wherein in the mosaic HA #2:(i) the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the amino acid sequence TTP and the amino acid sequence of SEQ ID NO: 29 of the 120 loop of the globular head domain of the second influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the second influenza A virus HA;(ii) the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the amino acid sequence of SEQ ID NO: 30 of the 150 loop of the globular head domain of the second influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the second influenza A virus HA;(iii) the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the amino acid sequence of SEQ ID NO: 31 of the 160 loop of the globular head domain of the second influenza B virus HA with amino acid residues found in acorresponding region of the globular head domain of the second influenza A virus HA; and(iv) the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the amino acid sequence of SEQ ID NO: 32 of the 190 helix of the globular head domain of the second influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the second influenza A virus HA.

70. The method according to claim 39 to 69, wherein the second influenza A virus HA is an exotic avian influenza A virus HA to which humans are naive.

71. The method of according to any one of claims 39 to 70, wherein the second influenza A virus is an influenza A virus H5, H8, Hl 1, or Hl 3 subtype.

72. The method according to any one of claims 39 to 71, wherein the second influenza A virus HA is influenza virus A / Vietnam / 1203 / 2004 HA, influenza virus A / mallard / Sweden / 24 / 2002 HA, influenza virus A / shoveler / Netherlands / 18 / 99 HA, or influenza virus A / black-headed gull / / Sweden / l / 1999 HA.

73. The method according to any one of claims 39 to 72, wherein in mosaic HA #2:(i) the amino acid sequence TTP and the amino acid sequence of SEQ ID NO: 29 of the 120 loop of the globular head domain of the second influenza B virus HA are substituted with the amino acid sequence FTP and the amino acid sequence of SEQ ID NO: 33, respectively;(ii) the amino acid sequence of SEQ ID NO: 30 of the 150 loop of the globular head domain of the second influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 34;(iii) the amino acid sequence of SEQ ID NO: 31 of the 160 loop of the globular head domain of the second influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 35; and(iv) the amino acid sequence of SEQ ID NO: 32 of the 190 helix of the globular head domain of the second influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 36.

74. The method according to any one of claims 39 to 72, wherein:(i) the amino acid sequence KIP and the amino acid sequence of SEQ ID NO: 21 of the 120 loop of the globular head domain of the second influenza B virus HA are substituted with the amino acid sequence NIP and the amino acid sequence of SEQ ID NO: 25, respectively;(ii) the amino acid sequence of SEQ ID NO: 22 of the 150 loop of the globular head domain of the second influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 26;(iii) the amino acid sequence of SEQ ID NO: 23 of the 160 loop of the globular head domain of the second influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 27; and(iv) the amino acid sequence of SEQ ID NO: 24 of the 190 helix of the globular head domain of the second influenza B virus HA is substituted with the amino acid sequence of SEQ ID NO: 28 or 37.

75. A method of preventing influenza virus disease in a subject, comprising: a) administering to the subject a first immunogenic composition comprising a first inactivated influenza virus, a CpG oligonucleotide adjuvant, and aluminum salt, wherein the first inactivated influenza virus comprises a first mosaic HA, and wherein the first mosaic HA comprises the amino acid sequence of SEQ ID NO: 38, 40, 42, 44, 46, or 48; and b) a certain period of time after administration of the first immunogenic composition to the subject, administering to the subject a second immunogenic composition comprising a second inactivated influenza virus, a CpG oligonucleotide adjuvant, and aluminum salt, wherein the second inactivated influenza virus comprises a second mosaic HA, and wherein the second mosaic HA comprises the amino acid sequence of SEQ ID NO: 38, 40, 42, 44, 46, or 48, wherein the first mosaic HA and the second mosaic HA comprise different amino acid sequences, and wherein each CpG oligonucleotide adjuvant comprises an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84).

76. A method of immunizing a subject against influenza virus disease, comprising: a) administering to the subject a first immunogenic composition comprising a first inactivated influenza virus, a CpG oligonucleotide adjuvant, and aluminum salt, whereinthe first inactivated influenza virus comprises a first mosaic HA, and wherein the first mosaic HA comprises the amino acid sequence of SEQ ID NO: 38, 40, 42, 44, 46, or 48; and b) a certain period of time after administration of the first immunogenic composition to the subject, administering to the subject a second immunogenic composition comprising a second inactivated influenza virus, a CpG oligonucleotide adjuvant, and aluminum salt, wherein the second inactivated influenza virus comprises a second mosaic HA, and wherein the second mosaic HA comprises the amino acid sequence of SEQ ID NO: 38, 40, 42, 44, 46, or 48, wherein the first mosaic HA and the second mosaic HA comprise different amino acid sequences, and wherein each CpG oligonucleotide adjuvant comprises an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84).

