Recombinant Newcastle Disease Viruses and Immunogenic Compositions for Use in the Prevention of COVID-19

Abstract

Described herein is a recombinant Newcastle Disease Virus ("NDV") comprising a packaged genome, the packaged genome comprising a transgene comprising a nucleotide sequence encoding a protein comprising the spike protein of SARS-CoV-2 or a portion thereof. Also described herein is a recombinant NDV comprising a packaged genome, the packaged genome comprising a transgene encoding a chimeric F protein, the chimeric F protein comprising the extracellular domain of the spike protein of SARS-CoV-2 and the transmembrane and cytoplasmic domains of the NDV F protein. Also described herein is an immunogenic composition comprising the recombinant NDV. The recombinant NDV and immunogenic composition are useful for immunizing against SARS-CoV-2 and preventing COVID-19.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Patent Application No. 63 / 318,640, filed March 10, 2022, the disclosure of which is incorporated by reference in its entirety herein.

[0002] Statement regarding federally sponsored research This invention was made with Government support under Grant No. HHSN272201400008C awarded by the National Institutes of Health. The Government has certain rights in the invention.

[0003] Sequence Listing This application contains a computer readable sequence listing that has been submitted herewith in XML file format, the entire contents of which are incorporated herein by reference in their entirety. The sequence listing XML file submitted herewith is entitled "06923-384-228_SEQ_LISTING.xml", was created on March 9, 2023, and is 173,741 bytes in size.

[0004] 1. Introduction In one aspect, described herein is a recombinant Newcastle Disease Virus (NDV) comprising a packaged genome, the packaged genome comprising a transgene encoding a protein comprising a spike protein of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), or a portion thereof (e.g., the extracellular domain or receptor binding domain of the SARS-CoV-2 spike protein). In a particular embodiment, described herein is a recombinant NDV comprising a packaged genome, the packaged genome comprising a transgene comprising a codon-optimized nucleic acid sequence encoding a protein comprising a spike protein of SARS-CoV-2, or a portion thereof (e.g., the extracellular domain or receptor binding domain of the SARS-CoV-2 spike protein). In a particular embodiment, described herein is a recombinant NDV comprising a packaged genome, the packaged genome comprising a transgene encoding a chimeric F protein, the chimeric F protein comprising the extracellular domain of the SARS-CoV-2 spike protein, and the transmembrane and cytoplasmic domains of the NDV F protein. In certain embodiments, described herein is a recombinant NDV comprising a packaged genome, the packaged genome comprising a transgene encoding a chimeric F protein, the chimeric F protein comprising a derivative of the extracellular domain of the spike protein of SARS-CoV-2, and the transmembrane and cytoplasmic domains of the NDV F protein. Also described herein are compositions comprising such recombinant NDVs, and the use of the recombinant NDVs and compositions to induce an immune response against the SARS-CoV-2 spike protein, and the use of the recombinant NDVs and compositions in immunoassays to detect the presence of antibodies that bind to the SARS-CoV-2 spike protein. Additionally provided herein are bivalent and multivalent immunogenic compositions comprising the recombinant NDVs, and the use of the immunogenic compositions to immunize against SARS-CoV-2 and prevent COVID-19. [Background technology]

[0005] 2.Background technology Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative pathogen of the current coronavirus disease 2019 (COVID-19). Since the beginning of the pandemic, the protection conferred by vaccination with the original strain has been threatened by the emergence of new variants of concern (VOCs) (1). In December 2020, an alpha variant (B.1.1.7) and a beta variant (B.1.351) were publicly announced as VOCs and spread worldwide. They were followed by a gamma strain (P.1), which was publicly announced as a VOC in January 2021. Both the beta and gamma variants showed remarkable resistance to neutralizing antibodies raised against the original strain in humans (1, 2). In May 2021, a large outbreak occurred in India, giving rise to a new VOC, the delta variant (B.1.617.2). This new VOC harbors mutations during the spike that are distinct from other variants. This mutation also results in a significant decrease in susceptibility to neutralizing antibodies and increased infectivity, rapidly replacing previous variants worldwide (1, 3). In November 2021, a new VOC named Omicron emerged in South Africa. Since that moment, Omicron has been replacing delta variants worldwide (4). Compared to previous VOCs, Omicron has the most mutations in the spike protein and shows the highest reduction in neutralizing activity (5, 6). Currently, a sublineage of Omicron, BA.2, also known as "stealth" Omicron, seems to display further immune evasion and infectivity (7-9).

[0006] Despite unprecedented rapid development of COVID-19 vaccines, only 63.1% of the global population has been fully vaccinated (6). Therefore, there remains a need for a COVID-19 vaccine that can be produced locally in low- and middle-income countries (LMICs), which have the lowest vaccination rates in the world (6). Summary of the Invention

[0007] 3. Overview of the Invention In one aspect, described herein is a nucleotide sequence comprising the spike protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) or a portion thereof (e.g., the extracellular domain or receptor binding domain of the SARS-CoV-2 spike protein) or a derivative thereof. In one embodiment, provided herein is a nucleotide sequence encoding the SARS-CoV-2 extracellular domain or a derivative thereof (e.g., a derivative of the extracellular domain of the SARS-CoV-2 spike protein described herein, such as in Section 5.1.2 or 6 herein). In some embodiments, provided herein is a nucleotide sequence encoding a derivative of the SARS-CoV-2 extracellular domain. In some embodiments, the derivative of the SARS-CoV-2 extracellular domain comprises the amino acid sequence of SEQ ID NO: 12, 13, 16, 17, 23, 24, 29, or 30. In some embodiments, a derivative of the SARS-CoV-2 extracellular domain comprises an amino acid sequence that is 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: 12, 13, 16, 17, 23, 24, 29, or 30. In some embodiments, provided herein is a nucleotide sequence encoding a protein comprising the extracellular domain of the SARS-CoV-2 spike protein or a derivative thereof. In some embodiments, provided herein is a nucleotide sequence encoding a protein comprising a derivative of the extracellular domain of the SARS-CoV-2 spike protein. In some embodiments, a derivative of the SARS-CoV-2 extracellular domain comprises the amino acid sequence of SEQ ID NO: 12, 13, 16, 17, 23, 24, 29, or 30. In some embodiments, a derivative of the SARS-CoV-2 extracellular domain comprises an amino acid sequence that is 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: 12, 13, 16, 17, 23, 24, 29, or 30.In certain embodiments, provided herein is a nucleotide sequence encoding a chimeric F protein comprising an extracellular domain of a SARS-CoV-2 spike protein, or a derivative thereof, and a transmembrane domain and a cytoplasmic domain of a NDV F protein. In some embodiments, provided herein is a nucleotide sequence encoding a chimeric F protein comprising a derivative of an extracellular domain of a SARS-CoV-2 spike protein (e.g., a derivative of an extracellular domain of a SARS-CoV-2 spike protein described herein, such as in Section 5.1.2 or 6), and a transmembrane domain and a cytoplasmic domain of a NDV F protein. In some embodiments, a derivative of a SARS-CoV-2 extracellular domain comprises the amino acid sequence of SEQ ID NO: 12, 13, 16, 17, 23, 24, 29, or 30. In some embodiments, the derivative of the SARS-CoV-2 extracellular domain comprises an amino acid sequence that is 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: 12, 13, 16, 17, 23, 24, 29, or 30. In some embodiments, the transmembrane and cytoplasmic domains of the NDV F protein are those of the LaSota or Hitchner strain. In some embodiments, the transmembrane and cytoplasmic domains of the NDV F protein comprise SEQ ID NO: 42. In some embodiments, the derivative of the extracellular domain of the SARS-CoV-2 spike protein and the transmembrane and cytoplasmic domains of the NDV F protein are linked by a linker (e.g., a linker described herein, such as SEQ ID NO: 7) or directly linked. In some embodiments, the chimeric F protein comprises the amino acid sequence of SEQ ID NO: 6, 11, 18, 22, 28, 39, 40, or 41. In some embodiments, the chimeric F protein comprises an amino acid sequence that is 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: 6, 11, 18, 22, 28, 39, 40, or 41. In some embodiments, the nucleotide sequence is an RNA sequence.In some embodiments, the nucleotide sequence is a DNA sequence (e.g., cDNA). In some embodiments, the nucleotide sequence is present in a vector (e.g., a plasmid or virus). In some embodiments, provided herein is an immunogenic composition comprising such a nucleotide sequence. In some embodiments, the immunogenic composition comprises two or more of the nucleotide sequences described herein (e.g., the immunogenic composition is bivalent or multivalent).

[0008] In another aspect, described herein is a protein comprising the spike protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) or a portion thereof (e.g., the extracellular domain or receptor binding domain of the SARS-CoV-2 spike protein) or a derivative thereof. In one embodiment, provided herein is a protein comprising the SARS-CoV-2 extracellular domain or a derivative thereof (e.g., a derivative of the extracellular domain of the SARS-CoV-2 spike protein described herein, such as in Section 5.1.2 or 6 herein). In some embodiments, provided herein is a protein comprising a derivative of the SARS-CoV-2 extracellular domain. In some embodiments, the derivative of the SARS-CoV-2 extracellular domain comprises the amino acid sequence of SEQ ID NO: 12, 13, 16, 17, 23, 24, 29, or 30. In a particular embodiment, provided herein is a chimeric F protein comprising the extracellular domain of the SARS-CoV-2 spike protein, or a derivative thereof, and the transmembrane and cytoplasmic domains of the NDV F protein. In some embodiments, provided herein is a chimeric F protein comprising a derivative of the extracellular domain of the SARS-CoV-2 spike protein (e.g., a derivative of the extracellular domain of the SARS-CoV-2 spike protein described herein, such as in Section 5.1.2 or 6) and a transmembrane domain and a cytoplasmic domain of the NDV F protein. In some embodiments, the derivative of the SARS-CoV-2 extracellular domain comprises an amino acid sequence of SEQ ID NO: 12, 13, 16, 17, 23, 24, 29, or 30. In some embodiments, the derivative of the SARS-CoV-2 extracellular domain comprises an amino acid sequence that is 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: 12, 13, 16, 17, 23, 24, 29, or 30. In some embodiments, the transmembrane domain and the cytoplasmic domain of the NDV F protein are the domains of the LaSota or Hitchner strain. In some embodiments, the transmembrane and cytoplasmic domains of the NDV F protein comprise SEQ ID NO:42.In some embodiments, the derivative of the extracellular domain of the SARS-CoV-2 spike protein and the transmembrane and cytoplasmic domains of the NDV F protein are linked by a linker (e.g., a linker described herein, such as SEQ ID NO: 7) or directly linked. In some embodiments, the chimeric F protein comprises an amino acid sequence of SEQ ID NO: 6, 11, 18, 22, 28, 39, 40, or 41. In some embodiments, the chimeric F protein comprises an amino acid sequence that is 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: 6, 11, 18, 22, 28, 39, 40, or 41. In some embodiments, immunogenic compositions comprising such proteins or chimeric F proteins are provided herein. In some embodiments, the immunogenic composition comprises two or more of the proteins or chimeric F proteins described herein (e.g., the immunogenic composition is bivalent or multivalent).

[0009] In another aspect, described herein is a recombinant Newcastle Disease Virus (NDV) comprising a packaged genome, the packaged genome comprising a transgene encoding a spike protein of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), or a portion thereof (e.g., the extracellular domain or receptor binding domain of the SARS-CoV-2 spike protein), or a derivative thereof. In a particular embodiment, described herein is a recombinant NDV comprising a packaged genome, the packaged genome comprising a transgene comprising a codon-optimized nucleic acid sequence encoding a spike protein of SARS-CoV-2, or a portion thereof (e.g., the extracellular domain or receptor binding domain of the SARS-CoV-2 spike protein), or a derivative thereof. In a particular embodiment, described herein is a recombinant NDV comprising a packaged genome, the packaged genome comprising a transgene comprising a nucleic acid sequence encoding a protein comprising the extracellular domain of the spike protein of SARS-CoV-2, or a derivative thereof. In another specific embodiment, described herein is a recombinant NDV comprising a packaged genome, the packaged genome comprising a transgene comprising a nucleic acid sequence encoding a protein comprising a derivative of the extracellular domain of the spike protein of SARS-CoV-2. In a specific embodiment, described herein is a recombinant NDV comprising a packaged genome, the packaged genome comprising a transgene encoding a chimeric F protein, the chimeric F protein comprising the extracellular domain of the spike protein of SARS-CoV-2 or a derivative thereof, and the transmembrane and cytoplasmic domains of the NDV F protein. In a specific embodiment, described herein is a recombinant NDV comprising a packaged genome, the packaged genome comprising a transgene encoding a chimeric F protein, the chimeric F protein comprising the derivative of the extracellular domain of the spike protein of SARS-CoV-2, and the transmembrane and cytoplasmic domains of the NDV F protein.In some embodiments, the derivative of the SARS-CoV-2 ectodomain comprises an amino acid sequence of SEQ ID NO: 12, 13, 16, 17, 23, 24, 29, or 30. In some embodiments, the derivative of the SARS-CoV-2 ectodomain comprises an amino acid sequence that is at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to an amino acid sequence of SEQ ID NO: 12, 13, 16, 17, 23, 24, 29, or 30. In some embodiments, the ectodomain of the spike protein of SARS-CoV-2, or a derivative thereof, is encoded by a codon-optimized nucleic acid sequence. In some embodiments, the transmembrane and cytoplasmic domains of the NDV F protein are those of the LaSota or Hitchner strain. In some embodiments, the transmembrane and cytoplasmic domains of the NDV F protein comprise SEQ ID NO: 42. In some embodiments, the derivatives of the extracellular domain of the SARS-CoV-2 spike protein and the transmembrane and cytoplasmic domains of the NDV F protein are linked by a linker (e.g., a linker described herein, such as SEQ ID NO: 7) or directly.

[0010] In another aspect, provided herein is a recombinant Newcastle Disease Virus (NDV) comprising a spike protein or a portion thereof (e.g., an extracellular domain or a receptor binding domain of the SARS-CoV-2 spike protein) or a derivative thereof of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). In a particular embodiment, provided herein is a recombinant NDV comprising a protein comprising an extracellular domain of the SARS-CoV-2 spike protein or a derivative thereof. In another particular embodiment, provided herein is a recombinant NDV comprising a protein comprising a derivative of an extracellular domain of the SARS-CoV-2 spike protein. In another particular embodiment, provided herein is a recombinant NDV comprising a chimeric F protein comprising an extracellular domain of the SARS-CoV-2 spike protein or a derivative thereof, and a transmembrane domain and a cytoplasmic domain of the NDV F protein. In certain embodiments, provided herein is a recombinant NDV comprising a chimeric F protein, the chimeric F protein comprising a derivative of the extracellular domain of the SARS-CoV-2 spike protein and the transmembrane and cytoplasmic domains of the NDV F protein. In some embodiments, the derivative of the SARS-CoV-2 extracellular domain comprises the amino acid sequence of SEQ ID NO: 12, 13, 16, 17, 23, 24, 29, or 30. In some embodiments, the derivative of the SARS-CoV-2 extracellular domain comprises an amino acid sequence that is 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: 12, 13, 16, 17, 23, 24, 29, or 30. In some embodiments, the extracellular domain of the spike protein of SARS-CoV-2, or a derivative thereof, is encoded by a codon-optimized nucleic acid sequence. In some embodiments, the transmembrane and cytoplasmic domains of the NDV F protein are those of the LaSota or Hitchner strain. In some embodiments, the transmembrane and cytoplasmic domains of the NDV F protein comprise SEQ ID NO:42.In some embodiments, the derivatives of the extracellular domain of the SARS-CoV-2 spike protein and the transmembrane and cytoplasmic domains of the NDV F protein are linked by a linker (e.g., a linker described herein, such as SEQ ID NO: 7) or directly.

[0011] In another aspect, provided herein is an immunogenic composition comprising a recombinant NDV as described herein. The immunogenic composition may be monovalent, bivalent, or multivalent. In some embodiments, the immunogenic composition is monovalent. In some embodiments, the immunogenic composition is bivalent. In some embodiments, the immunogenic composition is trivalent. In some embodiments, the immunogenic composition is tetravalent.

[0012] In some embodiments, provided herein is an immunogenic composition comprising: (a) a first recombinant NDV, the first recombinant NDV comprising a first transgene comprising a nucleotide sequence encoding a first chimeric F protein, the first chimeric F protein comprising a first derivative of the extracellular domain of a SARS-CoV-2 spike protein, and a transmembrane domain and a cytoplasmic domain of a NDV F protein; and (b) a second recombinant NDV, the second recombinant NDV comprising a second transgene comprising a nucleotide sequence encoding a second chimeric F protein, the second chimeric F protein comprising a second derivative of the extracellular domain of a SARS-CoV-2 spike protein, and a transmembrane domain and a cytoplasmic domain of a NDV F protein, wherein the first derivative and the second derivative are different from each other. In certain embodiments, a derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) lacks a polybasic cleavage site (e.g., one, two, or more residues corresponding to amino acid residues 682-685 (RRAR) of GenBank Accession No. MN908947.3 are replaced with other amino acid residues). In certain embodiments, lacking a polybasic cleavage site means that the polybasic site is altered such that it is not cleaved, for example, by furin. In certain embodiments, the amino acid residues corresponding to amino acid residues 682-685 (RRAR) of GenBank Accession No. MN908947.3 are replaced with an alanine. In some embodiments, a derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) contains the following amino acid substitutions at amino acid residues corresponding to amino acid residues in GenBank Accession No. MN908947.3: F817P, A892P, A899P, A942P, K986P, and V987P.

[0013] In some embodiments, a first derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises an amino acid sequence of SEQ ID NO: 12 or 16, or 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: 12 or 16. In some embodiments, a second derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises an amino acid sequence of SEQ ID NO: 13, 17, 23, 24, 29 or 30, or 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: 13, 17, 23, 24, 29 or 30. In some embodiments, a first derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises an amino acid sequence of SEQ ID NO: 23 or 24, or 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: 23 or 24. In some embodiments, a second derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises an amino acid sequence of SEQ ID NO: 13, 17, 29 or 30, or 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: 13, 17, 29 or 30. In some embodiments, the first derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises an amino acid sequence of SEQ ID NO: 29 or 30, or 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: 29 or 30.In some embodiments, the second derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises an amino acid sequence of SEQ ID NO: 13 or 17, or 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: 13 or 17. In some embodiments, the nucleotide sequence encoding the chimeric F protein is codon optimized.

[0014] In some embodiments, the present disclosure provides a method for the preparation of NDV vectors comprising the steps of: (a) a first recombinant NDV, the first recombinant NDV comprising a first transgene comprising a nucleotide sequence encoding a first chimeric F protein, the first chimeric F protein comprising a first derivative of the extracellular domain of a SARS-CoV-2 spike protein, and a transmembrane domain and a cytoplasmic domain of an NDV F protein; (b) a second recombinant NDV, the second recombinant NDV comprising a second transgene comprising a nucleotide sequence encoding a second chimeric F protein, the second chimeric F protein comprising a second derivative of the extracellular domain of a SARS-CoV-2 spike protein, and a transmembrane domain and a cytoplasmic domain of an NDV F protein; and (c) a third recombinant NDV, the third recombinant NDV comprising a third transgene comprising a nucleotide sequence encoding a third chimeric F protein, the third chimeric F protein comprising a third derivative of the extracellular domain of a SARS-CoV-2 spike protein, and a transmembrane domain and a cytoplasmic domain of an NDV F protein. A multivalent immunogenic composition is provided, comprising a transmembrane domain and a cytoplasmic domain of the F protein, wherein the first derivative, the second derivative, and the third derivative are different from each other. In certain embodiments, a derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) lacks a polybasic cleavage site (e.g., one, two, or more residues corresponding to amino acid residues 682-685 (RRAR) of GenBank Accession No. MN908947.3 are replaced with other amino acid residues). In certain embodiments, lacking a polybasic cleavage site means that the polybasic site is altered so that it is not cleaved, for example, by furin. In certain embodiments, the amino acid residues corresponding to amino acid residues 682-685 (RRAR) of GenBank Accession No. MN908947.3 are replaced with an alanine.In some embodiments, a derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) comprises the following amino acid substitutions at amino acid residues corresponding to amino acid residues in GenBank Accession No. MN908947.3: F817P, A892P, A899P, A942P, K986P, and V987P. In some embodiments, a first derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises an amino acid sequence of SEQ ID NO: 12 or 16, or an amino acid sequence 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: 12 or 16. In some embodiments, the second derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises an amino acid sequence of SEQ ID NO: 13 or 17, or 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: 13 or 17. In some embodiments, the third derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises an amino acid sequence of SEQ ID NO: 29 or 30, or 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: 29 or 30. In some embodiments, the first derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises an amino acid sequence of SEQ ID NO: 23 or 24, or 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: 23 or 24. In some embodiments, the second derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises an amino acid sequence of SEQ ID NO: 13 or 17, or 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: 13 or 17.In some embodiments, the second derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises an amino acid sequence of SEQ ID NO: 12 or 16, or 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: 12 or 16. In some embodiments, the third derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises an amino acid sequence of SEQ ID NO: 29 or 30, or 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: 29 or 30. In some embodiments, the first derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises an amino acid sequence of SEQ ID NO: 29 or 30, or 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: 29 or 30. In some embodiments, a first derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises an amino acid sequence of SEQ ID NO: 13 or 17, or 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: 13 or 17. In some embodiments, a second derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises an amino acid sequence of SEQ ID NO: 13 or 17, or 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: 13 or 17.In some embodiments, the immunogenic composition further comprises a fourth recombinant NDV, the fourth recombinant NDV comprising a fourth transgene comprising a nucleotide sequence encoding a fourth chimeric F protein, the fourth chimeric F protein comprising a fourth derivative of the extracellular domain of the SARS-CoV-2 spike protein and the transmembrane and cytoplasmic domains of the NDV F protein, the fourth derivative being different from the first derivative, the second derivative, and the third derivative. In some embodiments, the fourth recombinant NDV comprises a fourth transgene comprising a nucleotide sequence encoding a fourth chimeric F protein, the fourth derivative of the extracellular domain of the SARS-CoV-2 spike protein comprising an amino acid sequence of SEQ ID NO: 23 or 24, or an amino acid sequence 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: 23 or 24. In some embodiments, the nucleotide sequence encoding the chimeric F protein is codon-optimized.

[0015] In some embodiments, provided herein is an immunogenic composition comprising: (a) a first recombinant NDV comprising a first chimeric F protein, the first chimeric F protein comprising a first derivative of the extracellular domain of SARS-CoV-2 spike protein, and a transmembrane domain and a cytoplasmic domain of an NDV F protein; and (b) a second recombinant NDV comprising a second chimeric F protein, the second chimeric F protein comprising a second derivative of the extracellular domain of SARS-CoV-2 spike protein, and a transmembrane domain and a cytoplasmic domain of an NDV F protein, wherein the first derivative and the second derivative are different from each other. In certain embodiments, a derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) lacks a polybasic cleavage site (e.g., one, two, or more residues corresponding to amino acid residues 682-685 (RRAR) of GenBank Accession No. MN908947.3 are replaced with other amino acid residues). In certain embodiments, lacking a polybasic cleavage site means that the polybasic site is altered such that it is not cleaved, for example, by furin. In certain embodiments, the amino acid residues corresponding to amino acid residues 682-685 (RRAR) of GenBank Accession No. MN908947.3 are replaced with an alanine. In some embodiments, a derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) contains the following amino acid substitutions at amino acid residues corresponding to amino acid residues in GenBank Accession No. MN908947.3: F817P, A892P, A899P, A942P, K986P, and V987P.In some embodiments, a first derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises an amino acid sequence of SEQ ID NO: 12 or 16, or 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: 12 or 16. In some embodiments, a second derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises an amino acid sequence of SEQ ID NO: 13, 17, 23, 24, 29 or 30, or 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: 13, 17, 23, 24, 29 or 30. In some embodiments, a first derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises an amino acid sequence of SEQ ID NO: 23 or 24, or 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: 23 or 24. In some embodiments, a second derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises an amino acid sequence of SEQ ID NO: 13, 17, 29, or 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: 13, 17, 29, or 30. In some embodiments, the first derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises an amino acid sequence of SEQ ID NO: 29 or 30, or 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: 29 or 30.In some embodiments, the second derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises an amino acid sequence of SEQ ID NO: 13 or 17, or 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: 13 or 17.

[0016] In some embodiments, provided herein are multivalent immunogenic compositions comprising: (a) a first recombinant NDV comprising a first chimeric F protein, the first chimeric F protein comprising a first derivative of the extracellular domain of SARS-CoV-2 spike protein, and a transmembrane domain and a cytoplasmic domain of an NDV F protein; (b) a second recombinant NDV comprising a second chimeric F protein, the second chimeric F protein comprising a second derivative of the extracellular domain of SARS-CoV-2 spike protein, and a transmembrane domain and a cytoplasmic domain of an NDV F protein; and (c) a third recombinant NDV comprising a third chimeric F protein, the third chimeric F protein comprising a third derivative of the extracellular domain of SARS-CoV-2 spike protein, and a transmembrane domain and a cytoplasmic domain of an NDV F protein, wherein the first derivative, second derivative, and third derivative are different from each other. In certain embodiments, a derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) lacks a polybasic cleavage site (e.g., one, two, or more residues corresponding to amino acid residues 682-685 (RRAR) of GenBank Accession No. MN908947.3 are replaced with other amino acid residues). In certain embodiments, lacking a polybasic cleavage site means that the polybasic site is altered such that it is not cleaved, for example, by furin. In certain embodiments, the amino acid residues corresponding to amino acid residues 682-685 (RRAR) of GenBank Accession No. MN908947.3 are replaced with an alanine. In some embodiments, a derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) contains the following amino acid substitutions at amino acid residues corresponding to amino acid residues in GenBank Accession No. MN908947.3: F817P, A892P, A899P, A942P, K986P, and V987P.In some embodiments, a first derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises an amino acid sequence of SEQ ID NO: 12 or 16, or 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: 12 or 16. In some embodiments, a second derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises an amino acid sequence of SEQ ID NO: 13 or 17, or 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: 13 or 17. In some embodiments, a third derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises an amino acid sequence of SEQ ID NO: 29 or 30, or 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: 29 or 30. In some embodiments, a first derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises an amino acid sequence of SEQ ID NO: 23 or 24, or 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: 23 or 24. In some embodiments, a second derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises an amino acid sequence of SEQ ID NO: 13 or 17, or 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: 13 or 17. In some embodiments, a second derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises an amino acid sequence of SEQ ID NO: 12 or 16, or 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: 12 or 16.In some embodiments, the third derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises an amino acid sequence of SEQ ID NO: 29 or 30, or 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: 29 or 30. In some embodiments, the first derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises an amino acid sequence of SEQ ID NO: 29 or 30, or 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: 29 or 30. In some embodiments, the first derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises an amino acid sequence of SEQ ID NO: 13 or 17, or 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: 13 or 17. In some embodiments, the second derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises an amino acid sequence of SEQ ID NO: 13 or 17, or an amino acid sequence 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: 13 or 17. In some embodiments, the immunogenic composition further comprises a fourth recombinant NDV comprising a fourth chimeric F protein, the fourth chimeric F protein comprising a fourth derivative of the extracellular domain of the SARS-CoV-2 spike protein and the transmembrane and cytoplasmic domains of the NDV F protein, the fourth derivative being different from the first derivative, the second derivative, and the third derivative.In some embodiments, the fourth recombinant NDV comprises a fourth chimeric F protein, wherein the fourth derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises an amino acid sequence of SEQ ID NO: 23 or 24, or an amino acid sequence 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: 23 or 24. In some embodiments, the nucleotide sequence encoding the chimeric F protein is codon optimized.

[0017] In certain embodiments, a derivative of the extracellular domain of the SARS-CoV-2 spike protein comprises amino acid substitutions of proline at positions corresponding to positions 817, 892, 899, 942, 986, and 987 of the Wuhan strain spike protein (see GenBank Accession No. MN908947.3), and RRAR to alanine substitutions at positions corresponding to positions 682-685 of the Wuhan strain spike protein (see GenBank Accession No. MN908947.3).

[0018] In some embodiments, the first derivative of the extracellular domain of the SARS-CoV-2 spike protein and the second derivative of the extracellular domain of the SARS-CoV-2 spike protein have less than 85% identity with each other. In some embodiments, the first derivative of the extracellular domain of the SARS-CoV-2 spike protein and the second derivative of the extracellular domain of the SARS-CoV-2 spike protein have less than 90% identity with each other. In some embodiments, the first derivative of the extracellular domain of the SARS-CoV-2 spike protein and the second derivative of the extracellular domain of the SARS-CoV-2 spike protein have less than 95% identity with each other. In some embodiments, the first derivative of the extracellular domain of the SARS-CoV-2 spike protein and the second derivative of the extracellular domain of the SARS-CoV-2 spike protein have less than 98% identity with each other. In some embodiments, the first derivative of the extracellular domain of the SARS-CoV-2 spike protein and the second derivative of the extracellular domain of the SARS-CoV-2 spike protein have less than 99% identity to each other. In some embodiments, the first derivative of the extracellular domain of the SARS-CoV-2 spike protein and the second derivative of the extracellular domain of the SARS-CoV-2 spike protein have 75%-90% identity to each other. In some embodiments, the first derivative of the extracellular domain of the SARS-CoV-2 spike protein and the second derivative of the extracellular domain of the SARS-CoV-2 spike protein have 85%-90% identity to each other. In some embodiments, the first derivative of the extracellular domain of the SARS-CoV-2 spike protein and the second derivative of the extracellular domain of the SARS-CoV-2 spike protein have 90%-95% identity to each other. In some embodiments, the first derivative of the extracellular domain of the SARS-CoV-2 spike protein and the second derivative of the extracellular domain of the SARS-CoV-2 spike protein have 95% to 99% identity to each other.

[0019] In some embodiments, the first derivative of the extracellular domain of the SARS-CoV-2 spike protein, the second derivative of the extracellular domain of the SARS-CoV-2 spike protein, and the third derivative of the extracellular domain of the SARS-CoV-2 spike protein have less than 85% identity with each other. In some embodiments, the first derivative of the extracellular domain of the SARS-CoV-2 spike protein, the second derivative of the extracellular domain of the SARS-CoV-2 spike protein, and the third derivative of the extracellular domain of the SARS-CoV-2 spike protein have less than 90% identity with each other. In some embodiments, the first derivative of the extracellular domain of the SARS-CoV-2 spike protein, the second derivative of the extracellular domain of the SARS-CoV-2 spike protein, and the third derivative of the extracellular domain of the SARS-CoV-2 spike protein have less than 95% identity with each other. In some embodiments, the first derivative of the extracellular domain of the SARS-CoV-2 spike protein, the second derivative of the extracellular domain of the SARS-CoV-2 spike protein, and the third derivative of the extracellular domain of the SARS-CoV-2 spike protein have less than 98% identity with each other. In some embodiments, the first derivative of the extracellular domain of the SARS-CoV-2 spike protein, the second derivative of the extracellular domain of the SARS-CoV-2 spike protein, and the third derivative of the extracellular domain of the SARS-CoV-2 spike protein have less than 99% identity with each other. In some embodiments, the first derivative of the extracellular domain of the SARS-CoV-2 spike protein, the second derivative of the extracellular domain of the SARS-CoV-2 spike protein, and the third derivative of the extracellular domain of the SARS-CoV-2 spike protein have between 75% and 90% identity with each other. In some embodiments, the first derivative of the extracellular domain of the SARS-CoV-2 spike protein, the second derivative of the extracellular domain of the SARS-CoV-2 spike protein, and the third derivative of the extracellular domain of the SARS-CoV-2 spike protein have 85%-90% identity to each other.In some embodiments, the first derivative of the extracellular domain of the SARS-CoV-2 spike protein, the second derivative of the extracellular domain of the SARS-CoV-2 spike protein, and the third derivative of the extracellular domain of the SARS-CoV-2 spike protein have 90%-95% identity with each other. In some embodiments, the first derivative of the extracellular domain of the SARS-CoV-2 spike protein, the second derivative of the extracellular domain of the SARS-CoV-2 spike protein, and the third derivative of the extracellular domain of the SARS-CoV-2 spike protein have 95%-99% identity with each other.

[0020] In some embodiments, the first derivative of the extracellular domain of the SARS-CoV-2 spike protein, the second derivative of the extracellular domain of the SARS-CoV-2 spike protein, the third derivative of the extracellular domain of the SARS-CoV-2 spike protein, and the fourth derivative of the extracellular domain of the SARS-CoV-2 spike protein have less than 85% identity to each other. In some embodiments, the first derivative of the extracellular domain of the SARS-CoV-2 spike protein, the second derivative of the extracellular domain of the SARS-CoV-2 spike protein, the third derivative of the extracellular domain of the SARS-CoV-2 spike protein, and the fourth derivative of the extracellular domain of the SARS-CoV-2 spike protein have less than 90% identity to each other. In some embodiments, the first derivative of the extracellular domain of the SARS-CoV-2 spike protein, the second derivative of the extracellular domain of the SARS-CoV-2 spike protein, the third derivative of the extracellular domain of the SARS-CoV-2 spike protein, and the fourth derivative of the extracellular domain of the SARS-CoV-2 spike protein have less than 95% identity to each other. In some embodiments, the first derivative of the extracellular domain of the SARS-CoV-2 spike protein, the second derivative of the extracellular domain of the SARS-CoV-2 spike protein, the third derivative of the extracellular domain of the SARS-CoV-2 spike protein, and the fourth derivative of the extracellular domain of the SARS-CoV-2 spike protein have less than 98% identity to each other. In some embodiments, the first derivative of the extracellular domain of the SARS-CoV-2 spike protein, the second derivative of the extracellular domain of the SARS-CoV-2 spike protein, the third derivative of the extracellular domain of the SARS-CoV-2 spike protein, and the fourth derivative of the extracellular domain of the SARS-CoV-2 spike protein have less than 99% identity to each other.In some embodiments, the first derivative of the extracellular domain of the SARS-CoV-2 spike protein, the second derivative of the extracellular domain of the SARS-CoV-2 spike protein, the third derivative of the extracellular domain of the SARS-CoV-2 spike protein, and the fourth derivative of the extracellular domain of the SARS-CoV-2 spike protein have 75%-90% identity with each other. In some embodiments, the first derivative of the extracellular domain of the SARS-CoV-2 spike protein, the second derivative of the extracellular domain of the SARS-CoV-2 spike protein, the third derivative of the extracellular domain of the SARS-CoV-2 spike protein, and the fourth derivative of the extracellular domain of the SARS-CoV-2 spike protein have 85%-90% identity with each other. In some embodiments, the first derivative of the extracellular domain of the SARS-CoV-2 spike protein, the second derivative of the extracellular domain of the SARS-CoV-2 spike protein, the third derivative of the extracellular domain of the SARS-CoV-2 spike protein, and the fourth derivative of the extracellular domain of the SARS-CoV-2 spike protein have 90% to 95% identity with each other. In some embodiments, the first derivative of the extracellular domain of the SARS-CoV-2 spike protein, the second derivative of the extracellular domain of the SARS-CoV-2 spike protein, the third derivative of the extracellular domain of the SARS-CoV-2 spike protein, and the fourth derivative of the extracellular domain of the SARS-CoV-2 spike protein have 95% to 99% identity with each other.

[0021] In some embodiments, the extracellular domain of the chimeric F protein is linked to the transmembrane and cytoplasmic domains of the NDV F protein via a linker. In certain embodiments, the linker comprises the amino acid sequence of SEQ ID NO: 7. In some embodiments, the NDV F protein and cytoplasmic domain comprise the amino acid sequence of SEQ ID NO: 42, or an amino acid sequence at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to SEQ ID NO: 42.

[0022] In some embodiments, the transmembrane and cytoplasmic domains of the NDV F protein are the transmembrane and cytoplasmic domains of the F protein of the NDV LaSota strain. In some embodiments, the transmembrane and cytoplasmic domains of the NDV F protein are the transmembrane and cytoplasmic domains of the F protein of the NDV Hitchner strain. In some embodiments, the transmembrane and cytoplasmic domains of the NDV F protein comprise the amino acid sequence of SEQ ID NO:42.

[0023] In some embodiments, reference is made herein to (a) a first recombinant NDV, the first recombinant NDV comprising a first transgene comprising a nucleotide sequence encoding a first chimeric F protein, the first chimeric F protein comprising an amino acid sequence of SEQ ID NO: 11 or 40, or 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: 11 or 40; and (b) a second recombinant NDV comprising a first transgene comprising a nucleotide sequence encoding a first chimeric F protein, the first chimeric F protein comprising an amino acid sequence of SEQ ID NO: 11 or 40, or 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: 11 or 40. Immunogenic compositions are provided that include a recombinant NDV, the second recombinant NDV comprising a second transgene comprising a nucleotide sequence encoding a second chimeric F protein, the second chimeric F protein comprising an amino acid sequence of SEQ ID NO: 6, 18, 22, 28, 39, or 41, or 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: 6, 18, 22, 28, 39, or 41. In some embodiments, provided herein is an immunogenic composition comprising: (a) a first recombinant NDV, the first recombinant NDV comprising a first transgene comprising a nucleotide sequence encoding a first chimeric F protein, the first chimeric F protein comprising an amino acid sequence of SEQ ID NO: 28 or 41, or 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: 28 or 41; and (b) a second recombinant NDV, the second recombinant NDV comprising a second transgene comprising a nucleotide sequence encoding a second chimeric F protein, the second chimeric F protein comprising an amino acid sequence of SEQ ID NO: 6, 18, 22, or 39, or 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: 6, 18, 22, or 39.In some embodiments, provided herein is an immunogenic composition comprising: (a) a first recombinant NDV, the first recombinant NDV comprising a first transgene comprising a nucleotide sequence encoding a first chimeric F protein, the first chimeric F protein comprising an amino acid sequence of SEQ ID NO: 28 or 41, or 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: 28 or 41; and (b) a second recombinant NDV, the second recombinant NDV comprising a second transgene comprising a nucleotide sequence encoding a second chimeric F protein, the second chimeric F protein comprising an amino acid sequence of SEQ ID NO: 6, 18, 22, or 39, or 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: 6, 18, 22, or 39. In some embodiments, provided herein is an immunogenic composition comprising: (a) a first recombinant NDV, the first recombinant NDV comprising a first transgene comprising a nucleotide sequence encoding a first chimeric F protein, the first chimeric F protein comprising an amino acid sequence of SEQ ID NO: 28 or 41, or 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: 28 or 41; and (b) a second recombinant NDV, the second recombinant NDV comprising a second transgene comprising a nucleotide sequence encoding a second chimeric F protein, the second chimeric F protein comprising an amino acid sequence of SEQ ID NO: 11 or 40, or 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: 11 or 40.In some embodiments, provided herein is an immunogenic composition comprising: (a) a first recombinant NDV, the first recombinant NDV comprising a first transgene comprising a nucleotide sequence encoding a first chimeric F protein, the first chimeric F protein comprising an amino acid sequence of SEQ ID NO: 22 or 39, or 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: 22 or 39; and (b) a second recombinant NDV, the second recombinant NDV comprising a second transgene comprising a nucleotide sequence encoding a second chimeric F protein, the second chimeric F protein comprising an amino acid sequence of SEQ ID NO: 28 or 41, or 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: 28 or 41. In some embodiments, provided herein is an immunogenic composition comprising: (a) a first recombinant NDV, the first recombinant NDV comprising a first transgene comprising a nucleotide sequence encoding a first chimeric F protein, the first chimeric F protein comprising an amino acid sequence of SEQ ID NO: 22 or 39, or 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: 22 or 39; and (b) a second recombinant NDV, the second recombinant NDV comprising a second transgene comprising a nucleotide sequence encoding a second chimeric F protein, the second chimeric F protein comprising an amino acid sequence of SEQ ID NO: 6 or 18, or 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: 6 or 18.In some embodiments, provided herein is an immunogenic composition comprising: (a) a first recombinant NDV, the first recombinant NDV comprising a first transgene comprising a nucleotide sequence encoding a first chimeric F protein, the first chimeric F protein comprising an amino acid sequence of SEQ ID NO: 22 or 39, or 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: 22 or 39, and (b) a second recombinant NDV, the second recombinant NDV comprising a second transgene comprising a nucleotide sequence encoding a second chimeric F protein, the second chimeric F protein comprising an amino acid sequence of SEQ ID NO: 11 or 40, or 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: 11 or 40. In some embodiments, the nucleotide sequence encoding the chimeric F protein is codon optimized.