77. A method of inducing a cross-reactive immune response to at least two influenza B viruses in a subject, comprising: a) administering to the subject a first immunogenic composition comprising a first inactivated influenza virus, a CpG oligonucleotide adjuvant, and aluminum salt, wherein the first inactivated influenza virus comprises a first mosaic HA, and wherein the first mosaic HA comprises the amino acid sequence of SEQ ID NO: 38, 40, 42, 44, 46, or 48; and b) a certain period of time after administration of the first immunogenic composition to the subject, administering to the subject a second immunogenic composition comprising a second inactivated influenza virus, a CpG oligonucleotide adjuvant, and aluminum salt, wherein the second inactivated influenza virus comprises a second mosaic HA, and wherein the second mosaic HA comprises the amino acid sequence of SEQ ID NO: 38, 40, 42, 44, 46, or 48, wherein the first mosaic HA and the second mosaic HA comprise different amino acid sequences, and wherein each CpG oligonucleotide adjuvant comprises an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84).

78. A method of preventing influenza virus disease in a subject, comprising: a) administering to the subject a first immunogenic composition comprising a first inactivated split influenza virus, a CpG oligonucleotide adjuvant, and aluminum salt,wherein the first inactivated split influenza virus comprises a first mosaic HA, and wherein the first mosaic HA comprises the amino acid sequence of SEQ ID NO: 38, 40, 42, 44, 46, or 48; and b) a certain period of time after administration of the first immunogenic composition to the subject, administering to the subject a second immunogenic composition comprising a second split inactivated influenza virus, a CpG oligonucleotide adjuvant, and aluminum salt, wherein the second inactivated split influenza virus comprises a second mosaic HA, and wherein the second mosaic HA comprises the amino acid sequence of SEQ ID NO: 38, 40, 42, 44, 46, or 48, wherein the first mosaic HA and the second mosaic HA comprise different amino acid sequences, and wherein each CpG oligonucleotide adjuvant comprises an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84).

79. A method of immunizing a subject against influenza virus disease, comprising: a) administering to the subject a first immunogenic composition comprising a first inactivated split influenza virus, a CpG oligonucleotide adjuvant, and aluminum salt, wherein the first inactivated split influenza virus comprises a first mosaic HA, and wherein the first mosaic HA comprises the amino acid sequence of SEQ ID NO: 38, 40, 42, 44, 46, or 48; and b) a certain period of time after administration of the first immunogenic composition to the subject, administering to the subject a second immunogenic composition comprising a second split inactivated influenza virus, a CpG oligonucleotide adjuvant, and aluminum salt, wherein the second inactivated split influenza virus comprises a second mosaic HA, and wherein the second mosaic HA comprises the amino acid sequence of SEQ ID NO: 38, 40, 42, 44, 46, or 48, wherein the first mosaic HA and the second mosaic HA comprise different amino acid sequences, and wherein each CpG oligonucleotide adjuvant comprises an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84).

80. A method of inducing a cross-reactive immune response to at least two influenza B viruses in a subject, comprising:a) administering to the subject a first immunogenic composition comprising a first inactivated split influenza virus, a CpG oligonucleotide adjuvant, and aluminum salt, wherein the first inactivated split influenza virus comprises a first mosaic HA, and wherein the first mosaic HA comprises the amino acid sequence of SEQ ID NO: 38, 40, 42, 44, 46, or 48; and b) a certain period of time after administration of the first immunogenic composition to the subject, administering to the subject a second immunogenic composition comprising a second inactivated split influenza virus, a CpG oligonucleotide adjuvant, and aluminum salt, wherein the second inactivated split influenza virus comprises a second mosaic HA, and wherein the second mosaic HA comprises the amino acid sequence of SEQ ID NO: 38, 40, 42, 44, 46, or 48, wherein the first mosaic HA and the second mosaic HA comprise different amino acid sequences, and wherein each CpG oligonucleotide adjuvant comprises an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84).