[0024] In some embodiments, reference is made herein to (a) a first recombinant NDV, the first recombinant NDV comprising a first transgene comprising a nucleotide sequence encoding a first chimeric F protein, the first chimeric F protein comprising an amino acid sequence of SEQ ID NO: 11 or 40, or 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: 11 or 40; (b) a second recombinant NDV, the second recombinant NDV comprising a second transgene comprising a nucleotide sequence encoding a second chimeric F protein, the second chimeric F protein comprising an amino acid sequence of SEQ ID NO: 22 or 39, or 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: 22 or 39. or 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: 22 or 39, and (c) a third recombinant NDV, the third recombinant NDV comprising a third transgene comprising a nucleotide sequence encoding a third chimeric F protein, the third chimeric F protein comprising an amino acid sequence of SEQ ID NO: 6, 18, 28 or 41, or 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: 6, 18, 28 or 41. In some embodiments, the nucleotide sequence encoding the chimeric F protein is codon optimized.

[0025] In some embodiments, a recombinant NDV is provided herein: (a) a first recombinant NDV, the first recombinant NDV comprising a first transgene comprising a nucleotide sequence encoding a first chimeric F protein, the first chimeric F protein comprising an amino acid sequence of SEQ ID NO: 28 or 41, or 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: 28 or 41; (b) a second recombinant NDV, the second recombinant NDV comprising a second transgene comprising a nucleotide sequence encoding a second chimeric F protein, the second chimeric F protein comprising an amino acid sequence of SEQ ID NO: 22 or 39. and (c) a third recombinant NDV 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 SEQ ID NO: 22 or 39, or the amino acid sequence of SEQ ID NO: 22 or 39, and (c) a third recombinant NDV comprising a third transgene comprising a nucleotide sequence encoding a third chimeric F protein, the third chimeric F protein 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 SEQ ID NO: 28 or 41, or the amino acid sequence of SEQ ID NO: 6 or 18. In some embodiments, the nucleotide sequence encoding the chimeric F protein is codon optimized.

[0026] In some embodiments, the term herein includes: (a) a first recombinant NDV, the first recombinant NDV comprising a first transgene comprising a nucleotide sequence encoding a first chimeric F protein, the first chimeric F protein comprising an amino acid sequence of SEQ ID NO: 11 or 40, or 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: 11 or 40; (b) a second recombinant NDV, the second recombinant NDV comprising a second transgene comprising a nucleotide sequence encoding a second chimeric F protein, the second chimeric F protein comprising an amino acid sequence of SEQ ID NO: 22 or 39, or 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: 22 or 39; Multivalent immunogenic compositions are provided that include: (c) a third recombinant NDV, the third recombinant NDV comprising a third transgene comprising a nucleotide sequence encoding a third chimeric F protein, the third chimeric F protein comprising an amino acid sequence of SEQ ID NO: 6 or 18, or 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: 6 or 18; and (d) a fourth recombinant NDV, the fourth recombinant NDV comprising a fourth transgene comprising a nucleotide sequence encoding a fourth chimeric F protein, the fourth chimeric F protein comprising an amino acid sequence of SEQ ID NO: 28 or 41, or 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: 28 or 41. In some embodiments, the nucleotide sequence encoding the chimeric F protein is codon optimized.

[0027] In some embodiments, provided herein is an immunogenic composition comprising: (a) a first recombinant NDV comprising a first chimeric F protein, wherein the first chimeric F protein comprises an amino acid sequence of SEQ ID NO: 11 or 40, or 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: 11 or 40; and (b) a second recombinant NDV comprising a second chimeric F protein, wherein the second chimeric F protein comprises an amino acid sequence of SEQ ID NO: 6, 18, 22, 28, 39, or 41, or 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: 6, 18, 22, 28, 39, or 41. In some embodiments, provided herein is an immunogenic composition comprising: (a) a first recombinant NDV comprising a first chimeric F protein, wherein the first chimeric F protein comprises an amino acid sequence of SEQ ID NO: 28 or 41, or 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: 28 or 41; and (b) a second recombinant NDV comprising a second chimeric F protein, wherein the second chimeric F protein comprises an amino acid sequence of SEQ ID NO: 6, 18, 22, or 39, or 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: 6, 18, 22, or 39.In some embodiments, provided herein is an immunogenic composition comprising: (a) a first recombinant NDV comprising a first chimeric F protein, wherein the first chimeric F protein comprises an amino acid sequence of SEQ ID NO: 28 or 41, or 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: 28 or 41; and (b) a second recombinant NDV comprising a second chimeric F protein, wherein the second chimeric F protein comprises an amino acid sequence of SEQ ID NO: 6, 18, 22, or 39, or 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: 6, 18, 22, or 39. In some embodiments, provided herein is an immunogenic composition comprising: (a) a first recombinant NDV, the first recombinant NDV comprising a first chimeric F protein, the first chimeric F protein comprising an amino acid sequence of SEQ ID NO: 28 or 41, or 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: 28 or 41; and (b) a second recombinant NDV, the second recombinant NDV comprising a second chimeric F protein, the second chimeric F protein comprising an amino acid sequence of SEQ ID NO: 11 or 40, or 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: 11 or 40.In some embodiments, provided herein is an immunogenic composition comprising: (a) a first recombinant NDV, the first recombinant NDV comprising a first chimeric F protein, the first chimeric F protein comprising an amino acid sequence of SEQ ID NO: 22 or 39, or 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: 22 or 39; and (b) a second recombinant NDV, the second recombinant NDV comprising a second chimeric F protein, the second chimeric F protein comprising an amino acid sequence of SEQ ID NO: 28 or 41, or 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: 28 or 41. In some embodiments, provided herein is an immunogenic composition comprising: (a) a first recombinant NDV, the first recombinant NDV comprising a first chimeric F protein, the first chimeric F protein comprising an amino acid sequence of SEQ ID NO: 22 or 39, or 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: 22 or 39; and (b) a second recombinant NDV, the second recombinant NDV comprising a second chimeric F protein, the second chimeric F protein comprising an amino acid sequence of SEQ ID NO: 6 or 18, or 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: 6 or 18.In some embodiments, provided herein is an immunogenic composition comprising: (a) a first recombinant NDV, the first recombinant NDV comprising a first chimeric F protein, the first chimeric F protein comprising an amino acid sequence of SEQ ID NO: 22 or 39, or 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: 22 or 39; and (b) a second recombinant NDV, the second recombinant NDV comprising a second chimeric F protein, the second chimeric F protein comprising an amino acid sequence of SEQ ID NO: 11 or 40, or 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: 11 or 40.

[0028] In some embodiments, reference is made herein to (a) a first recombinant NDV comprising a first chimeric F protein, wherein the first chimeric F protein comprises an amino acid sequence of SEQ ID NO: 11 or 40, or 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: 11 or 40; (b) a second recombinant NDV comprising a second chimeric F protein, wherein the second chimeric F protein comprises an amino acid sequence of SEQ ID NO: 22 or 39, or 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: 22 or 39. and (c) a third recombinant NDV comprising a third chimeric F protein, wherein the third chimeric F protein comprises an amino acid sequence of SEQ ID NO: 6, 18, 28 or 41, or 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: 6, 18, 28 or 41.In some embodiments, provided herein is (a) a first recombinant NDV comprising a first chimeric F protein, wherein the first chimeric F protein comprises an amino acid sequence of SEQ ID NO: 28 or 41, or 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: 28 or 41; (b) a second recombinant NDV comprising a second chimeric F protein, wherein the second chimeric F protein comprises an amino acid sequence of SEQ ID NO: 22 or 39, or 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: 22 or 39. and (c) a third recombinant NDV comprising a third chimeric F protein, wherein the third chimeric F protein 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: 28 or 41, or the amino acid sequence of SEQ ID NO: 6 or 18.In some embodiments, reference is made herein to (a) a first recombinant NDV comprising a first chimeric F protein, wherein the first chimeric F protein comprises an amino acid sequence of SEQ ID NO: 11 or 40, or 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: 11 or 40; (b) a second recombinant NDV comprising a second chimeric F protein, wherein the second chimeric F protein comprises an amino acid sequence of SEQ ID NO: 22 or 39, or 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: 22 or 39; (c) a third recombinant NDV comprising a third chimeric F protein, wherein the third chimeric F protein comprises an amino acid sequence of SEQ ID NO: 6 or 18, or 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: 6 or 18; and (d) a fourth recombinant NDV comprising a fourth chimeric F protein, wherein the fourth chimeric F protein comprises an amino acid sequence of SEQ ID NO: 28 or 41, or 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: 28 or 41.

[0029] In some embodiments, the recombinant NDV described herein is inactivated. In some embodiments, the recombinant NDV described herein is live. In some embodiments, the immunogenic compositions described herein further comprise an adjuvant.

[0030] In another aspect, the recombinant NDV described herein and the immunogenic compositions described herein are for use in inducing an immune response against SARS-CoV-2, immunizing a subject, and / or preventing COVID-19. In some embodiments, provided herein is a method of inducing an immune response against SARS-CoV-2 spike protein, the method comprising administering to a subject an immunogenic composition described herein. In some embodiments, provided herein is a method of preventing COVID-19, the method comprising administering to a subject an immunogenic composition described herein. In some embodiments, provided herein is a method of immunizing a subject against SARS-CoV-2, the method comprising administering to a subject an immunogenic composition described herein. In some embodiments, provided herein is a method of immunizing a subject against two or more SARS-CoV-2, the method comprising administering to a subject an immunogenic composition described herein. In some embodiments, provided herein are methods for immunizing a subject against one or more SARS-CoV-2, the one or more SARS-CoV-2 being heterologous to the SARS-CoV-2 from which an extracellular domain of a chimeric F protein included in an immunogenic composition described herein is derived, the method comprising administering the immunogenic composition to the subject. In some embodiments, provided herein are methods for inducing antibodies that neutralize one or more SARS-CoV-2 in a subject, the one or more SARS-CoV-2 being heterologous to the SARS-CoV-2 from which an extracellular domain of a chimeric F protein included in an immunogenic composition described herein is derived, the method comprising administering the immunogenic composition to the subject. In some embodiments, provided herein are methods of inducing antibodies in a subject that cross-react with one or more SARS-CoV-2 spike proteins that are heterologous to the SARS-CoV-2 spike protein from which the extracellular domain included in an immunogenic composition described herein is derived, the method comprising administering the immunogenic composition to the subject.In certain embodiments, the composition is administered intranasally or intramuscularly to the subject. In certain embodiments, the subject is a human. In some embodiments, the subject has previously been vaccinated with a COVID-19 vaccine. In some embodiments, the subject is administered at least one booster dose of the immunogenic composition.

[0031] In another aspect, provided herein is a kit comprising the immunogenic composition described herein.

[0032] 3.1 Terminology As used herein, the term "about" or "approximately" when used in conjunction with a numerical value refers to any numerical value within 1, 5, or 10% of the referenced numerical value inclusive of the referenced numerical value.

[0033] As used herein, the term "antibody" refers to a molecule that contains an antigen-binding site, such as, for example, an immunoglobulin. Antibodies include, but are not limited to, monoclonal antibodies, bispecific antibodies, multispecific antibodies, human antibodies, humanized antibodies, synthetic antibodies, chimeric antibodies, polyclonal antibodies, single domain antibodies, camelid antibodies, single chain Fvs (scFvs), single chain antibodies, Fab fragments, F(ab') fragments, disulfide-linked bispecific Fvs (sdFvs), intrabodies and anti-idiotypic (anti-Id) antibodies (including, for example, anti-Ids and anti-Id antibodies against antibodies), as well as epitope-binding fragments of any of the foregoing. In particular, antibodies include immunoglobulin molecules and immunologically active fragments of immunoglobulin molecules. Immunoglobulin molecules may be of any type (e.g., IgG, IgE, IgM, IgD, IgA, and IgY), class (e.g., IgG1, IgG2, IgG3, IgG4, IgA1, and IgA2), or subclass.

[0034] As used herein, the term "elderly" refers to humans aged 65 and older.

[0035] As used herein, the term "adult human" refers to a human who is 18 years of age or older.

[0036] As used herein, the term "human child" refers to a human between the ages of 1 and 18 years.

[0037] As used herein, the term "human infant" refers to a human between the ages of 1 and 3.

[0038] As used herein, the term "human infant" refers to a human between the ages of newborn and 1 year.

[0039] As used herein, the phrase "IFN-deficient system" or "IFN-deficient substrate" refers to a system that does not produce one, two or more IFNs, or does not produce any type of IFN, or produces low levels of one, two or more IFNs, or produces low levels of any IFN (i.e., 5-10%, 10-20%, 20-30%, 30-40%, 40-50%, 50-60%, 60-70%, 70-80%, 80-90% or more of any IFN under the same conditions compared to a system capable of producing IFN). "IFN-inducible" refers to cells, cell lines and animal systems, such as mouse, chicken, turkey, rabbit, rat, horse, etc., that are either:

[0040] In some embodiments, a nucleotide sequence, a nucleic acid sequence, or a polynucleotide sequence is isolated. In some embodiments, an "isolated" nucleic acid sequence, a nucleotide sequence, or a polynucleotide sequence refers to a nucleic acid molecule that is separated from other nucleic acid molecules present in the natural source of the nucleic acid. In other words, an isolated nucleic acid sequence, a nucleotide sequence, or a polynucleotide sequence may contain heterologous nucleic acids with which it is not naturally associated. In other embodiments, an "isolated" nucleic acid sequence, such as, for example, a cDNA sequence or an RNA sequence, may be substantially free of other cellular material or culture medium when produced by recombinant techniques, or may be substantially free of chemical precursors or other chemicals when chemically synthesized. The term "substantially free of cellular material" includes preparations of a nucleic acid sequence, a nucleotide sequence, or a polynucleotide sequence in which the nucleic acid sequence, the nucleotide sequence, or the polynucleotide sequence is separated from cellular components of an isolated or recombinantly produced cell. Thus, a nucleic acid sequence, nucleotide sequence or polynucleotide sequence that is substantially free of cellular material includes preparations of nucleic acid sequences, nucleotide sequences or polynucleotide sequences that have 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 sequences, nucleotide sequences or polynucleotide sequences in which culture medium is 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 sequence, nucleotide sequence or polynucleotide sequence is separated from chemical precursors or other chemicals involved in the synthesis of the nucleic acid sequence, nucleotide sequence or polynucleotide sequence. In certain embodiments, such preparations of nucleic acid sequences, nucleotide sequences or polynucleotide sequences have less than about 50%, 30%, 20%, 10%, or 5% (by dry weight) of chemical precursors or compounds other than the nucleic acid sequence, nucleotide sequence or polynucleotide sequence of interest.

[0041] As used herein, the terms "subject" or "patient" are used interchangeably. As used herein, the term "subject" refers to an animal. In some embodiments, the subject is a mammal, including non-primates (e.g., camels, donkeys, zebras, cows, horses, cats, dogs, rats, and mice) and primates (e.g., monkeys, chimpanzees, and humans). In some embodiments, the subject is a non-human mammal. In certain embodiments, the subject is a pet (e.g., a dog or cat) or a farm animal (e.g., a horse, a pig, or a cow). In certain embodiments, the subject is a human. In certain embodiments, the mammal (e.g., human) is 4-6 months old, 6-12 months old, 1-5 years old, 5-10 years old, 10-15 years old, 15-20 years old, 20-25 years old, 25-30 years old, 30-35 years old, 35-40 years old, 40-45 years old, 45-50 years old, 50-55 years old, 55-60 years old, 60-65 years old, 65-70 years old, 70-75 years old, 75-80 years old, 80-85 years old, 85-90 years old, 90-95 years old, or 95-100 years old. In certain embodiments, the subject is a non-avian animal.

[0042] As used herein, (a) the term "in combination" in the context of administering a therapeutic to a subject refers to the use of multiple therapeutics. The use of the term "in combination" does not limit the order in which the therapeutics are administered to a subject. A first therapeutic may be administered prior to, simultaneously with, or subsequent to the administration of a second therapeutic to a subject.

[0043] As used herein, the terms "SARS-CoV-2 spike protein" and "spike protein of SARS-CoV-2" include SARS-CoV-2 spike proteins known to those of skill in the art. For examples of amino acid sequences of SARS-CoV-2 spike proteins and nucleotide sequences encoding SARS-CoV-2 spike proteins, see, e.g., GenBank Accession Nos. MN908947.3, MT447160, MT44636, MT446360, MT444593, MT444529, MT370887, and MT334558. Exemplary spike proteins include domains known to those of skill in the art, including an S1 domain, a receptor binding domain, an S2 domain, a transmembrane domain, and a cytoplasmic domain. For a description of the SARS-CoV-2 spike protein (particularly the structure of the protein), see, for example, Wrapp et al., 2020, Science 367:1260-1263 and Duan et al., 2020, Front. Immunol., Vol. 11, Article 576622. The spike protein may be characterized as having a signal peptide, a receptor binding domain, an extracellular domain, an S1 domain, an S2 domain, and a transmembrane domain and an intracellular domain (or cytoplasmic domain).

[0044] As used herein, the terms "SARS-CoV-2 beta variant spike protein" and "spike protein of a SARS-CoV-2 beta variant" include spike proteins of SARS-CoV-2 beta variants known to those of skill in the art, see, e.g., GISAID accession numbers EPI_ISL_660610 and EPI_ISL_678626.

[0045] As used herein, the terms "SARS-CoV-2 delta variant spike protein" and "SARS-CoV-2 delta variant spike protein" include SARS-CoV-2 delta variant spike proteins known to those of skill in the art. For SARS-CoV-2 delta variants, see, e.g., GISAID accession numbers EPI_ISL_1740580 (hCoV-19 / England / CAMC-151FDF0 / 2021), EPI_ISL_1733902 (hCoV-19 / USA / CA-CDC-FG-021941 / 2021), EPI_ISL_1731755 (hCoV-19 / India / CG-AIIMS-Raipur-L15928 / 2021), and EPI_ISL_4634223 hCoV-19 / Spain / CT-LabRefCat-1699309 / 2021. In certain embodiments, the SARS-CoV-2 delta variant can be found in GISAID accession number EPI_ISL_4634223 (hCoV-19 / Spain / CT-LabRefCat-1699309 / 2021). In certain embodiments, the SARS-CoV-2 delta variant is of the B1.617.2 sublineage. In certain embodiments, the SARS-CoV-2 delta variant is of the AY sublineage. In certain embodiments, the SARS-CoV-2 delta variant is of the AY.4, AY.25, AY.12, AY.3, AY.9, AY.3, AY.9, AY.5, AY.6, AY.20, AY.7.1, AY.23, AY.14, AY.10, AY.7, AY.13, AY.15, AY.16, AY.19, AY.2, AY.8, AY.11, AY.1, AY.21, AY.22, AY.7.2, AY.5.1, or AY.5.2 lineage.

[0046] As used herein, the term "Wuhan strain" refers to the SARS-CoV-2 strain referred to by those skilled in the art as the Wuhan strain. See, e.g., GenBank Accession No. MN908947.3.

[0047] As used herein, the terms "SARS-CoV-2 gamma variant spike protein" and "SARS-CoV-2 gamma variant spike protein" include SARS-CoV-2 gamma variant spike proteins known to those of skill in the art, see, e.g., GISAID accession numbers EPI_ISL_792680 and EPI_ISL_804814.

[0048] As used herein, the terms "SARS-CoV-2mu variant spike protein" and "SARS-CoV-2mu variant spike protein" include SARS-CoV-2mu variant spike proteins known to those of skill in the art. For example, the SARS-CoV-2mu variant spike protein may be the B.1.621 or B.1.621.1 lineage spike protein.

[0049] As used herein, the terms "SARS-CoV-2 omicron variant spike protein" and "spike protein of a SARS-CoV-2 omicron variant" include spike proteins of SARS-CoV-2 omicron variants known to those of skill in the art. For example, a SARS-CoV-2 omicron variant may be a spike protein of a lineage of B.1.1.529, BA.1, BA.1.1, BA.2, BA.3, BA.4, or BA.5.

[0050] As used herein, the term "therapy" may refer to any protocol, method, agent, or combination thereof that can be used to treat or prevent, or vaccinate against, COVID-19. In certain embodiments, the term "therapy" refers to a recombinant NDV described herein. In other embodiments, the term "therapy" refers to an agent that is not a recombinant NDV described herein. [Brief description of the drawings]

[0051] 4. Brief description of the drawings [Figure 1A]Figures 1A and 1B. Evolution of SARS-CoV-2 and emergence of variants of concern (VOCs). (Figure 1A) Phylogenetic tree (December 15, 2019 - February 6, 2022) with 3057 genomes showing the global evolutionary relatedness of SARS-CoV-2 viruses from the ongoing COVID-19 pandemic. (Figure 1B) Timeline (December 15, 2019 - February 6, 2022) showing the global frequency of emergence of different SARS-CoV-2 virus clades. Graphs adapted from the website / nextstrain.org / ncov / gisaid / global (accessed February 5, 2022, CC-BY(28, 29)). [Figure 1B] Same as above.

[0052] [Figure 2A]Figures 2A-2D. Design, production, and characterization of NDV-HXP-S variant vaccines. (Figure 2A) Structure and design of NDV-HXP-S constructs. Different SARS-CoV-2 spike sequences were introduced between the P and M genes of the LaSota L289A NDV strain. The extracellular domain of the spike protein was connected to the transmembrane and cytoplasmic domain tails (TM / CT) of the F protein of NDV. The original polybasic cleavage site was removed by mutating RRAR to A. Stabilizing mutations in HexaPro (F817P, A892P, A899P, A942P, K986P, and V987P) were introduced. The sequence was codon-optimized for expression in mammalian hosts. The original Wuhan HXP-S sequence was aligned with the following new variant constructs: beta, gamma, and delta. Changes in the N-terminal domain (NTD), receptor binding domain (RBD), and spike 2 (S2) are shown compared to the original Wuhan HXP-S sequence. (Figure 2B) NDV-HXP-S variants were rescued by reverse genetics as previously reported (Ayllon et al., 2013, J Vis Exp. (80): 50830). Expression plasmids (NP, P, and L) required for replication and transcription of the NDV viral genome were co-transfected into cells along with full-length NDV cDNA. After 2 or 3 days, tissue culture supernatants were inoculated into 8- or 9-day-old specific pathogen-free (SPF) embryonated chicken eggs. Antigen identity was confirmed by biochemical methods and sequence analysis. Genetic stability of the recombinant viruses was assessed over multiple passages in 10-day-old SPF embryonated chicken eggs. NDV-HXP-S vaccine was inactivated with BPL and purified by sucrose cushion ultracentrifugation (Sun et al., 2021, Nat. Commun. 12:6197). (Figure 2C) Comparison of NDV-HXP-S delta virus and NDV-HXP-S delta with P681R mutation. The spike protein of NDV-HN protein was detected by Western blot using anti-spike 2B3E5 mouse monoclonal antibody and anti-HN 8H2 mouse monoclonal antibody, respectively.(Figure 2D) Protein staining of NDV-HXP-S variant vaccines separated by 4-20% SDS-PAGE. Viral proteins were visualized by Coomassie blue staining (L, S0, HN, N, P and M). The uncleaved S0 spike protein is highlighted in blue and is approximately 200 kDa in size. [Figure 2B] Same as above. [Figure 2C] Same as above. [Figure 2D] Same as above.

[0053] [Figure 3A]Figures 3A-3G. NDV-HXP-S beta and gamma induce protective antibodies against homologous infection. (Figures 3A and 3B) Study and group design. 8-10 week old female BALB / c mice were used to vaccinate with either inactivated NDV-HXP-S variant vaccine or WT NDV (negative control) at a total dose of 1 μg. Two immunizations were performed by intramuscular route (IM) on days 0 and 21. On day 44, mice were treated with Ad5-hACE2. On day 49, mice were challenged with USA-WA1 / 2020, beta (B.1.351) or gamma (P.1) strains. Two days after challenge, lungs were harvested and homogenized in 1 mL of PBS to measure titers by plaque assay on Vero E6 cells. Viral titers in lung homogenates after challenge with Wuhan, beta, or gamma (n=5) (Figure 3C). Viral titers were measured by plaque assay on Vero E6 cells and plotted as GMT in PFU / mL (detection limit was 50 PFU / mL. A titer of 25 PFU / mL was assigned to negative samples). Error bars represent geometric standard deviation. Geometric mean fold titers relative to control are shown in grey. Spike-specific serum IgG values ​​against Wuhan spike protein (n=10) (Figure 3D), beta spike protein (n=10) (Figure 3E), gamma spike protein (n=10) (Figure 3F) and delta spike protein (n=5) (Figure 3G). Antibodies in post-boost (day 43) serum samples derived from the different immunization regimens were measured by ELISA. GMT AUC was graphed. Error bars represent geometric standard deviation. Statistical differences were analyzed by ordinary one-way ANOVA corrected for Dunnett's multiple comparison test in all figures (*p<0.05, **p<0.01, ***p<0.001, ****p<0.0001). [Figure 3B] Same as above. [Figure 3C] Same as above. [Figure 3D] Same as above. [Figure 3E] Same as above. [Figure 3F] Same as above. [Figure 3G] Same as above.

[0054] [Figure 4A] Figures 4A-4D. Trivalent and quadrivalent NDV-HXP-S vaccination regimens induce protection against phylogenetically distant SARS-CoV-2 variants. (Figures 4A and 4B) Study and group design. Female BALB / c mice aged 8-10 weeks were used to vaccinate with either inactivated NDV-HXP-S variant vaccine or WT NDV (negative control) at a total dose of 1 μg. Two immunizations were performed by intramuscular route (IM) on days 0 and 21. On day 44, mice were treated with Ad5-hACE2. On day 49, mice were challenged with USA-WA1 / 2020, delta (B.1.617.2) or Mu (B.1.621) strains. Two days after challenge, lungs were harvested and homogenized in 1 mL of PBS to measure titers by plaque assay. (Fig. 4C) Viral titers after challenge (n=5). Viral titers were measured by plaque assay on Vero E6 cells for Wuhan challenge and Vero TMPRSS2 cells for Delta and Mu challenges and plotted as GMT in PFU / mL (detection limit was 50 PFU / mL. Titers of 25 PFU / mL were assigned to negative samples). Error bars represent geometric standard deviation. Statistical differences were analyzed by ordinary one-way ANOVA corrected for Dunnett's multiple comparison test. p-values ​​and geometric mean fold titers relative to control are shown in blue and grey, respectively (*p<0.05, **p<0.01, ***p<0.001, ****p<0.0001). (Fig. 4D) Panel of neutralizing activity. Post-boost pooled sera were tested in microneutralization (MNT) assays in technical duplicates against the USA-WA / 2020 strain (WT), delta (B.1.617.2), beta (B.1.351), and omicron (B.1.1.529) variants. The GMT serum dilution that inhibits infection by 50% (ID50) is plotted (detection limit was 10 and assigned to negative samples). Geometric mean fold change is added in blue. [Figure 4B]Same as above. [Figure 4C-1] Same as above. [Figure 4C-2] Same as above. [Figure 4D-1] Same as above. [Figure 4D-2] Same as above.

[0055] [Figure 5A] Figures 5A-5C. Trivalent and quadrivalent NDV-HXP-S vaccination regimens induce high titers of serum antibodies against phylogenetically distant SARS-CoV-2 variants. Heatmaps of spike-specific (Figure 5A) or RBD-specific (Figure 5B) serum IgG against spike protein variants (n=10). Antibody binding was measured in various immunization assays using Wuhan, delta, alpha, beta, gamma and omicron spikes or RBD (see Figures 6A-6C and 6D-6F for individual ELISA plots). (Figure 5C) Wuhan S2-specific serum IgG (pooled from 10 samples in triplicate). Antibodies in post-boost (day 43) serum were measured by ELISA. GMT AUC is shown. [Figure 5B] Same as above. [Figure 5C] Same as above.

[0056] [Figure 6A] Figures 6A-6C and 6D-6F. Spike-specific and RBD-specific antibody titers after multivalent vaccination. Panel of spike-specific serum IgG (Figures 6A-6C) or RBD-specific serum IgG (Figures 6D-6F) against spike variants (n=10) associated with Figures 5A and 5B, respectively. Wuhan, delta, alpha, beta, gamma and omicron spikes or RBD were used to measure antibody binding in various immunization assays. Antibodies in serum post-boost (day 43) were measured by ELISA. GMT AUC is shown. Error bars represent geometric SD. Geometric mean fold change is added in blue. [Figure 6B] Same as above. [Figure 6C]Same as above. [Figure 6D] Same as above. [Figure 6E] Same as above. [Figure 6F] Same as above.

[0057] [Figure 7A] Figures 7A-7C. Trivalent NDV-HXP-S (SARS-CoV-2) live vaccine induces broad antibody responses. Mice were vaccinated intramuscularly with trivalent NDV-HXP-S vaccine, monovalent NDV-HXP-S (ancestral) vaccine, or wild-type (WT) NDV as a negative control. Mice were administered a prime dose of trivalent vaccine, monovalent vaccine, or WT NDV intramuscularly and a boost dose intramuscularly 21 days later. Twenty-one days after the booster, mice were euthanized and blood and spleens were collected to measure serum IgG levels, as well as spike protein-specific class-switched memory B cells in the spleen. IgG levels were measured by ELISA. Spike protein-specific class-switched memory B cells in spleens were verified by flow cytometry detecting live CD3-, CD220+, CD19+, IgD-, IgM-, GL7-, CD38+, APC-S+, and PE-S+ (Figure 7A). Serum IgG against a panel of ancestral and variant RBDs, including ancestral, beta, gamma, delta, BA.1, and BA.2 RBDs, was measured (Figure 7B). Spleens from mice were harvested three weeks after the booster and verified for either ancestral S-binding or BA.1 S-binding class-switched memory B cells (swMBCs) using a tetramer-SB cell probe. The frequency of ancestral S-binding or BA.1 S-binding class-switched memory B cells was plotted (Figure 7C). [Figure 7B-1] Same as above. [Figure 7B-2] Same as above. [Figure 7C] Same as above. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0058] 5. MODE FOR CARRYING OUT THEINVENTION 5.1 Recombinant Newcastle disease viruses In one embodiment, provided herein is a transgene comprising a chimeric F protein, the chimeric F protein comprising an extracellular domain of SARS-CoV-2 or a derivative thereof, and a transmembrane domain and a cytoplasmic domain of an NDV F protein. Also provided herein is a recombinant NDV comprising a transgene encoding a chimeric F protein, the chimeric F protein comprising an extracellular domain of SARS-CoV-2 or a derivative thereof, and a transmembrane domain and a cytoplasmic domain of an NDV F protein. Also provided herein is a recombinant NDV comprising a chimeric F protein, the chimeric F protein comprising an extracellular domain of SARS-CoV-2 or a derivative thereof, and a transmembrane domain and a cytoplasmic domain of an NDV F protein. The recombinant NDV may be administered as a live or inactivated virus. In another aspect, a recombinant NDV as described herein is provided that can be used to immunize a subject (e.g., a human subject) against SARS-CoV-2 (e.g., SARS-CoV-2 delta variant, SARS-CoV-2 beta variant, SARS-CoV-2 gamma variant, or the Wuhan strain). The recombinant NDV may be administered as a live virus or an inactivated virus.

[0059] 5.1.1 NDV Newcastle disease virus (NDV) is a member of the Avulaviridae family and has been shown to infect many birds (Alexander, DJ (1988). Newcastle disease, Newcastle disease virus--an avian paramyxovirus. Kluwer Academic Publishers: Dordrecht, The Netherlands. pp 1-22). NDV possesses a negative-sense single-stranded RNA genome and does not recombine with the host genome or with other viruses (Alexander, DJ (1988). Newcastle disease, Newcastle disease virus--an avian paramyxovirus. Kluwer Academic Publishers: Dordrecht, The Netherlands. pp 1-22). The genomic RNA contains genes in the order 3'-NP-PMF-HN-L-5'. By alternative mRNAs generated by RNA editing, NDV produces two additional proteins, V and W, from the P gene. The genomic RNA also contains a leader sequence at the 3' end.

[0060] Structural elements of the virion include the viral envelope, a lipid bilayer derived from the cell membrane. A glycoprotein, hemagglutinin-neuraminidase (HN), protrudes from the envelope, allowing the virus to possess both hemagglutinin (e.g., receptor binding / fusion) and neuraminidase activities. The fusion glycoprotein (F), which also interacts with the viral membrane, is initially produced as an inactive precursor and then post-translationally cleaved to generate two disulfide-linked polypeptides. The active F protein is involved in NDV entry into host cells and promotes fusion of the viral envelope with the host cell membrane. The matrix protein (M) is involved in viral assembly and interacts with both the viral membrane as well as the nucleocapsid protein.

[0061] The major protein subunit of the nucleocapsid is the nucleocapsid protein (NP), which gives the capsid its helical symmetry. The P and L proteins are associated with the nucleocapsid. The phosphorylated phosphoprotein (P) is thought to play a role in transcriptional regulation and may also be involved in methylation, phosphorylation and polyadenylation. The L gene, which encodes an RNA-dependent RNA polymerase, is required for the synthesis of viral RNA along with the P protein. The L protein, which accounts for almost half of the coding capacity of the viral genome, is the largest viral protein and plays a key role in both transcription and replication.

[0062] Any NDV type or strain, including but not limited to naturally occurring strains, variants or mutants, mutant viruses, reassortants, and / or genetically engineered viruses, may serve as a "backbone" engineered to contain the transgenes described herein. See, e.g., Section 5.1.2 and Section 6 for examples of transgenes. In a particular embodiment, the transgenes described herein are integrated into the genome of a lentogenic NDV. In another particular embodiment, the transgenes described herein are integrated into the genome of a LaSota strain of NDV. In another embodiment, the transgenes described herein are integrated into the genome of a Hitchner B1 strain of NDV. In some embodiments, a lentogenic strain other than the Hitchner B1 strain of NDV is used as a backbone into which a nucleotide sequence may be integrated. The transgene may be integrated into the NDV genome between two transcription units (e.g., between the M and P transcription units of NDV, between the NP and P transcription units of NDV, or between the HN and L transcription units of NDV, etc.).

[0063] In certain embodiments, the NDV engineered to include the transgenes described herein is a natural strain. Specific examples of NDV strains include, but are not limited to, Hitchner B1 strain (see, e.g., GenBank No. AF309418 or NC_002617) and LaSota strain (see, e.g., GenBank No. AY845400, AF07761.1, JF950510.1, and GI No. 56799463). In certain embodiments, the NDV engineered to include the transgenes described herein is a Hitchner B1 strain. In another embodiment, the NDV engineered to include the transgenes described herein is a B1 strain identified by GenBank No. AF309418 or NC_002617. In certain embodiments, the nucleotide sequence of the Hitchner B1 genome comprises an RNA sequence that corresponds to the negative sense of the cDNA sequence described in SEQ ID NO:2. In another specific embodiment, the NDV engineered to include the transgenes described herein is a LaSota strain. In another embodiment, the NDV engineered to contain the transgene described herein is a LaSota strain identified by AY845400, AF07761.1, or JF950510.1. In a particular embodiment, the nucleotide sequence of the genome of the La Sota strain comprises an RNA sequence corresponding to the negative sense of the cDNA sequence set forth in SEQ ID NO:1. In another particular embodiment, the nucleotide sequence of the genome of the La Sota strain comprises an RNA sequence corresponding to the negative sense of the cDNA sequence set forth in SEQ ID NO:3. Those skilled in the art will understand that the RNA sequence of the NDV genome is an RNA sequence corresponding to the negative sense of the cDNA sequence encoding the NDV genome. Thus, the cDNA sequence encoding the NDV genome may be converted to a genomic RNA sequence using any program that converts a nucleotide sequence to its reverse complement (see, for example, www.bioinformatics.org / sms / rev_comp.html, www.fr33.net / seqedit.php, and DNAStar).Thus, the nucleotide sequences provided in Tables 1-4 below can be readily converted by one of skill in the art into negative-sense RNA sequences of the NDV genome.

[0064] In a particular embodiment, an NDV engineered to contain a transgene described herein comprises a genome encoding an NDV F protein, where the leucine amino acid residue at amino acid position 289 of the NDV F protein is replaced with an alanine (e.g., as described in Sergel et al., 2000, Journal of Virology 74:5101-5107). In another particular embodiment, an NDV engineered to contain a transgene described herein comprises a genome encoding an NDV F protein, where the leucine amino acid residue at amino acid position 289 of the NDV F protein (as counted in the LaSota strain F protein) is replaced with an alanine. In another particular embodiment, an NDV engineered to contain a transgene described herein comprises a nucleotide sequence encoding an NDV F protein, where the leucine at the amino acid position corresponding to amino acid residue 289 of the LaSota NDV F protein is replaced with an alanine. In another specific embodiment, the NDV engineered to contain the transgene described herein comprises a nucleotide sequence encoding an NDV F protein, where the leucine at amino acid residue 289 of the LaSota NDV F protein is replaced with an alanine. In another specific embodiment, the NDV engineered to contain the transgene described herein is a LaSota strain NDV (e.g., GenBank Accession Nos. AY845400, AF07761.1, or JF950510.1), where the LaSota strain genome encodes an NDV F protein, where the leucine amino acid residue at amino acid position 289 of the NDV F protein is replaced with an alanine. In another specific embodiment, the NDV engineered to contain a transgene described herein is a LaSota strain NDV (e.g., GenBank Accession Nos. AY845400, AF07761.1, or JF950510.1), wherein the genome of the LaSota strain comprises a nucleotide sequence encoding a LaSota NDV F protein in which the leucine at amino acid residue 289 of the NDV F protein (as counted in the LaSota strain F protein) is replaced with an alanine.In another specific embodiment, the NDV engineered to contain a transgene described herein is a Hitchner B1 strain NDV (e.g., GenBank Accession No. AF309418 or NC_002617), wherein the genome of the Hitchner B1 strain encodes an NDV F protein in which the leucine amino acid residue at amino acid position 289 of the NDV F protein (as counted in the Lasota strain F protein) is replaced with an alanine.