81. The method according to any one of claims 39 to 80, wherein the second immunogenic composition is administered to the subject about 21 to about 6 months after the administration of the first immunogenic composition to the subject.

82. The method according to any one of claims 39 to 81, wherein the oligonucleotide comprises the nucleotide sequence of 5’-TGACTGTGAACGTTCGAGATGA-3’ (SEQ ID NO: 85).

83. The method according to any one according to claims 39 to 82, wherein the oligonucleotide is 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, or 35 nucleotides in length.

84. The method according to any one of claims 39 to 83, wherein the oligonucleotide is a single stranded oligodeoxynucleotide.

85. The method according to any one of claims 39 to 83, wherein the oligonucleotide is fully RNA or is an RNA / DNA chimera.

86. The method according to any one of claims 39 to 85, wherein the oligonucleotide comprises only phosphorothioate linkages, or a combination of one or more phosphodiester linkages and one or more phosphorothioate linkages.

87. The method according to any one of claims 39 to 86, wherein the aluminum salt comprises one or more selected from the group consisting of amorphous aluminum hydroxyphosphate sulfate, aluminum hydroxide, aluminum phosphate, and potassium aluminum sulfate.

88. The method according to any one of claims 39 to 86, wherein the aluminum salt comprises aluminum hydroxide or aluminum phosphate.

89. The method according to any one of claims 39 to 88, wherein the first immunogenic composition or second immunogenic is administered to the subject intramuscularly or intranasally.

90. The method according to any one of claims 39 to 88, wherein the first immunogenic composition and second immunogenic are administered to the subject intramuscularly or intranasally.

91. The method according to any one of claims 35 to 90, wherein the subject is human.

92. A method of preventing an influenza virus disease in a subject, comprising: a) administering to the subject an immunogenic composition comprising a mosaic hemagglutinin (HA), wherein the mosaic HA comprises an HA ectodomain of an influenza B virus HA, wherein the HA ectodomain comprises (A) an HA stalk domain of the influenza B virus HA, and (B) an HA globular head domain of the influenza B virus HA with amino acid substitutions in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain, and 0, 1, 2, or 3 compensatory amino acid substitutions outside of the 120 loop, the 150 loop, the 160 loop, and the 190 helix, wherein:(i) the amino acid substitutions in the 120 loop consist of 2, 3, 4, 5, 6, 7, 8, 9, or10 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the 120 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA;(ii) the amino acid substitutions in the 150 loop consist of 2, 3, 4, 5, 6, or 7 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the 150 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA;(iii) the amino acid substitutions in the 160 loop consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 160 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA; and(iv) the amino acid substitutions in the 190 helix consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 190 helix of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA; b) administering to the subject a CpG oligonucleotide adjuvant comprising an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84); and c) administering to the subject an aluminum salt.

93. A method of immunizing a subject against influenza virus disease, comprising: a) administering to the subject an immunogenic composition comprising a mosaic hemagglutinin (HA), wherein the mosaic HA comprises an HA ectodomain of an influenza B virus HA, wherein the HA ectodomain comprises (A) an HA stalk domain of the influenza B virus HA, and (B) an HA globular head domain of the influenza B virus HA with amino acid substitutions in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain, and 0, 1, 2, or 3 compensatory amino acid substitutions outside of the 120 loop, the 150 loop, the 160 loop, and the 190 helix, wherein:(i) the amino acid substitutions in the 120 loop consist of 2, 3, 4, 5, 6, 7, 8, 9, or10 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the 120 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA;(ii) the amino acid substitutions in the 150 loop consist of 2, 3, 4, 5, 6, or 7 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the 150 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA;(iii) the amino acid substitutions in the 160 loop consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 160 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA; and(iv) the amino acid substitutions in the 190 helix consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 190 helix of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA; b) administering to the subject a CpG oligonucleotide adjuvant comprising an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84); and c) administering to the subject an aluminum salt.