[0065] In some embodiments, the NDV engineered to include a transgene as described herein is a Fuller strain NDV. In certain embodiments, the genome of the NDV engineered to include a transgene as described herein is an Ulster strain genome. In some embodiments, the NDV engineered to include a transgene as described herein is a Roakin strain NDV. In certain embodiments, the NDV engineered to include a transgene as described herein is a Komarov strain NDV. In some embodiments, the NDV engineered to include a transgene as described herein is a Roakin strain NDV. In certain embodiments, the NDV engineered to include a transgene as described herein is an r73T-Rl 16 virus.

[0066] In certain embodiments, the NDV engineered to include the transgenes described herein is not pathogenic in birds when assessed by techniques known in the art. In certain embodiments, the NDV engineered to include the transgenes described herein is not pathogenic when assessed by intracranial injection of the virus into one-day-old chicks and scoring for 8 days for illness and death. In some embodiments, the NDV engineered to include the transgenes described herein has an intracranial pathogenicity index of less than 0.7, less than 0.6, less than 0.5, less than 0.4, less than 0.3, less than 0.2, or less than 0.1. In certain embodiments, the NDV engineered to include the transgenes described herein has an intracranial pathogenicity index of zero. See, for example, the OIE Terrestrial Manual 2012, Chapter 2.3.14, entitled "Newcastle Disease (Infection With Newcastle Disease Virus)" for a description of this assay, which can be found at the following website, which is incorporated by reference in its entirety: www.oie.int / fileadmin / Home / eng / Health_standards / tahm / 2.03.14_NEWCASTLE_DIS.pdf.

[0067] In certain embodiments, the NDV engineered to contain the transgenes described herein is a mesogenic strain that has been genetically engineered to be not considered pathogenic in avian species when assessed by techniques known to those of skill in the art.

[0068] In a preferred embodiment, the NDV engineered to contain the transgenes described herein is non-pathogenic in humans. In a preferred embodiment, the NDV engineered to contain the transgenes described herein is non-pathogenic in humans and birds. In a particular embodiment, the NDV engineered to contain the transgenes described herein is attenuated such that the NDV remains at least partially infectious and can replicate in vivo, but produces low titers and causes non-pathogenic, asymptomatic levels of infection (see, e.g., Khattar et al., 2009, J. Virol. 83:7779-7782). Such attenuated NDV may be particularly suitable for embodiments in which the virus is administered to a subject to serve as an immunogen, e.g., a live vaccine. The virus may be attenuated by any method known in the art. In a particular embodiment, the genome of the NDV contains sequences necessary for viral infection and replication such that progeny are produced and the level of infection is asymptomatic. In a specific embodiment, the NDV is attenuated by introducing one, two, or more mutations (eg, amino acid substitutions) into the NDV V protein.

[0069] In certain embodiments, provided herein is a nucleotide sequence comprising: (1) an NDV F transcription unit, (2) an NDV NP transcription unit, (3) an NDV P transcription unit, (4) an NDV M transcription unit, (5) an NDV HN transcription unit, (6) an NDV L transcription unit, and (7) a transgene described herein. In certain embodiments, the NDV transcription unit is a LaSota NDV transcription unit. In certain embodiments, provided herein is a nucleotide sequence comprising: (1) an NDV F transcription unit, (2) an NDV NP transcription unit, (3) an NDV P transcription unit, (4) an NDV M transcription unit, (5) an NDV HN transcription unit, (6) an NDV L transcription unit, and (7) a transgene described herein, wherein the NDV F transcription unit encodes an NDV F protein having an amino acid substitution from leucine to alanine at the amino acid residue corresponding to amino acid 289 of the Lasota NDV F protein. In another specific embodiment, provided herein is a nucleotide sequence comprising: (1) an NDV F transcription unit, (2) an NDV NP transcription unit, (3) an NDV P transcription unit, (4) an NDV M transcription unit, (5) an NDV HN transcription unit, (6) an NDV L transcription unit, and (7) a transgene as described herein, wherein the NDV F transcription unit encodes an NDV F protein having an amino acid substitution from leucine to alanine at amino acid position 289 of the Lasota NDV F protein. In a specific embodiment, the NDV transcription unit is a LaSota NDV transcription unit. In a specific embodiment, the nucleotide sequence is part of a vector (e.g., a plasmid as described in the Examples below). In a specific embodiment, the nucleotide sequence is isolated.

[0070] In a specific embodiment, provided herein is a polynucleotide sequence comprising: (1) a nucleotide sequence encoding NDV F, (2) a nucleotide sequence encoding NDV NP, (3) a nucleotide sequence encoding NDV P, (4) a nucleotide sequence encoding NDV M, (5) a nucleotide sequence encoding NDV HN, (6) a nucleotide sequence encoding NDV L, and (7) a transgene described herein. In another specific embodiment, provided herein is a polynucleotide sequence comprising: (1) a nucleotide sequence encoding NDV F, (2) a nucleotide sequence encoding NDV NP, (3) a nucleotide sequence encoding NDV P, (4) a nucleotide sequence encoding NDV M, (5) a nucleotide sequence encoding NDV HN, (6) a nucleotide sequence encoding NDV L, and (7) a transgene described herein, wherein NDV F comprises an amino acid substitution from leucine to alanine at an amino acid position corresponding to amino acid residue 289 of Lasota NDV F. In another specific embodiment, provided herein is a polynucleotide sequence comprising: (1) a nucleotide sequence encoding NDV F; (2) a nucleotide sequence encoding NDV NP; (3) a nucleotide sequence encoding NDV P; (4) a nucleotide sequence encoding NDV M; (5) a nucleotide sequence encoding NDV HN; (6) a nucleotide sequence encoding NDV L; and (7) a transgene as described herein, wherein NDV F comprises an amino acid substitution of leucine to alanine at amino acid position 289 of Lasota NDV F. In a specific embodiment, the NDV protein is a Lasota NDV protein. In another specific embodiment, provided herein is a polynucleotide sequence comprising a nucleotide sequence of an NDV genome known or described in the art (see, e.g., Section 5.1 or the Examples below; see also SEQ ID NO: 1, 2, or 3), and a transgene as described herein. In a specific embodiment, the nucleic acid sequence is part of a vector (e.g., a plasmid as described in the Examples below). In a specific embodiment, the polynucleotide sequence is isolated.

[0071] In certain embodiments, the polynucleotide sequences described herein, the nucleic acid sequences described herein, or the nucleotide sequences described herein are recombinant polynucleotide sequences described herein, recombinant nucleic acid sequences described herein, or recombinant nucleotide sequences. In certain embodiments, the polynucleotide sequences described herein, the nucleotide sequences described herein, or the nucleic acid sequences described herein may be DNA molecules (e.g., cDNA), RNA molecules (e.g., mRNA), or a combination of DNA and RNA molecules. In some embodiments, the polynucleotide sequences described herein, the nucleotide sequences described herein, or the nucleic acid sequences described herein may include analogs of DNA or RNA molecules. Such analogs can be made using nucleotide analogs, including, for example, but not limited to, inosine, methylcytosine, pseudouridine, or tritylated bases. Such analogs can also include DNA or RNA molecules that contain modified backbones that confer beneficial attributes to the molecule, such as, for example, nuclease resistance, or improved ability to cross cell membranes. The polynucleotide sequences, nucleic acid sequences, or nucleotide sequences may be single-stranded, double-stranded, may include both single-stranded and double-stranded portions, and may include triple-stranded portions. In certain embodiments, the polynucleotide sequence described herein, the nucleotide sequence described herein, or the nucleic acid sequence described herein is a single-stranded RNA of negative sense.In another particular embodiment, the polynucleotide sequence described herein, the nucleotide sequence described herein, or the nucleic acid sequence described herein is a single-stranded RNA of positive sense.In another particular embodiment, the polynucleotide sequence described herein, the nucleotide sequence described herein, or the nucleic acid sequence described herein is a cDNA.

[0072] In some embodiments, provided herein is a recombinant NDV comprising a spike protein or a portion thereof (e.g., an extracellular domain or a receptor binding domain of a SARS-CoV-2 spike protein) or a derivative thereof. In a specific embodiment, provided herein is a recombinant NDV comprising a protein comprising an extracellular domain of a SARS-CoV-2 spike protein or a derivative thereof. In another specific embodiment, provided herein is a recombinant NDV comprising a protein comprising a derivative of an extracellular domain of a SARS-CoV-2 spike protein. In another specific embodiment, provided herein is a recombinant NDV comprising a chimeric F protein comprising an extracellular domain of a SARS-CoV-2 spike protein, or a derivative thereof, and a transmembrane domain and a cytoplasmic domain of an NDV F protein. In a specific embodiment, provided herein is a recombinant NDV comprising a chimeric F protein comprising a derivative of an extracellular domain of a SARS-CoV-2 spike protein, and a transmembrane domain and a cytoplasmic domain of an NDV F protein. In some embodiments, a derivative of the SARS-CoV-2 extracellular domain comprises an amino acid sequence of SEQ ID NO: 12, 13, 16, 17, 23, 24, 29, or 30. In some embodiments, a derivative of the SARS-CoV-2 extracellular domain comprises an amino acid sequence that is 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: 12, 13, 16, 17, 23, 24, 29, or 30. In some embodiments, the extracellular domain of the spike protein of SARS-CoV-2, or a derivative thereof, is encoded by a codon-optimized nucleic acid sequence. In some embodiments, a derivative of the SARS-CoV-2 spike protein is encoded by a nucleotide sequence of SEQ ID NO: 20, 21, 26, 27, 31, 32, 35, or 36.In some embodiments, the derivative of the SARS-CoV-2 spike protein is encoded by a nucleotide sequence that is 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:20, 21, 26, 27, 31, 32, 35, or 36. In some embodiments, the transmembrane and cytoplasmic domains of the NDV F protein are those of the LaSota or Hitchner strain. In some embodiments, the transmembrane and cytoplasmic domains of the NDV F protein comprise SEQ ID NO:42. In some embodiments, the derivative of the extracellular domain of the SARS-CoV-2 spike protein and the transmembrane and cytoplasmic domains of the NDV F protein are linked by a linker (e.g., a linker described herein, such as SEQ ID NO:7) or directly linked.

[0073] In some embodiments, a recombinant NDV comprising a chimeric F protein is provided herein. In some embodiments, the chimeric F protein comprises an amino acid sequence of SEQ ID NO: 6, 11, 18, 22, 28, 39, 40, or 41. In some embodiments, the chimeric F protein comprises an amino acid sequence that is 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: 6, 11, 18, 22, 28, 39, 40, or 41. In some embodiments, the chimeric F protein is encoded by a codon-optimized nucleic acid sequence. In some embodiments, the chimeric F protein is encoded by a nucleotide sequence of SEQ ID NO: 5, 19, 25, 33, 34, 37, or 38. In some embodiments, the chimeric F protein is encoded by a nucleotide sequence that is 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:5, 19, 25, 33, 34, 37, or 38.

[0074] 5.1.2 Chimeric F proteins containing SARS-CoV-2 variant spike protein / SARS-CoV-2 variant spike protein extracellular domain or derivatives thereof In a particular embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising a SARS-CoV-2 spike protein or a portion thereof (e.g., the extracellular domain, S1 domain, S2 domain, or receptor binding domain of the SARS-CoV-2 spike protein). In another particular embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising a SARS-CoV-2 delta variant spike protein or a portion thereof (e.g., the extracellular domain, S1 domain, S2 domain, or receptor binding domain of the SARS-CoV-2 delta variant spike protein). In another particular embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising a SARS-CoV-2 beta variant spike protein or a portion thereof (e.g., the extracellular domain, S1 domain, S2 domain, or receptor binding domain of the SARS-CoV-2 beta variant spike protein). In another specific embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising a spike protein of a SARS-CoV-2 gamma variant or a portion thereof (e.g., the extracellular domain, the S1 domain, the S2 domain, or the receptor binding domain of the spike protein of a SARS-CoV-2 gamma variant). In another specific embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising a spike protein of a SARS-CoV-2 Wuhan strain or a portion thereof (e.g., the extracellular domain, the S1 domain, the S2 domain, or the receptor binding domain of the spike protein of a SARS-CoV-2 Wuhan strain).

[0075] In certain embodiments, a transgene comprising a nucleotide sequence encoding a protein comprising a spike protein of a SARS-CoV-2 delta variant or a portion thereof (e.g., the extracellular domain, S1 domain, S2 domain, or receptor binding domain of the spike protein of a SARS-CoV-2 delta variant) is integrated into the genome of any NDV type or strain (e.g., NDV Lasota strain). For types and strains of NDV that may be used, see, e.g., Section 0 above. A transgene encoding a spike protein of a SARS-CoV-2 delta variant or a portion thereof (e.g., the extracellular domain, S1 domain, S2 domain, or receptor binding domain of the spike protein of a SARS-CoV-2 delta variant) may be inserted into any NDV type or strain (e.g., NDV Lasota strain). In certain embodiments, a transgene encoding the spike protein of a SARS-CoV-2 delta variant or a portion thereof (e.g., the extracellular domain, the S1 domain, the S2 domain, or the receptor binding domain of the spike protein of a SARS-CoV-2 delta variant) is integrated into the genome of any NDV type or strain (e.g., the NDV Lasota strain). In certain embodiments, the SARS-CoV-2 delta variant is of the B1.617.2 sublineage. In certain embodiments, the SARS-CoV-2 delta variant is of the AY sublineage. See, e.g., Section 0 for exemplary sequences of SARS-CoV-2 delta variant spike proteins or portions thereof (e.g., the extracellular domain, S1 domain, S2 domain, or receptor binding domain of SARS-CoV-2 delta variant spike proteins), as well as exemplary nucleic acid sequences encoding SARS-CoV-2 delta variant spike proteins or portions thereof (e.g., the extracellular domain, S1 domain, S2 domain, or receptor binding domain of SARS-CoV-2 delta variant spike proteins). Using such sequence information, one of skill in the art would be able to generate and integrate a transgene into the genome of any NDV type or strain.Given the degeneracy of the nucleic acid code, there are many different polynucleotide sequences that can encode the same SARS-CoV-2 delta variant spike protein or portion thereof (e.g., the extracellular domain, S1 domain, S2 domain, or receptor binding domain of the SARS-CoV-2 delta variant spike protein). In certain embodiments, the transgene encoding the SARS-CoV-2 delta variant spike protein or portion thereof (e.g., the extracellular domain, S1 domain, S2 domain, or receptor binding domain of the SARS-CoV-2 delta variant spike protein) is codon optimized. See, e.g., Section 5.1.4 below for a discussion regarding codon optimization. In certain embodiments, the transgene encoding the SARS-CoV-2 delta variant spike protein or portion thereof (e.g., the extracellular domain, S1 domain, S2 domain, or receptor binding domain of the SARS-CoV-2 delta variant spike protein) does not include the signal peptide of the SARS-CoV-2 delta variant spike protein. A transgene encoding the spike protein of a SARS-CoV-2 delta variant or a portion thereof (e.g., the extracellular domain, the S1 domain, the S2 domain, or the receptor binding domain of the spike protein of a SARS-CoV-2 delta variant) may be incorporated into any two NDV transcription units (e.g., between the NDV P transcription unit and the NDV M transcription unit, between the NDV NP transcription unit and the NDV P transcription unit, or between the HN transcription unit and the L transcription unit).

[0076] In another specific embodiment, a transgene comprising a nucleotide sequence encoding a protein comprising a spike protein of a SARS-CoV-2 beta variant or a portion thereof (e.g., the extracellular domain, S1 domain, S2 domain, or receptor binding domain of the spike protein of a SARS-CoV-2 beta variant) is integrated into the genome of any NDV type or strain (e.g., NDV Lasota strain). For types and strains of NDV that may be used, see, e.g., Section 0 above. A transgene encoding a spike protein of a SARS-CoV-2 beta variant or a portion thereof (e.g., the extracellular domain, S1 domain, S2 domain, or receptor binding domain of the spike protein of a SARS-CoV-2 beta variant) may be inserted into any NDV type or strain (e.g., NDV Lasota strain). In certain embodiments, a transgene encoding a spike protein or a portion thereof (e.g., the extracellular domain, S1 domain, S2 domain, or receptor binding domain of a spike protein of a SARS-CoV-2 beta variant) of a SARS-CoV-2 beta variant is integrated into the genome of any NDV type or strain (e.g., NDV Lasota strain). In certain embodiments, the SARS-CoV-2 beta variant is the B.1.351 lineage, or a derived lineage thereof. See, e.g., Section 0, for exemplary sequences of a spike protein or a portion thereof (e.g., the extracellular domain, S1 domain, S2 domain, or receptor binding domain of a spike protein of a SARS-CoV-2 beta variant), as well as exemplary polynucleotide sequences encoding a spike protein or a portion thereof (e.g., the extracellular domain, S1 domain, S2 domain, or receptor binding domain of a spike protein of a SARS-CoV-2 beta variant). Using such sequence information, one of skill in the art would be able to generate and integrate a transgene into the genome of any NDV type or strain.Given the degeneracy of the nucleic acid code, there are many different polynucleotide sequences that can encode the same SARS-CoV-2 beta variant spike protein or portion thereof (e.g., the extracellular domain, S1 domain, S2 domain, or receptor binding domain of the SARS-CoV-2 beta variant spike protein). In certain embodiments, the transgene encoding the SARS-CoV-2 beta variant spike protein or portion thereof (e.g., the extracellular domain, S1 domain, S2 domain, or receptor binding domain of the SARS-CoV-2 beta variant spike protein) is codon optimized. See, e.g., Section 5.1.4 below for a discussion regarding codon optimization. In certain embodiments, the transgene encoding the SARS-CoV-2 beta variant spike protein or portion thereof (e.g., the extracellular domain, S1 domain, S2 domain, or receptor binding domain of the SARS-CoV-2 beta variant spike protein) does not include the signal peptide of the SARS-CoV-2 beta variant spike protein. A transgene encoding the spike protein of a SARS-CoV-2 beta variant or a portion thereof (e.g., the extracellular domain, the S1 domain, the S2 domain, or the receptor binding domain of the spike protein of a SARS-CoV-2 beta variant) may be incorporated into any two NDV transcription units (e.g., between the NDV P transcription unit and the NDV M transcription unit, between the NDV NP transcription unit and the NDV P transcription unit, or between the HN transcription unit and the L transcription unit).