94. A method of inducing a cross-reactive immune response to at least two influenza B viruses in a subject, comprising: a) administering to the subject an immunogenic composition comprising a mosaic hemagglutinin (HA), wherein the mosaic HA comprises an HA ectodomain of an influenza B virus HA, wherein the HA ectodomain comprises (A) an HA stalk domain of the influenza B virus HA, and (B) an HA globular head domain of the influenza B virus HA with amino acid substitutions in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain, and 0, 1, 2, or 3 compensatory amino acid substitutions outside of the 120 loop, the 150 loop, the 160 loop, and the 190 helix, wherein:(i) the amino acid substitutions in the 120 loop consist of 2, 3, 4, 5, 6, 7, 8, 9, or10 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the 120 loop of the globular head domainof the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA;(ii) the amino acid substitutions in the 150 loop consist of 2, 3, 4, 5, 6, or 7 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the 150 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA;(iii) the amino acid substitutions in the 160 loop consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 160 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA; and(iv) the amino acid substitutions in the 190 helix consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 190 helix of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA; b) administering to the subject a CpG oligonucleotide adjuvant comprising an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84); and c) administering to the subject an aluminum salt.

95. A method of preventing an influenza virus disease in a subject, comprising: a) administering to the subject an immunogenic composition comprising an inactivated influenza virus in an admixture with a pharmaceutically acceptable carrier, wherein the inactivated influenza virus comprises a mosaic hemagglutinin (HA), wherein the mosaic HA comprises an HA ectodomain of an influenza B virus HA, wherein the HA ectodomain comprises (A) an HA stalk domain of the influenza B virus HA, and (B) an HA globular head domain of the influenza B virus HA with amino acid substitutions in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain, and 0, 1, 2, or 3 compensatory amino acid substitutions outside of the 120 loop, the 150 loop, the 160 loop, and the 190 helix, wherein:(i) the amino acid substitutions in the 120 loop consist of 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the 120 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA;(ii) the amino acid substitutions in the 150 loop consist of 2, 3, 4, 5, 6, or 7 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the 150 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA;(iii) the amino acid substitutions in the 160 loop consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 160 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA; and(iv) the amino acid substitutions in the 190 helix consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 190 helix of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA; b) administering to the subject a CpG oligonucleotide adjuvant comprising an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84); and c) administering to the subject an aluminum salt.

96. A method of immunizing a subject against influenza virus disease, comprising: a) administering to the subject an immunogenic composition comprising an inactivated influenza virus in an admixture with a pharmaceutically acceptable carrier, wherein the inactivated influenza virus comprises a mosaic hemagglutinin (HA), wherein the mosaic HA comprises an HA ectodomain of an influenza B virus HA, wherein the HA ectodomain comprises (A) an HA stalk domain of the influenza B virus HA, and (B) an HA globular head domain of the influenza B virus HA with amino acid substitutions in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain, and 0, 1, 2, or 3compensatory amino acid substitutions outside of the 120 loop, the 150 loop, the 160 loop, and the 190 helix, wherein:(i) the amino acid substitutions in the 120 loop consist of 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the 120 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA;(ii) the amino acid substitutions in the 150 loop consist of 2, 3, 4, 5, 6, or 7 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the 150 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA;(iii) the amino acid substitutions in the 160 loop consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 160 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA; and(iv) the amino acid substitutions in the 190 helix consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 190 helix of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA; b) administering to the subject a CpG oligonucleotide adjuvant comprising an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84); and c) administering to the subject an aluminum salt.

97. A method of inducing a cross-reactive immune response to at least two influenza B viruses in a subject, comprising: a) administering to the subject an immunogenic composition comprising an inactivated influenza virus in an admixture with a pharmaceutically acceptable carrier, wherein the inactivated influenza virus comprises a mosaic hemagglutinin (HA), wherein the mosaic HA comprises an HA ectodomain of an influenza B virus HA, wherein the HAectodomain comprises (A) an HA stalk domain of the influenza B virus HA, and (B) an HA globular head domain of the influenza B virus HA with amino acid substitutions in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain, and 0, 1, 2, or 3 compensatory amino acid substitutions outside of the 120 loop, the 150 loop, the 160 loop, and the 190 helix, wherein:(i) the amino acid substitutions in the 120 loop consist of 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the 120 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA;(ii) the amino acid substitutions in the 150 loop consist of 2, 3, 4, 5, 6, or 7 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the 150 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA;(iii) the amino acid substitutions in the 160 loop consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 160 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA; and(iv) the amino acid substitutions in the 190 helix consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 190 helix of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA; b) administering to the subject a CpG oligonucleotide adjuvant comprising an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84); and c) administering to the subject an aluminum salt.

98. A method of preventing an influenza virus disease in a subject, comprising: a) administering to the subject an immunogenic composition comprising an inactivated split influenza virus in an admixture with a pharmaceutically acceptable carrier,wherein the inactivated split influenza virus comprises a mosaic hemagglutinin (HA), wherein the mosaic HA comprises an HA ectodomain of an influenza B virus HA, wherein the HA ectodomain comprises (A) an HA stalk domain of the influenza B virus HA, and (B) an HA globular head domain of the influenza B virus HA with amino acid substitutions in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain, and 0, 1, 2, or 3 compensatory amino acid substitutions outside of the 120 loop, the 150 loop, the 160 loop, and the 190 helix, wherein:(i) the amino acid substitutions in the 120 loop consist of 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the 120 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA;(ii) the amino acid substitutions in the 150 loop consist of 2, 3, 4, 5, 6, or 7 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the 150 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA;(iii) the amino acid substitutions in the 160 loop consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 160 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA; and(iv) the amino acid substitutions in the 190 helix consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 190 helix of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA; b) administering to the subject a CpG oligonucleotide adjuvant comprising an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84); and c) administering to the subject an aluminum salt.

99. A method of immunizing a subject against influenza virus disease, comprising:a) administering to the subject an immunogenic composition comprising an inactivated split influenza virus in an admixture with a pharmaceutically acceptable carrier, wherein the inactivated split influenza virus comprises a mosaic hemagglutinin (HA), wherein the mosaic HA comprises an HA ectodomain of an influenza B virus HA, wherein the HA ectodomain comprises (A) an HA stalk domain of the influenza B virus HA, and (B) an HA globular head domain of the influenza B virus HA with amino acid substitutions in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain, and 0, 1, 2, or 3 compensatory amino acid substitutions outside of the 120 loop, the 150 loop, the 160 loop, and the 190 helix, wherein:(i) the amino acid substitutions in the 120 loop consist of 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the 120 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA;(ii) the amino acid substitutions in the 150 loop consist of 2, 3, 4, 5, 6, or 7 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the 150 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA;(iii) the amino acid substitutions in the 160 loop consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 160 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA; and(iv) the amino acid substitutions in the 190 helix consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 190 helix of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA; b) administering to the subject a CpG oligonucleotide adjuvant, wherein the CpG oligonucleotide adjuvant comprises an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84); and c) administering to the subject an aluminum salt.

100. A method of inducing a cross-reactive immune response to at least two influenza B viruses in a subject, comprising: a) administering to the subject an immunogenic composition comprising an inactivated split influenza virus in an admixture with a pharmaceutically acceptable carrier, wherein the inactivated split influenza virus comprises a mosaic hemagglutinin (HA), wherein the mosaic HA comprises an HA ectodomain of an influenza B virus HA, wherein the HA ectodomain comprises (A) an HA stalk domain of the influenza B virus HA, and (B) an HA globular head domain of the influenza B virus HA with amino acid substitutions in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain, and 0, 1, 2, or 3 compensatory amino acid substitutions outside of the 120 loop, the 150 loop, the 160 loop, and the 190 helix, wherein:(i) the amino acid substitutions in the 120 loop consist of 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the 120 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA;(ii) the amino acid substitutions in the 150 loop consist of 2, 3, 4, 5, 6, or 7 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the 150 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA;(iii) the amino acid substitutions in the 160 loop consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 160 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA; and(iv) the amino acid substitutions in the 190 helix consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 190 helix of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA;b) administering to the subject a CpG oligonucleotide adjuvant comprising an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84); and c) administering to the subject an aluminum salt.

101. The method according to any one of claims 92 to 100, wherein the influenza B virus is B / Yamagata / 16 / 1988, B / Phuket / 3073 / 2013, or B / Brisbane / 60 / 2008.

102. The method according to any one of claims 92 to 101, wherein the influenza B virus HA ectodomain is the ectodomain of influenza virus B / Yamagata / 16 / 1988 HA, B / Phuket / 3073 / 2013 HA, or B / Brisbane / 60 / 2008 HA.