[0077] In another specific embodiment, a transgene comprising a nucleotide sequence encoding a protein comprising a spike protein of a SARS-CoV-2 gamma variant or a portion thereof (e.g., the extracellular domain, S1 domain, S2 domain, or receptor binding domain of the spike protein of a SARS-CoV-2 gamma variant) is integrated into the genome of any NDV type or strain (e.g., NDV Lasota strain). A transgene encoding a spike protein of a SARS-CoV-2 gamma variant or a portion thereof (e.g., the extracellular domain, S1 domain, S2 domain, or receptor binding domain of the spike protein of a SARS-CoV-2 gamma variant) may be inserted into any NDV type or strain (e.g., NDV Lasota strain). In certain embodiments, a transgene encoding the spike protein of a SARS-CoV-2 gamma variant or a portion thereof (e.g., the extracellular domain, S1 domain, S2 domain, or receptor binding domain of the spike protein of a SARS-CoV-2 gamma variant) is integrated into the genome of any NDV type or strain (e.g., NDV Lasota strain). In certain embodiments, the SARS-CoV-2 gamma variant is the P.1 lineage or a derivative thereof, or a lineage described in Section 6. See, e.g., Section 3.1 for exemplary sequences of SARS-CoV-2 gamma variant spike proteins or portions thereof (e.g., the extracellular domain, S1 domain, S2 domain, or receptor binding domain of SARS-CoV-2 gamma variant spike proteins), as well as exemplary polynucleotide sequences encoding SARS-CoV-2 gamma variant spike proteins or portions thereof (e.g., the extracellular domain, S1 domain, S2 domain, or receptor binding domain of SARS-CoV-2 gamma variant spike proteins). Using such sequence information, one of skill in the art would be able to generate and integrate a transgene into the genome of any NDV type or strain.Given the degeneracy of the nucleic acid code, there are many different polynucleotide sequences that can encode the same SARS-CoV-2 gamma variant spike protein or portion thereof (e.g., the extracellular domain, S1 domain, S2 domain, or receptor binding domain of the SARS-CoV-2 gamma variant spike protein). In certain embodiments, the transgene encoding the SARS-CoV-2 gamma variant spike protein or portion thereof (e.g., the extracellular domain, S1 domain, S2 domain, or receptor binding domain of the SARS-CoV-2 gamma variant spike protein) is codon optimized. See, e.g., Section 5.1.4 below for a discussion regarding codon optimization. In certain embodiments, the transgene encoding the SARS-CoV-2 gamma variant spike protein or portion thereof (e.g., the extracellular domain, S1 domain, S2 domain, or receptor binding domain of the SARS-CoV-2 gamma variant spike protein) does not include the signal peptide of the SARS-CoV-2 gamma variant spike protein. A transgene encoding the SARS-CoV-2 gamma variant spike protein or a portion thereof (e.g., the extracellular domain, the S1 domain, the S2 domain, or the receptor binding domain of the SARS-CoV-2 gamma variant spike protein) may be incorporated into any two NDV transcription units (e.g., between the NDV P and NDV M transcription units, between the NDV NP and NDV P transcription units, or between the HN and L transcription units).

[0078] In another specific embodiment, a transgene comprising a nucleotide sequence encoding a protein comprising the SARS-CoV-2 Wuhan spike protein or a portion thereof (e.g., the extracellular domain, S1 domain, S2 domain, or receptor binding domain of the SARS-CoV-2 Wuhan spike protein) is integrated into the genome of any NDV type or strain (e.g., NDV Lasota strain). A transgene encoding the SARS-CoV-2 Wuhan strain spike protein or a portion thereof (e.g., the extracellular domain, S1 domain, S2 domain, or receptor binding domain of the SARS-CoV-2 Wuhan strain spike protein) may be inserted into any NDV type or strain (e.g., NDV Lasota strain). In certain embodiments, a transgene encoding the spike protein of the Wuhan strain of SARS-CoV-2 or a portion thereof (e.g., the extracellular domain, S1 domain, S2 domain, or receptor binding domain of the spike protein of the Wuhan strain of SARS-CoV-2) is integrated into the genome of any NDV type or strain (e.g., NDV Lasota strain). Using such sequence information, a person skilled in the art would be able to generate and integrate a transgene into the genome of any NDV type or strain. Given the degeneracy of the nucleic acid code, there are many different polynucleotide sequences that can encode the same spike protein of the Wuhan strain of SARS-CoV-2 or a portion thereof (e.g., the extracellular domain, S1 domain, S2 domain, or receptor binding domain of the spike protein of the Wuhan strain of SARS-CoV-2). In certain embodiments, a transgene encoding the spike protein of the Wuhan strain of SARS-CoV-2 or a portion thereof (e.g., the extracellular domain, the S1 domain, the S2 domain, or the receptor binding domain of the spike protein of the Wuhan strain of SARS-CoV-2) is codon-optimized. See, e.g., Section 5.1.4 below for a discussion regarding codon optimization.In certain embodiments, the transgene encoding the spike protein of the Wuhan strain of SARS-CoV-2 or a portion thereof (e.g., the extracellular domain, the S1 domain, the S2 domain, or the receptor binding domain of the spike protein of the Wuhan strain of SARS-CoV-2) does not include the signal peptide of the spike protein of the Wuhan strain of SARS-CoV-2. The transgene encoding the spike protein of the Wuhan strain of SARS-CoV-2 or a portion thereof (e.g., the extracellular domain, the S1 domain, the S2 domain, or the receptor binding domain of the spike protein of the Wuhan strain of SARS-CoV-2) may be integrated into any two NDV transcription units (e.g., between the NDV P transcription unit and the NDV M transcription unit, between the NDV NP transcription unit and the NDV P transcription unit, or between the HN transcription unit and the L transcription unit).

[0079] In certain embodiments, the portion of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) comprises a receptor binding domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant). In certain embodiments, the portion of the spike protein of SARS-CoV-2 comprises a receptor binding domain of a SARS-CoV-2 protein. In some embodiments, the portion of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) comprises a receptor binding domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), as well as 5, 10, 15, 20, 30, 40, 50, 75, or more amino acid residues N-terminal to the receptor binding domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), or a portion of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) that is 5, 10, 15, 20, 30, 40, 50, 75, or more amino acid residues N-terminal to the receptor binding domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant). ant), or 5, 10, 15, 20, 30, 40, 50, 75, or more amino acid residues N-terminal to the receptor binding domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), and 5, 10, 15, 20, 30, 40, 50, 75, or more amino acid residues C-terminal to the receptor binding domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant).In some embodiments, the portion of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) comprises a receptor binding domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), as well as 5-25, 5-50, 25-50, 25-75, or 50-75 amino acid residues N-terminal to the receptor binding domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), or 5-25, 5-50, 25-50, 25-75, or 50-75 amino acid residues N-terminal to the receptor binding domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), and 5-25, 5-50, 25-50, 25-75, or 50-75 amino acid residues C-terminal to the receptor binding domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant). In certain embodiments, the spike protein of SARS-CoV-2 is the spike protein of a SARS-CoV-2 delta variant. In another specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of a SARS-CoV-2 beta variant. In another specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of a SARS-CoV-2 gamma variant. In another specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of the SARS-CoV-2 Wuhan strain.

[0080] In certain embodiments, the portion of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) includes the S1 domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant). In some embodiments, the portion of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) comprises an S1 domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), as well as 5, 10, 15, 20, 30, 40, 50, 75, or more amino acid residues N-terminal to the S1 domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), or a portion of the S1 domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant). or 5, 10, 15, 20, 30, 40, 50, 75 or more amino acid residues N-terminal to the S1 domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), and 5, 10, 15, 20, 30, 40, 50, 75 or more amino acid residues C-terminal to the S1 domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant).In some embodiments, the portion of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) comprises an S1 domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), as well as 5-25, 5-50, 25-50, 25-75, or 50-75 amino acid residues N-terminal to the S1 domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), ant), or 5-25, 5-50, 25-50, 25-75, or 50-75 amino acid residues N-terminal to the S1 domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), and 5-25, 5-50, 25-50, 25-75, or 50-75 amino acid residues C-terminal to the S1 domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant). In certain embodiments, the spike protein of SARS-CoV-2 is the spike protein of a SARS-CoV-2 delta variant. In another specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of a SARS-CoV-2 beta variant. In another specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of a SARS-CoV-2 gamma variant. In another specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of the SARS-CoV-2 Wuhan strain.

[0081] In certain embodiments, the portion of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) includes the S2 domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant). In some embodiments, the portion of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) comprises an S2 domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), as well as 5, 10, 15, 20, 30, 40, 50, 75, or more amino acid residues N-terminal to the S2 domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), or a portion of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) that is 5, 10, 15, 20, 30, 40, 50, 75, or more amino acid residues N-terminal to the S2 domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant). or 5, 10, 15, 20, 30, 40, 50, 75 or more amino acid residues N-terminal to the S2 domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), and 5, 10, 15, 20, 30, 40, 50, 75 or more amino acid residues C-terminal to the S2 domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant).In some embodiments, the portion of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) comprises an S2 domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), as well as 5-25, 5-50, 25-50, 25-75, or 50-75 amino acid residues N-terminal to the S2 domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), Ant), or 5-25, 5-50, 25-50, 25-75, or 50-75 amino acid residues N-terminal to the S2 domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), and 5-25, 5-50, 25-50, 25-75, or 50-75 amino acid residues C-terminal to the S2 domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant). In certain embodiments, the spike protein of SARS-CoV-2 is the spike protein of a SARS-CoV-2 delta variant. In another specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of a SARS-CoV-2 beta variant. In another specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of a SARS-CoV-2 gamma variant. In another specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of the SARS-CoV-2 Wuhan strain.

[0082] In certain embodiments, the portion of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) includes the S1 domain and the S2 domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant). In some embodiments, the portion of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) comprises the S1 domain and S2 domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) and 5, 10, 15, 20, 30, 40, 50, 75, or more amino acid residues N-terminal to the S1 domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), or or 5, 10, 15, 20, 30, 40, 50, 75 or more amino acid residues C-terminal to the S2 domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), or 5, 10, 15, 20, 30, 40, 50, 75 or more amino acid residues N-terminal to the S1 domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), and 5, 10, 15, 20, 30, 40, 50, 75 or more amino acid residues C-terminal to the S2 domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant).In some embodiments, the portion of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) comprises the S1 domain and S2 domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), and 5-25, 5-50, 25-50, 25-75, or 50-75 amino acid residues N-terminal to the S1 domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant). The spike protein of SARS-CoV-2 may comprise 5-25, 5-50, 25-50, 25-75, or 50-75 amino acid residues C-terminal to the S2 domain, or 5-25, 5-50, 25-50, 25-75, or 50-75 amino acid residues N-terminal to the S1 domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), and 5-25, 5-50, 25-50, 25-75, or 50-75 amino acid residues C-terminal to the S2 domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant). In certain embodiments, the spike protein of SARS-CoV-2 is the spike protein of SARS-CoV-2 delta variant. In another specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of a SARS-CoV-2 beta variant. In another specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of a SARS-CoV-2 gamma variant. In another specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of the SARS-CoV-2 Wuhan strain.

[0083] In certain embodiments, the portion of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) includes the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant). In some embodiments, the portion of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) can be an extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), as well as 5, 10, 15, 20, 30, 40, 50, 75, or more amino acid residues relative to the N-terminus of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), or a portion of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant). or 5, 10, 15, 20, 30, 40, 50, 75 or more amino acid residues N-terminal to the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), and 5, 10, 15, 20, 30, 40, 50, 75 or more amino acid residues C-terminal to the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant).In some embodiments, the portion of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) comprises an extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), as well as 5-25, 5-50, 25-50, 25-75, or 50-75 amino acid residues N-terminal to the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), or 5-25, 5-50, 25-50, 25-75, or 50-75 amino acid residues N-terminal to the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), and 5-25, 5-50, 25-50, 25-75, or 50-75 amino acid residues C-terminal to the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant). In certain embodiments, the spike protein of SARS-CoV-2 is the spike protein of a SARS-CoV-2 delta variant. In another specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of a SARS-CoV-2 beta variant. In another specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of a SARS-CoV-2 gamma variant. In another specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of the SARS-CoV-2 Wuhan strain.

[0084] In certain embodiments, the portion of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) comprises 200, 220, 222, 250, 300, 350, 400, or more amino acid residues. In some embodiments, the portion of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) comprises 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1100, 1200, or more. In certain embodiments, the spike protein of SARS-CoV-2 is the spike protein of a SARS-CoV-2 delta variant. In another specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of a SARS-CoV-2 beta variant. In another specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of the SARS-CoV-2 gamma variant. In another specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of the SARS-CoV-2 Wuhan strain.

[0085] In another embodiment, described herein is a transgene comprising a nucleotide sequence encoding a full-length SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) spike protein or a fragment thereof. In certain embodiments, the protein further comprises a domain that facilitates purification, folding, and cleavage of a portion of the polypeptide. For example, a His tag (His-His-His-His-His-His (SEQ ID NO: 44)), a FLAG epitope, or other purification tag can facilitate purification of the proteins provided herein. In some embodiments, the His tag has the sequence (His)n, where n is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more. In certain embodiments, the fragment of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) is at least 1000, 1025, 1075, 1100, 1125, 1150, 1200, or 1215 amino acid residues in length. In certain embodiments, the spike protein of SARS-CoV-2 is the spike protein of SARS-CoV-2 delta variant. In another specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of SARS-CoV-2 beta variant. In another specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of SARS-CoV-2 gamma variant. In another specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of SARS-CoV-2 Wuhan strain. In some embodiments, the SARS-CoV-2 is of the B1.617.2 sublineage. In some embodiments, the SARS-CoV-2 is of the AY sublineage.

[0086] In another embodiment, provided herein is a transgene comprising a nucleotide sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to the nucleotide sequence of the spike protein or a portion thereof (e.g., the extracellular domain, the S1 domain, the S2 domain, or the receptor binding domain), or a fragment thereof, of SAR-CoV-2 (e.g., the Wuhan strain, the delta variant, the beta variant, or the gamma variant). In another embodiment, provided herein is a transgene comprising a nucleotide sequence that is at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to the nucleotide sequence of the spike protein or a portion thereof (e.g., the extracellular domain, the S1 domain, the S2 domain, or the receptor binding domain), or a fragment thereof, of SAR-CoV-2 (e.g., the Wuhan strain, the delta variant, the beta variant, or the gamma variant). In another embodiment, provided herein is a transgene comprising a nucleotide sequence that is at least 96%, at least 97%, at least 98%, or at least 99% identical to the nucleotide sequence of the spike protein or a portion thereof (e.g., the extracellular domain, the S1 domain, the S2 domain, or the receptor binding domain), or a fragment thereof, of SARS-CoV-2 (e.g., the Wuhan strain, delta variant, beta variant, or gamma variant). In a specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of a SARS-CoV-2 delta variant. In another specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of a SARS-CoV-2 beta variant. In another specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of a SARS-CoV-2 gamma variant. In another specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of a SARS-CoV-2 Wuhan strain.Sequence identity may be determined using methods / techniques known in the art (see, e.g., the "Best Fit" or "Gap" programs of the Sequence Analysis Software Package, version 10, Genetics Computer Group, Inc.). In certain embodiments, the protein further comprises one or more polypeptide domains. The one or more polypeptide domains may be at the C-terminus, or the N-terminus, or the C-terminus and the N-terminus. In certain embodiments, the one or more polypeptide domains are at the C-terminus. Useful polypeptide domains include domains that facilitate purification, folding, and cleavage of the polypeptide moiety. For example, a His tag (His-His-His-His-His-His (SEQ ID NO: 44)), a FLAG epitope, or other purification tags can facilitate purification of the proteins provided herein. In some embodiments, the His tag has the sequence (His)n, where n is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more. In one embodiment, the His tag has the sequence (His)n, where n is 6 (SEQ ID NO:44). In certain embodiments, the fragment of the SARS-CoV-2 spike protein is at least 250, at least 500, at least 750, at least 1000, at least 1025, at least 1075, at least 1100, at least 1125, at least 1150, at least 1175, at least 1200, or at least 1215 amino acid residues in length.

[0087] Techniques known to those skilled in the art can be used to determine the percent identity between two amino acid sequences or the percent identity between two nucleotide sequences. In general, to determine the percent identity between two amino acid sequences or two nucleic acid sequences, the sequences are aligned for optimal comparison purposes (e.g., gaps can be introduced in the sequence of the first amino acid sequence or nucleic acid sequence for optimal alignment with the second amino acid sequence or nucleic acid sequence). The amino acid residues or nucleotides at the corresponding amino acid positions or nucleotide positions are then compared. If a position in the first sequence is occupied by the same amino acid residue or nucleotide as the corresponding position in the second sequence, the molecules are identical at that position. The percent identity between two sequences is a function of the number of identical positions shared by the sequences (i.e., percent identity%=number of overlapping positions that are identical / total number of positionsX100%). In one embodiment, the two sequences are the same length. In certain embodiments, the percent identity is determined over the entire length of the amino acid sequence or nucleotide sequence. In some embodiments, the length of sequence identity comparison can be over the entire length of the two sequences being compared (e.g., the entire length of a gene coding sequence, or a fragment thereof). In some embodiments, a fragment of a nucleotide sequence is at least 25, at least 50, at least 75, or at least 100 nucleotides. Similarly, the "percent sequence identity" of an amino acid sequence over the entire length of a protein or a fragment thereof can be easily determined. In some embodiments, a fragment of a protein comprises at least 20, at least 30, at least 40, at least 50, or more consecutive amino acids of the protein. In certain embodiments, a fragment of a protein comprises at least 75, at least 100, at least 125, at least 150, or more consecutive amino acids of the protein.In some embodiments, a fragment of a protein comprises at least 175, at least 200, at least 300, at least 400, at least 500, at least 600, at least 700, at least 800, at least 900, at least 1000, at least 1100, at least 1200, or at least 1250, at least 1300, or more consecutive amino acids of the protein. In some embodiments, a fragment of a protein comprises between 100 and 1300 consecutive amino acids, between 100 and 1250 consecutive amino acids, between 100 and 1100 consecutive amino acids, between 100 and 1000 consecutive amino acids, between 500 and 1300 consecutive amino acids, between 500 and 1250 consecutive amino acids, between 500 and 1100 consecutive amino acids, or between 500 and 100 consecutive amino acids of the protein. In some embodiments, a fragment of a protein comprises 50-500 contiguous amino acids, 50-250 contiguous amino acids, 100-500 contiguous amino acids, 200-500 contiguous amino acids, 100-400 contiguous amino acids, 100-300 contiguous amino acids, 200-400 contiguous amino acids, 100-200 contiguous amino acids, or 200-300 contiguous amino acids of the protein.

[0088] The percent identity between two sequences (e.g., amino acid sequences or nucleic acid sequences) can be determined using a mathematical algorithm.A preferred non-limiting example of the mathematical algorithm used to compare two sequences is the modified version of the algorithm of Karlin and Altschul, 1990, Proc.Natl.Acad.Sci.USA 87:2264 2268, Karlin and Altschul, 1993, Proc.Natl.Acad.Sci.USA 90:5873 5877.Such an algorithm is incorporated into the NBLAST and XBLAST programs of Altschul et al., 1990, J.Mol.Biol.215:403.For example, the parameters of the NBLAST nucleotide program can be set to score 100 and word length 12 to perform BLAST nucleotide search and obtain the nucleotide sequence homologous to the nucleic acid molecule described herein. For example, BLAST protein search can be performed using the parameters of XBLAST program, such as score 50 and word length 3, to obtain amino acid sequences homologous to the protein molecules described herein. Gapped BLAST can be used to obtain gapped alignments and comparisons as described in Altschul et al., 1997, Nucleic Acids Res. 25:3389 3402. Alternatively, PSI BLAST can be used to perform an iterative search to detect distant relationships between molecules (ibid.). When using BLAST, Gapped BLAST, and PSI Blast programs, the default parameters of each program (e.g., XBLAST and NBLAST) can be used (see, e.g., National Center for Biotechnology Information (NCBI), ncbi.nlm.nih.gov on the World Wide Web). Another preferred, non-limiting example of a mathematical algorithm used to compare sequences is the algorithm of Myers and Miller, 1988, CABIOS 4:11 17.Such an algorithm is incorporated into 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 PAM120 weight residue table, a gap length penalty of 12, and a gap penalty of 4 can be used.

[0089] 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.

[0090] In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein that comprises (or consists of) the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) in which 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or more amino acids have been replaced with another amino acid (e.g., conservative amino acid substitutions). In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein that comprises (or consists of) the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) in which 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids at the C-terminus have been replaced with another amino acid (e.g., conservative amino acid substitutions). In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) in which 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids at the N-terminus have been replaced with another amino acid (e.g., conservative amino acid substitution). In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) a spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) in which 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids at the N-terminus have been replaced with another amino acid (e.g., conservative amino acid substitutions) and 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids at the C-terminus have been replaced with another amino acid (e.g., conservative amino acid substitutions). In a particular embodiment, the N-terminus is the first 100 amino acid residues of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant).In certain embodiments, the C-terminus is the last 100 amino acid residues of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant). In certain embodiments, the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) is the mature form of the protein. In other embodiments, the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) is the non-mature form of the protein. In certain embodiments, the spike protein of SARS-CoV-2 is the spike protein of SARS-CoV-2 delta variant. In another specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of SARS-CoV-2 beta variant. In another specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of SARS-CoV-2 gamma variant. In another particular embodiment, the spike protein of SARS-CoV-2 is the spike protein of the Wuhan strain of SARS-CoV-2. Examples of conservative amino acid substitutions include, for example, replacing one class of amino acid with another amino acid of the same class. In certain embodiments, conservative substitutions do not change the structure or function, or both, of the polypeptide. Classes of amino acids include hydrophobic (Met, Ala, Val, Leu, Ile), neutral hydrophilic (Cys, Ser, Thr), acidic (Asp, Glu), basic (Asn, Gln, His, Lys, Arg), conformation disruptors (Gly, Pro), and aromatic (Trp, Tyr, Phe). In certain embodiments, the protein further comprises one or more polypeptide domains. The one or more polypeptide domains may be at the C-terminus or N-terminus. In certain embodiments, the one or more polypeptide domains are at the C-terminus. Useful polypeptide domains include domains that facilitate purification, folding, and cleavage of the polypeptide moiety.For example, a His tag (His-His-His-His-His-His (SEQ ID NO: 44)), a FLAG epitope, or other purification tag can facilitate purification of the proteins provided herein. In some embodiments, the His tag has the sequence (His)n, where n is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more. In one embodiment, the His tag has the sequence (His)n, where n is 6 (SEQ ID NO: 44).

[0091] In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) having 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids deleted. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) having 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids deleted from the C-terminus. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) a spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) with 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids deleted from the N-terminus. In certain embodiments, the N-terminus is the first 100 amino acid residues of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant). In certain embodiments, the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) is the mature form of the protein. In other embodiments, the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) is a non-mature form of the protein. In certain embodiments, the spike protein of SARS-CoV-2 is the spike protein of a SARS-CoV-2 delta variant.In another specific embodiment, the spike protein of SARS-CoV-2 is a spike protein of a SARS-CoV-2 beta variant. In another specific embodiment, the spike protein of SARS-CoV-2 is a spike protein of a SARS-CoV-2 gamma variant. In another specific embodiment, the spike protein of SARS-CoV-2 is a spike protein of a SARS-CoV-2 Wuhan strain. In certain embodiments, the protein further comprises one or more polypeptide domains. The one or more polypeptide domains may be at the C-terminus or N-terminus. In certain embodiments, the one or more polypeptide domains are at the C-terminus. Useful polypeptide domains include domains that facilitate purification, folding, and cleavage of the polypeptide moiety. For example, a His tag (His-His-His-His-His-His (SEQ ID NO: 44)), a FLAG epitope, or other purification tags can facilitate purification of the proteins provided herein. In some embodiments, the His tag has the sequence (His)n, where n is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more. In one embodiment, the His tag has the sequence (His)n, where n is 6 (SEQ ID NO:44).

[0092] In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) the spike protein of SARS-CoV-2 (e.g., the Wuhan strain, delta variant, beta variant, or gamma variant) having one, two, three, four, five, six, seven, eight, nine, ten, eleven, twelve, thirteen, fourteen, fifteen, sixteen, seventeen, eighteen, nineteen, twenty, or more mutations (e.g., amino acid substitutions, amino acid deletions, amino acid additions, or combinations thereof). In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) a spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) with 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acid deletions and 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acid substitutions. In some embodiments, the mutations (e.g., amino acid substitutions, amino acid deletions, amino acid additions, or combinations thereof) are at the N-terminus, C-terminus, or both. In certain embodiments, the N-terminus is the first 100 amino acid residues of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant). In certain embodiments, the C-terminus is the last 100 amino acid residues of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant). In certain embodiments, the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) is the mature form of the protein. In other embodiments, the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) is the non-mature form of the protein. In certain embodiments, the spike protein of SARS-CoV-2 is the spike protein of SARS-CoV-2 delta variant. In another specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of SARS-CoV-2 beta variant.In another specific embodiment, the spike protein of SARS-CoV-2 is a spike protein of SARS-CoV-2 gamma variant. In another specific embodiment, the spike protein of SARS-CoV-2 is a spike protein of SARS-CoV-2 Wuhan strain. In certain embodiments, the protein further comprises one or more polypeptide domains. The one or more polypeptide domains may be at the C-terminus, the N-terminus, or the C-terminus and the N-terminus. In certain embodiments, the one or more polypeptide domains are at the C-terminus. Useful polypeptide domains include domains that facilitate purification, folding, and cleavage of the polypeptide moiety. For example, a His tag (His-His-His-His-His-His (SEQ ID NO: 44)), a FLAG epitope, or other purification tags can facilitate purification of the proteins provided herein. In some embodiments, the His tag has the sequence (His)n, where n is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more. In one embodiment, the His tag has the sequence (His)n, where n is 6 (SEQ ID NO:44).

[0093] In another embodiment, described herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) a receptor binding domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant). In a particular embodiment, the spike protein of SARS-CoV-2 is the spike protein of SARS-CoV-2 delta variant. In another particular embodiment, the spike protein of SARS-CoV-2 is the spike protein of SARS-CoV-2 beta variant. In another particular embodiment, the spike protein of SARS-CoV-2 is the spike protein of SARS-CoV-2 gamma variant. In another particular embodiment, the spike protein of SARS-CoV-2 is the spike protein of SARS-CoV-2 Wuhan strain. In a particular embodiment, the protein further comprises one or more polypeptide domains. Useful polypeptide domains include domains that facilitate purification, folding, and cleavage of the polypeptide moiety. For example, a His tag (His-His-His-His-His-His (SEQ ID NO: 44)), a FLAG epitope, or other purification tag can facilitate purification of the proteins provided herein. In some embodiments, the His tag has the sequence (His)n, where n is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more. In certain embodiments, the protein comprises or consists of the receptor binding domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) and a His tag (e.g., (His)n, where n is 6 (SEQ ID NO: 44)). In certain embodiments, the protein comprising (or consisting of) the receptor binding domain of the spike polypeptide / protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) is a secreted polypeptide.In certain embodiments, when designing a protein that includes the receptor binding domain of the spike polypeptide / protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), care should be taken to maintain the stability of the resulting protein. Additionally, in some embodiments, when designing a protein that includes the extracellular domain of the spike protein of SARS-CoV-2 or a derivative thereof, care should be taken to maintain the conformation of the spike protein so that it can bind, for example, to human angiotensin-converting enzyme-2.

[0094] In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) a receptor binding domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) in which 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids have been replaced with another amino acid (e.g., conservative amino acid substitutions). In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) a receptor binding domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) in which 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids at the C-terminus of the receptor binding domain have been replaced with another amino acid (e.g., conservative amino acid substitutions). In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) a receptor binding domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), in which 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids at the N-terminus of the receptor binding domain have been replaced with another amino acid (e.g., a conservative amino acid substitution). In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) a receptor binding domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), in which 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids at the N-terminus of the receptor binding domain have been replaced with another amino acid (e.g., conservative amino acid substitution), and 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids at the C-terminus of the receptor binding domain have been replaced with another amino acid (e.g., conservative amino acid substitution).In certain embodiments, the N-terminus is the first 25 amino acid residues of the receptor binding domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant). In certain embodiments, the C-terminus is the last 25 amino acid residues of the receptor binding domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant). In certain embodiments, the spike protein of SARS-CoV-2 is the spike protein of SARS-CoV-2 delta variant. In another specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of SARS-CoV-2 beta variant. In another specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of SARS-CoV-2 gamma variant. In another specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of SARS-CoV-2 Wuhan strain. Examples of conservative amino acid substitutions include, for example, replacing an amino acid of one class with another amino acid of the same class. In certain embodiments, conservative substitutions do not change the structure or function, or both, of the polypeptide. Classes of amino acids include hydrophobic (Met, Ala, Val, Leu, Ile), neutral hydrophilic (Cys, Ser, Thr), acidic (Asp, Glu), basic (Asn, Gln, His, Lys, Arg), conformation disruptors (Gly, Pro), and aromatic (Trp, Tyr, Phe). In certain embodiments, the protein further comprises one or more polypeptide domains. The one or more polypeptide domains may be at the C-terminus, the N-terminus, or the C-terminus and the N-terminus. In certain embodiments, the one or more polypeptide domains are at the C-terminus. Useful polypeptide domains include domains that facilitate purification, folding, and cleavage of the polypeptide moiety. For example, a His tag (His-His-His-His-His-His (SEQ ID NO:44)), a FLAG epitope, or other purification tag, can facilitate purification of the proteins provided herein.In some embodiments, the His tag has the sequence (His)n, where n is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more. In one embodiment, the His tag has the sequence (His)n, where n is 6 (SEQ ID NO:44).

[0095] In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) a receptor binding domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) having 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids deleted from the C-terminus of the receptor binding domain. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) a receptor binding domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) having 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids deleted from the N-terminus of the receptor binding domain. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) a receptor binding domain of a spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) with 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids deleted from the N-terminus of the receptor binding domain and 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids deleted from the C-terminus of the receptor binding domain. In certain embodiments, the N-terminus is the first 25 amino acid residues of the receptor binding domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant). In certain embodiments, the C-terminus is the last 25 amino acid residues of the receptor binding domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant). In a specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of the SARS-CoV-2 delta variant. In another specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of the SARS-CoV-2 beta variant.In another specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of SARS-CoV-2 gamma variant. In another specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of SARS-CoV-2 Wuhan strain. In certain embodiments, the protein further comprises one or more polypeptide domains. The one or more polypeptide domains may be at the C-terminus or N-terminus. In certain embodiments, the one or more polypeptide domains are at the C-terminus. Useful polypeptide domains include domains that facilitate purification, folding, and cleavage of the polypeptide moiety. For example, a His tag (His-His-His-His-His-His (SEQ ID NO: 44)), a FLAG epitope, or other purification tags can facilitate purification of the proteins provided herein. In some embodiments, the His tag has the sequence (His)n, where n is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more. In one embodiment, the His tag has the sequence (His)n, where n is 6 (SEQ ID NO:44).

[0096] In another embodiment, described herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) an extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant). In another embodiment, described herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) a derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant). In certain embodiments, described herein is a transgene that includes a nucleotide sequence encoding a protein that includes (or consists of) a derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), where the derivative lacks the polybasic cleavage site of the extracellular domain (e.g., one, two, or more residues corresponding to amino acid residues 682-685 (RRAR) of GenBank Accession No. MN908947.3 are replaced with other amino acid residues). In certain embodiments, the amino acid residues corresponding to amino acid residues 682-685 (RRAR) of GenBank Accession No. MN908947.3 are replaced with an alanine. In another embodiment, described herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) comprising amino acid substitutions to proline at amino acid residues corresponding to amino acid residues 817, 892, 899, 942, 986, and 987.In another embodiment, described herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) an extracellular domain of the spike protein of SARS-CoV-2 (e.g., the Wuhan strain, delta variant, beta variant, or gamma variant), in which amino acid residues corresponding to amino acid residues 682-685 (RRAR) of GenBank Accession No. MN908947.3 are substituted with an alanine, and amino acid substitutions to proline at amino acid residues corresponding to amino acid residues 817, 892, 899, 942, 986, and 987. In some embodiments, a derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) comprises the amino acid sequence of SEQ ID NO: 12, including one, two, three, four, five, six, seven, eight, or all of the following amino acid modifications: T19R, G142D, delE156, delF157, R158G, L452R, T478K, D614G, P681R, and D950N. In certain embodiments, a derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) does not include the amino acid substitution P681R. In certain embodiments, a derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) comprises the amino acid sequence of SEQ ID NO: 12, including one, two, three, four, five, six, seven, or all of the following amino acid modifications: T19R, G142D, delE156, delF157, R158G, L452R, T478K, D614G, and D950N. In certain embodiments, a derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) comprises the amino acid sequence of SEQ ID NO: 12, including the following amino acid modifications: T19R, G142D, delE156, delF157, R158G, L452R, T478K, D614G, and D950N.In another embodiment, a derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) comprises the amino acid sequence of SEQ ID NO: 12, including one, two, three, four, five, six, seven, eight, nine, ten, eleven, twelve, thirteen, fourteen, or all of the following amino acid modifications: T19R, G142D, delE156, delF157, R158G, A222V, W258L, K417N, L452R, T478K, D614G, P681R, and D950N. In a particular embodiment, a derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) does not include the amino acid substitution P681R. In some embodiments, a derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) comprises the amino acid sequence of SEQ ID NO: 12, including one, two, three, four, five, six, seven, eight, nine, ten, eleven, twelve, thirteen, or all of the following amino acid modifications: T19R, G142D, delE156, delF157, R158G, A222V, W258L, K417N, L452R, T478K, D614G, and D950N. In certain embodiments, a derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) comprises the amino acid sequence of SEQ ID NO: 12, containing the following amino acid modifications: T19R, G142D, delE156, delF157, R158G, A222V, W258L, K417N, L452R, T478K, D614G, and D950N. In some embodiments, a derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) comprises the amino acid sequence of SEQ ID NO: 16, including one, two, three, four, five, six, seven, eight, or all of the following amino acid modifications: T6R, G129D, delE143, delF144, R145G, L439R, T465K, D601G, and D937N.In some embodiments, a derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) comprises the amino acid sequence of SEQ ID NO: 12, including one, two, three, four, five, six, seven, eight, nine or more, or all of the following amino acid modifications: L18F, D80A, L246del, L247del, E484K, N501Y, D614G, and A701V. In some embodiments, a derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) comprises the amino acid sequence of SEQ ID NO: 12, including one, two, three, four, five, six, seven, eight, nine or more, or all of the following amino acid modifications: L19R, G142D, G157del, G158del, L452R, T478K, D614G, and D950N. In some embodiments, a derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) comprises the amino acid sequence of SEQ ID NO: 12, including one, two, three, four, five, six, seven, eight, nine or more, or all of the following amino acid modifications: L18F, T20N, P26S, D138Y, R190S, K417T, E484K, N501Y, D614N, H655Y, and T1027I. In certain embodiments, the protein further comprises one or more polypeptide domains. Useful polypeptide domains include domains that facilitate purification, folding, and cleavage of the polypeptide moiety. For example, a His tag (His-His-His-His-His-His (SEQ ID NO: 44)), a FLAG epitope, or other purification tags can facilitate purification of the proteins provided herein. In some embodiments, the His tag has the sequence (His)n, where n is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more.In certain embodiments, the protein comprises or consists of the extracellular domain of the SARS-CoV-2 spike protein and a His tag (e.g., (His)n, where n is 6 (SEQ ID NO:44)). In certain embodiments, the protein comprising (or consisting of) the extracellular domain of the SARS-CoV-2 spike polypeptide, or a derivative thereof, is a secreted polypeptide. In certain embodiments, the protein comprises the extracellular domain of the SARS-CoV-2 spike polypeptide, or a derivative thereof, and includes one or more trimerization domains known to those of skill in the art (e.g., a T4 foldon trimerization domain), and optionally a tag (e.g., a His tag or a Flag tag). In certain embodiments, when designing a protein comprising the extracellular domain of the SARS-CoV-2 spike polypeptide, or a derivative thereof, care should be taken to maintain the stability of the resulting protein.

[0097] In some embodiments, described herein is a transgene comprising a polynucleotide sequence encoding a derivative of the extracellular domain of the spike protein of SARS-CoV-2, wherein the polynucleotide sequence comprises a nucleotide sequence at least 80%, at least 85%, or at least 90% identical to the nucleotide sequence of SEQ ID NO: 20, 21, 26, 27, 31, 32, 35, or 36. In some embodiments, described herein is a transgene comprising a polynucleotide sequence encoding a derivative of the extracellular domain of the spike protein of SARS-CoV-2, wherein the polynucleotide sequence comprises a nucleotide sequence at least 95%, at least 98%, or at least 99% identical to the nucleotide sequence of SEQ ID NO: 20, 21, 26, 27, 31, 32, 35, or 36. In some embodiments, described herein is a transgene comprising a polynucleotide sequence encoding a derivative of the extracellular domain of the spike protein of SARS-CoV-2, wherein the polynucleotide sequence comprises the nucleotide sequence of SEQ ID NO: 20, 21, 26, 27, 31, 32, 35, or 36.

[0098] In some embodiments, described herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) a derivative of the extracellular domain of the spike protein of SARS-CoV-2, where the amino acid residue corresponding to amino acid residues 682-685 (RRAR) of GenBank Accession No. MN908947.3 is replaced with an alanine. In some embodiments, described herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) a derivative of the extracellular domain of the spike protein of SARS-CoV-2, where the amino acid residue corresponding to amino acid residues 682-685 (RRAR) of GenBank Accession No. MN908947.3 is replaced with an alanine. and the amino acid sequence of GenBank Accession No. MN908947.3, in which amino acid residues corresponding to 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or 21 of the following positions of 947.3 are substituted: 18, 19, 20, 26, 80, 138, 142, 156, 190, 215, 246, 417, 452, 478, 484, 501, 614, 655, 701, 950 and 1027.In some embodiments, described herein is a transgene comprising a nucleotide sequence encoding a protein that comprises (or consists of) a derivative of the extracellular domain of the spike protein of SARS-CoV-2, wherein the derivative (i) has an amino acid residue corresponding to amino acid residues 682-685 (RRAR) of GenBank Accession No. MN908947.3 substituted with a single alanine, and (ii) has amino acid substitutions corresponding to the following substituted amino acid residues of GenBank Accession No. MN908947.3: F817P, A892P, A8 and (iii) amino acid changes corresponding to 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or 21 of the following positions in GenBank Accession No. MN908947.3: 18, 19, 20, 26, 80, 138, 142, 156, 190, 215, 246, 417, 452, 478, 484, 501, 614, 655, 701, 950 and 1027.