103. The method according to any one of claims 92 to 102, wherein the influenza A virus HA is an exotic avian influenza A virus HA to which humans are naive.

104. The method of according to any one of claims 92 to 103, wherein the influenza A virus is an influenza A virus H5, H8, Hl 1, or Hl 3 subtype.

105. The method according to any one of claims 92 to 104, wherein the influenza A virus HA is influenza virus A / Vietnam / 1203 / 2004 HA, influenza virus A / mallard / Sweden / 24 / 2002 HA, influenza virus A / shoveler / Netherlands / 18 / 99 HA, or influenza virus A / black-headed gull / / Sweden / l / 1999 HA.

106. A method of preventing an influenza virus disease in a subject, comprising: a) administering to the subject an immunogenic composition comprising an inactivated influenza virus or inactivated split influenza virus in an admixture with a pharmaceutically acceptable carrier, wherein the inactivated influenza virus or the inactivated split influenza virus comprises a mosaic hemagglutinin (HA), wherein the mosaic HA comprises the amino acid sequence of SEQ ID NO: 38, 40, 42, 44, 46, or 48; b) administering to the subject a CpG oligonucleotide adjuvant comprising an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84); and c) administering to the subject an aluminum salt.

107. A method of immunizing a subject against influenza virus disease, comprising: a) administering to the subject an immunogenic composition comprising an inactivated influenza virus or inactivated split influenza virus in an admixture with a pharmaceutically acceptable carrier, wherein the inactivated influenza virus or the inactivated split influenza virus comprises a mosaic hemagglutinin (HA), wherein the mosaic HA comprises the amino acid sequence of SEQ ID NO: 38, 40, 42, 44, 46, or 48; b) administering to the subject a CpG oligonucleotide adjuvant comprising an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84); and c) administering to the subject an aluminum salt.

108. A method of inducing a cross-reactive immune response to at least two influenza B viruses in a subject, comprising: a) administering to the subject an immunogenic composition comprising an inactivated influenza virus or inactivated split influenza virus in an admixture with a pharmaceutically acceptable carrier, wherein the inactivated influenza virus or the inactivated split influenza virus comprises a mosaic hemagglutinin (HA), wherein the mosaic HA comprises the amino acid sequence of SEQ ID NO: 38, 40, 42, 44, 46, or 48; b) administering to the subject a CpG oligonucleotide adjuvant comprising an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84); and c) administering to the subject an aluminum salt.

109. The method according to any one of claims 92 to 108, wherein the oligonucleotide comprises the nucleotide sequence of 5’-TGACTGTGAACGTTCGAGATGA-3’(SEQ ID NO: 85).

110. The method according to any one of claims 92 to 109, wherein the oligonucleotide is 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, or 35 nucleotides in length.

111. The method according to any one of claims 92 to 110, wherein the oligonucleotide is a single stranded oligodeoxynucleotide.

112. The method according to any one of claims 92 to 110, wherein the oligonucleotide is fully RNA or is an RNA / DNA chimera.

113. The method according to any one of claims 92 to 112, wherein the oligonucleotide comprises only phosphorothioate linkages, or a combination of one or more phosphodiester linkages and one or more phosphorothioate linkages.

114. The method according to any one of method 92 to 113, wherein the immunogenic composition, the CpG oligonucleotide adjuvant, the aluminum salt, or all three are administered intramuscularly to the subject.

115. The method according to any one of claims 92 to 114, wherein the aluminum salt comprises one or more selected from the group consisting of amorphous aluminum hydroxyphosphate sulfate, aluminum hydroxide, aluminum phosphate, and potassium aluminum sulfate.

116. The method according to any one of claims 92 to 114, wherein the aluminum salt comprises aluminum hydroxide or aluminum phosphate.

117. The method according to any one of claims 92 to 116, wherein the subject is human.

118. The method according to any one of claims 92 to 117, wherein the immunogenic composition, the CpG oligonucleotide adjuvant, and the aluminum salt are administered concurrently to the subject.

119. The method according to any one of claims 92 to 117, wherein the immunogenic composition, the CpG oligonucleotide adjuvant, and the aluminum salt are administered to the subject within 30 minutes of each other.

120. The method according to any one of claims 92 to 117, wherein the immunogenic composition, the CpG oligonucleotide adjuvant, and the aluminum salt are administered to the subject within 15 minutes of each other.

121. A kit comprising a container containing the immunogenic composition of any one of claims 1 to 34.

122. A kit compri sing : a) a first container containing an immunogenic composition comprising a mosaic HA, wherein the mosaic HA comprises an HA ectodomain of an influenza B virus HA, wherein the HA ectodomain comprises (A) an HA stalk domain of the influenza B virus HA, and (B) an HA globular head domain of the influenza B virus HA with amino acid substitutions in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain, and 0, 1, 2, or 3 compensatory amino acid substitutions outside of the 120 loop, the 150 loop, the 160 loop, and the 190 helix, wherein:(i) the amino acid substitutions in the 120 loop consist of 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the 120 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA;(ii) the amino acid substitutions in the 150 loop consist of 2, 3, 4, 5, 6, or 7 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the 150 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA;(iii) the amino acid substitutions in the 160 loop consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 160 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA; and(iv) the amino acid substitutions in the 190 helix consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 190 helix of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA; and b) a second container containing a CpG oligonucleotide adjuvant comprising an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84).

123. A kit compri sing :a) a first container containing an immunogenic composition comprising an inactivated influenza virus or inactivated split influenza virus, wherein the inactivated influenza virus or inactivated split influenza virus comprises a mosaic HA, wherein the mosaic HA comprises an HA ectodomain of an influenza B virus HA, wherein the HA ectodomain comprises (A) an HA stalk domain of the influenza B virus HA, and (B) an HA globular head domain of the influenza B virus HA with amino acid substitutions in the 120 loop, 150 loop, 160 loop, and 190 helix of the HA globular head domain, and 0, 1, 2, or 3 compensatory amino acid substitutions outside of the 120 loop, the 150 loop, the 160 loop, and the 190 helix, wherein:(i) the amino acid substitutions in the 120 loop consist of 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues in the 120 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of an influenza A virus HA;(ii) the amino acid substitutions in the 150 loop consist of 2, 3, 4, 5, 6, or 7 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, 6, or 7 amino acid residues in the 150 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA;(iii) the amino acid substitutions in the 160 loop consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 160 loop of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA; and(iv) the amino acid substitutions in the 190 helix consist of 2, 3, 4, 5, or 6 amino acid substitutions, and wherein the amino acid substitutions substitute 2, 3, 4, 5, or 6 amino acid residues in the 190 helix of the globular head domain of the influenza B virus HA with amino acid residues found in a corresponding region of the globular head domain of the influenza A virus HA; and b) a second container containing a CpG oligonucleotide adjuvant comprising an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84).

124. A kit compri sing :(a) a first container containing a first immunogenic composition comprising a first inactivated influenza virus or a first inactivated split influenza virus and a CpG oligonucleotide adjuvant, wherein the first inactivated influenza virus or the first inactivated split influenza virus comprises a first mosaic HA, wherein the first mosaic HA comprises the amino acid sequence of SEQ ID NO: 38, 40, 42, 44, 46, or 48; and(b) a second container containing a second immunogenic composition comprising a second inactivated influenza virus or a second inactivated split influenza virus and a CpG oligonucleotide adjuvant, wherein the second inactivated influenza virus or the second inactivated split influenza virus comprises a second mosaic HA, wherein the second mosaic HA comprises the amino acid sequence of SEQ ID NO: 38, 40, 42, 44, 46, or 48, wherein the first mosaic HA and second mosaic HA comprise different amino acid sequences, and wherein each CpG oligonucleotide adjuvant comprises an oligonucleotide of from 10 to 35 nucleotides in length comprising the nucleotide sequence of 5’-GAACGTTCG-3’ (SEQ ID NO: 84).

125. The kit according to any one of claims 122 to 124, wherein the oligonucleotide comprises the nucleotide sequence of 5’-TGACTGTGAACGTTCGAGATGA-3’ (SEQ ID NO: 85).

126. The kit according to any one of claims 122 to 125, wherein the kit further comprises a third container comprising an aluminum salt.

127. The kit according to claim 126, wherein the aluminum salt comprises one or more selected from the group consisting of amorphous aluminum hydroxyphosphate sulfate, aluminum hydroxide, aluminum phosphate, and potassium aluminum sulfate.

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