[0099] In some embodiments, described herein is a transgene comprising a nucleotide sequence encoding a protein that comprises (or consists of) a derivative of the extracellular domain of the spike protein of SARS-CoV-2, wherein the derivative has (i) an amino acid residue corresponding to amino acid residues 682 to 685 (RRAR) of GenBank Accession No. MN908947.3 substituted with a single alanine, and (ii) an amino acid residue corresponding to the following residues of GenBank Accession No. MN908947.3: and (iii) amino acid changes corresponding to one, two, three, four, five, six, seven, eight or all of the following: L18F, D80A, L242del, A243del, L244del, R246I, K417N, E484K, N501Y, D614G, and A701V. In some embodiments, a derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises the amino acid sequence of SEQ ID NO: 12, comprising one, two, three, four, five, six, seven, eight or all of the following amino acid changes: L18F, D80A, L242del, A243del, L244del, R246I, K417N, E484K, N501Y, D614G and A701V.

[0100] In some embodiments, described herein is a transgene comprising a nucleotide sequence encoding a protein that comprises (or consists of) a derivative of the extracellular domain of the spike protein of SARS-CoV-2, wherein the derivative has (i) an amino acid residue corresponding to amino acid residues 682 to 685 (RRAR) of GenBank Accession No. MN908947.3 substituted with a single alanine; and (iii) amino acid substitutions corresponding to one, two, three, four, five, six, seven, eight, nine, ten or all of the following: L18F, T20N, P26S, D138Y, R190S, K417T, E484K, N501Y, D614N, H655Y, and T1027I. In some embodiments, a derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises the amino acid sequence of SEQ ID NO: 12, comprising one, two, three, four, five, six, seven, eight, nine, ten or all of the following amino acid substitutions: L18F, T20N, P26S, D138Y, R190S, K417T, E484K, N501Y, D614N, H655Y, and T1027I.

[0101] In some embodiments, described herein is a transgene comprising a nucleotide sequence encoding a protein that comprises (or consists of) a derivative of the extracellular domain of the spike protein of SARS-CoV-2, wherein the derivative has (i) an amino acid residue corresponding to amino acid residues 682 to 685 (RRAR) of GenBank Accession No. MN908947.3 substituted with a single alanine; and (ii) an amino acid residue corresponding to amino acid residues 682 to 685 (RRAR) of GenBank Accession No. MN908947.3 substituted with a single alanine. and (iii) amino acid changes corresponding to one, two, three, four, five, six, seven, eight or all of the following: L19R, G142D, G157del, G158del, L452R, T478K, D614G, and D950N. In some embodiments, a derivative of the extracellular domain of the spike protein of SARS-CoV-2 comprises the amino acid sequence of SEQ ID NO: 12, comprising one, two, three, four, five, six, seven, eight or all of the following amino acid substitutions: L19R, G142D, G157del, G158del, L452R, T478K, D614G, and D950N.

[0102] In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) an extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) in which 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids have been replaced with another amino acid (e.g., conservative amino acid substitutions). In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) an extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) in which 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids have been replaced with another amino acid (e.g., conservative amino acid substitutions) at the C-terminus of the extracellular domain. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), wherein 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids at the N-terminus of the extracellular domain have been replaced with another amino acid (e.g., conservative amino acid substitution). In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) an extracellular domain of a spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), with 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids substituted with another amino acid (e.g., conservative amino acid substitution) at the N-terminus of the extracellular domain and 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids substituted with another amino acid (e.g., conservative amino acid substitution) at the C-terminus of the extracellular domain. In certain embodiments, the C-terminus of the extracellular domain is the last 100 amino acid residues. In certain embodiments, the N-terminus of the extracellular domain is the first 100 amino acid residues.In certain embodiments, the spike protein of SARS-CoV-2 is the spike protein of a SARS-CoV-2 delta variant. In another particular embodiment, the spike protein of SARS-CoV-2 is the spike protein of a SARS-CoV-2 beta variant. In another particular embodiment, the spike protein of SARS-CoV-2 is the spike protein of a SARS-CoV-2 gamma variant. In another particular embodiment, the spike protein of SARS-CoV-2 is the spike protein of a SARS-CoV-2 Wuhan strain. Examples of conservative amino acid substitutions include, for example, replacing an amino acid of one class with another amino acid of the same class. In certain embodiments, conservative substitutions do not alter the structure or function, or both, of the polypeptide. Amino acid classes include hydrophobic (Met, Ala, Val, Leu, Ile), neutral hydrophilic (Cys, Ser, Thr), acidic (Asp, Glu), basic (Asn, Gln, His, Lys, Arg), conformation disruptor (Gly, Pro), and aromatic (Trp, Tyr, Phe). In certain embodiments, the protein further comprises one or more polypeptide domains. The one or more polypeptide domains may be at the C-terminus, the N-terminus, or the C-terminus and the N-terminus. In certain embodiments, the one or more polypeptide domains are at the C-terminus. Useful polypeptide domains include domains that facilitate purification, folding, and cleavage of the polypeptide moiety. For example, a His tag (His-His-His-His-His-His (SEQ ID NO: 44)), a FLAG epitope, or other purification tags can facilitate purification of the proteins provided herein. In some embodiments, the His tag has the sequence (His)n, where n is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more. In one embodiment, the His tag has the sequence (His)n, where n is 6 (SEQ ID NO:44).In certain embodiments, the protein comprising (or consisting of) the extracellular domain of a SARS-CoV-2 delta variant spike protein (e.g., a SARS-CoV-2 delta variant spike polypeptide / protein) is a secreted polypeptide. In certain embodiments, the protein comprises the extracellular domain of a SARS-CoV-2 delta variant spike protein (e.g., a SARS-CoV-2 delta variant spike polypeptide / protein) and includes one or more trimerization domains known to those of skill in the art (e.g., a T4 foldon trimerization domain), and optionally a tag (e.g., a His tag or a Flag tag).

[0103] In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) an amino acid sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 13. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) an amino acid sequence that is at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 13. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) the amino acid sequence of SEQ ID NO: 13. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) the amino acid sequence of SEQ ID NO: 13 minus the signal peptide. For signal peptide, see SEQ ID NO: 15. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) an amino acid sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 17. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) an amino acid sequence that is at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 17. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) the amino acid sequence of SEQ ID NO: 17. In certain embodiments, the protein further comprises one or more polypeptide domains. The one or more polypeptide domains may be at the C-terminus, the N-terminus, or at the C-terminus and the N-terminus.In certain embodiments, one or more polypeptide domains are at the C-terminus. Useful polypeptide domains include domains that facilitate purification, folding, and cleavage of the polypeptide moiety. For example, a His tag (His-His-His-His-His-His (SEQ ID NO: 44)), a FLAG epitope, or other purification tag can facilitate purification of the proteins provided herein. In some embodiments, the His tag has the sequence (His)n, where n is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more. In one embodiment, the His tag has the sequence (His)n, where n is 6 (SEQ ID NO: 44). In certain embodiments, the protein is a secreted polypeptide. In some embodiments, the protein further comprises the transmembrane and cytoplasmic domains of the NDV F protein. In some embodiments, the protein further comprises one or more trimerization domains known to those of skill in the art (eg, a T4 foldon trimerization domain), and optionally a tag (eg, a His tag or a Flag tag).

[0104] In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) an amino acid sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 12. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) an amino acid sequence that is at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 12. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) the amino acid sequence of SEQ ID NO: 12. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) the amino acid sequence of SEQ ID NO: 12 minus the signal peptide. For signal peptide, see SEQ ID NO: 15. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) an amino acid sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 16. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) an amino acid sequence that is at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 16. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) the amino acid sequence of SEQ ID NO: 16. In certain embodiments, the protein further comprises one or more polypeptide domains. The one or more polypeptide domains may be at the C-terminus, the N-terminus, or the C-terminus and the N-terminus.In certain embodiments, one or more polypeptide domains are at the C-terminus. Useful polypeptide domains include domains that facilitate purification, folding, and cleavage of the polypeptide moiety. For example, a His tag (His-His-His-His-His-His (SEQ ID NO: 44)), a FLAG epitope, or other purification tag can facilitate purification of the proteins provided herein. In some embodiments, the His tag has the sequence (His)n, where n is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more. In one embodiment, the His tag has the sequence (His)n, where n is 6 (SEQ ID NO: 44). In certain embodiments, the protein is a secreted polypeptide. In some embodiments, the protein further comprises the transmembrane and cytoplasmic domains of the NDV F protein. In some embodiments, the protein further comprises one or more trimerization domains known to those of skill in the art (eg, a T4 foldon trimerization domain), and optionally a tag (eg, a His tag or a Flag tag).

[0105] In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) an amino acid sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 23. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) an amino acid sequence that is at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 23. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) the amino acid sequence of SEQ ID NO: 23. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) the amino acid sequence of SEQ ID NO: 23 minus the signal peptide. For signal peptide, see SEQ ID NO: 15. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) an amino acid sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 24. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) an amino acid sequence that is at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 24. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) the amino acid sequence of SEQ ID NO: 24. In certain embodiments, the protein further comprises one or more polypeptide domains. The one or more polypeptide domains may be at the C-terminus, the N-terminus, or the C-terminus and the N-terminus.In certain embodiments, one or more polypeptide domains are at the C-terminus. Useful polypeptide domains include domains that facilitate purification, folding, and cleavage of the polypeptide moiety. For example, a His tag (His-His-His-His-His-His (SEQ ID NO: 44)), a FLAG epitope, or other purification tag can facilitate purification of the proteins provided herein. In some embodiments, the His tag has the sequence (His)n, where n is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more. In one embodiment, the His tag has the sequence (His)n, where n is 6 (SEQ ID NO: 44). In certain embodiments, the protein is a secreted polypeptide. In some embodiments, the protein further comprises the transmembrane and cytoplasmic domains of the NDV F protein. In some embodiments, the protein further comprises one or more trimerization domains known to those of skill in the art (eg, a T4 foldon trimerization domain), and optionally a tag (eg, a His tag or a Flag tag).

[0106] In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) an amino acid sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 29. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) an amino acid sequence that is at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 29. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) the amino acid sequence of SEQ ID NO: 29. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) the amino acid sequence of SEQ ID NO: 29 minus the signal peptide. For signal peptide, see SEQ ID NO: 15. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) an amino acid sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 30. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) an amino acid sequence that is at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 30. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) the amino acid sequence of SEQ ID NO: 30. In certain embodiments, the protein further comprises one or more polypeptide domains. The one or more polypeptide domains may be at the C-terminus, the N-terminus, or at the C-terminus and the N-terminus.In certain embodiments, one or more polypeptide domains are at the C-terminus. Useful polypeptide domains include domains that facilitate purification, folding, and cleavage of the polypeptide moiety. For example, a His tag (His-His-His-His-His-His (SEQ ID NO: 44)), a FLAG epitope, or other purification tag can facilitate purification of the proteins provided herein. In some embodiments, the His tag has the sequence (His)n, where n is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more. In one embodiment, the His tag has the sequence (His)n, where n is 6 (SEQ ID NO: 44). In certain embodiments, the protein is a secreted polypeptide. In some embodiments, the protein further comprises the transmembrane and cytoplasmic domains of the NDV F protein. In some embodiments, the protein further comprises one or more trimerization domains known to those of skill in the art (eg, a T4 foldon trimerization domain), and optionally a tag (eg, a His tag or a Flag tag).

[0107] In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) comprising 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acid substitutions and with 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acid deletions. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) with 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids deleted from the C-terminus. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) an extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) having 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids deleted from the N-terminus. In certain embodiments, the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) lacks a polybasic cleavage site (e.g., amino acid residues 682-685 (RRAR) are replaced with an alanine). In some embodiments, the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) contains the following amino acid substitutions at amino acid residues that correspond to amino acid residues in GenBank Accession No. MN908947.3: F817P, A892P, A899P, A942P, K986P, and V987P.In certain embodiments, the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) comprises one alanine amino acid substitution at amino acid residues corresponding to amino acid residues 682-685 (RRAR) of GenBank Accession No. MN908947.3, and the following amino acid substitutions at amino acid residues corresponding to amino acid residues of GenBank Accession No. MN908947.3: F817P, A892P, A899P, A942P, K986P, and V987P. In certain embodiments, the C-terminus of the extracellular domain is the last 100 amino acid residues. In certain embodiments, the N-terminus of the extracellular domain is the first 100 amino acid residues. In certain embodiments, the spike protein of SARS-CoV-2 is a spike protein of a SARS-CoV-2 delta variant. In another specific embodiment, the spike protein of SARS-CoV-2 is a spike protein of a SARS-CoV-2 beta variant. In another specific embodiment, the spike protein of SARS-CoV-2 is a spike protein of a SARS-CoV-2 gamma variant. In another specific embodiment, the spike protein of SARS-CoV-2 is a spike protein of a SARS-CoV-2 Wuhan strain. In certain embodiments, the protein further comprises one or more polypeptide domains. The one or more polypeptide domains may be at the C-terminus, the N-terminus, or the C-terminus and the N-terminus. In certain embodiments, the one or more polypeptide domains are at the C-terminus. Useful polypeptide domains include domains that facilitate purification, folding, and cleavage of the polypeptide moiety. For example, a His tag (His-His-His-His-His-His (SEQ ID NO: 44)), a FLAG epitope, or other purification tags can facilitate purification of the proteins provided herein. In some embodiments, the His tag has the sequence (His)n, where n is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more.In one embodiment, the His tag has the sequence (His)n, where n is 6 (SEQ ID NO:44). In some embodiments, the protein further comprises the transmembrane and cytoplasmic domains of the NDV F protein. In some embodiments, the protein comprising the extracellular domain of the spike polypeptide of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) further comprises one or more trimerization domains known to those of skill in the art (e.g., T4 foldon trimerization domain), and optionally a tag (e.g., a His tag or a Flag tag).

[0108] In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) having 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids deleted from the C-terminus. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) having 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids deleted from the C-terminus. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) an extracellular domain of a spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) having 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids deleted from the N-terminus. In certain embodiments, the extracellular domain of the spike protein of a delta variant of SARS-CoV-2 lacks a polybasic cleavage site (e.g., one, two, or more residues corresponding to amino acid residues 682-685 (RRAR) of GenBank Accession No. MN908947.3 are replaced with other amino acid residues). In certain embodiments, the amino acid residues corresponding to amino acid residues 682-685 (RRAR) of GenBank Accession No. MN908947.3 are replaced with an alanine. In some embodiments, amino acid substitutions corresponding to the following amino acid residues in GenBank Accession No. MN908947.3 are substituted: F817P, A892P, A899P, A942P, K986P, and V987P. In certain embodiments, the spike protein of SARS-CoV-2 is the spike protein of the SARS-CoV-2 delta variant.In another specific embodiment, the spike protein of SARS-CoV-2 is a spike protein of a SARS-CoV-2 beta variant. In another specific embodiment, the spike protein of SARS-CoV-2 is a spike protein of a SARS-CoV-2 gamma variant. In another specific embodiment, the spike protein of SARS-CoV-2 is a spike protein of a SARS-CoV-2 Wuhan strain. In certain embodiments, the protein further comprises one or more polypeptide domains. The one or more polypeptide domains may be at the C-terminus, the N-terminus, or the C-terminus and the N-terminus. In certain embodiments, the one or more polypeptide domains are at the C-terminus. Useful polypeptide domains include domains that facilitate purification, folding, and cleavage of the polypeptide moiety. For example, a His tag (His-His-His-His-His-His (SEQ ID NO: 44)), a FLAG epitope, or other purification tags can facilitate purification of the proteins provided herein. In some embodiments, the His tag has the sequence (His)n, where n is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more. In one embodiment, the His tag has the sequence (His)n, where n is 6 (SEQ ID NO: 44). In some embodiments, the protein further comprises a transmembrane domain and a cytoplasmic domain of an NDV F protein. In certain embodiments, the protein comprising the extracellular domain of the spike polypeptide of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) comprises one or more trimerization domains known to those of skill in the art (e.g., T4-foldon trimerization domain), and optionally a tag (e.g., a His tag or a Flag tag).

[0109] In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) an extracellular domain of a spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) having 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 mutations (e.g., amino acid substitutions, amino acid deletions, amino acid additions, or combinations thereof). In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) an extracellular domain of a spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) having 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acid substitutions and having 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acid deletions. In certain embodiments, the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) lacks a polybasic cleavage site (e.g., one, two, or more residues corresponding to amino acid residues 682-685 (RRAR) of GenBank Accession No. MN908947.3 are replaced with other amino acid residues). In certain embodiments, the amino acid residues corresponding to amino acid residues 682-685 (RRAR) of GenBank Accession No. MN908947.3 are replaced with an alanine. In some embodiments, amino acid substitutions corresponding to the following amino acid residues of GenBank Accession No. MN908947.3 are replaced: F817P, A892P, A899P, A942P, K986P, and V987P. In certain embodiments, the spike protein of SARS-CoV-2 is a spike protein of a SARS-CoV-2 delta variant. In another specific embodiment, the spike protein of SARS-CoV-2 is the spike protein of the SARS-CoV-2 beta variant.In another specific embodiment, the spike protein of SARS-CoV-2 is a spike protein of SARS-CoV-2 gamma variant. In another specific embodiment, the spike protein of SARS-CoV-2 is a spike protein of SARS-CoV-2 Wuhan strain. In certain embodiments, the protein further comprises one or more polypeptide domains. The one or more polypeptide domains may be at the C-terminus, the N-terminus, or the C-terminus and the N-terminus. In certain embodiments, the one or more polypeptide domains are at the C-terminus. Useful polypeptide domains include domains that facilitate purification, folding, and cleavage of the polypeptide moiety. For example, a His tag (His-His-His-His-His-His (SEQ ID NO: 44)), a FLAG epitope, or other purification tags can facilitate purification of the proteins provided herein. In some embodiments, the His tag has the sequence (His)n, where n is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more. In some embodiments, the protein further comprises a transmembrane domain and a cytoplasmic domain of an NDV F protein. In certain embodiments, the protein comprising the extracellular domain of the spike polypeptide of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) comprises one or more trimerization domains known to those of skill in the art (e.g., T4 foldon trimerization domain), and optionally a tag (e.g., His tag or Flag tag).

[0110] In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein, wherein the protein comprises an extracellular domain of a spike protein that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 12, 13, 23, or 29. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein, wherein the protein comprises an extracellular domain of a spike protein that is at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 12, 13, 23, or 29. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein, wherein the protein comprises an extracellular domain of a spike protein that is at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 12, 13, 23, or 29. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein, wherein the protein comprises an extracellular domain of a spike protein that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 12, 13, 23, or 29, without the signal sequence. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein, wherein the protein comprises an extracellular domain of a spike protein that is at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 12, 13, 23, or 29, without the signal sequence.In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein, wherein the protein comprises an extracellular domain of a spike protein that is at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 12, 13, 23, or 29, not including the signal sequence. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein, wherein the protein comprises an extracellular domain of a spike protein that is at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 16, 17, 24, or 30. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein, wherein the protein comprises an extracellular domain of a spike protein that is at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 16, 17, 24, or 30. Sequence identity may be determined using methods / techniques known in the art (see, for example, the "Best Fit" or "Gap" programs of the Sequence Analysis Software Package, Version 10, Genetics Computer Group, Inc.).

[0111] In another embodiment, the extracellular domain of the SARS-CoV-2 spike protein or a derivative thereof comprises an amino acid sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 12, 13, 16, 17, 23, 24, 29, or 30. In another embodiment, the extracellular domain of the SARS-CoV-2 spike protein or a derivative thereof comprises an amino acid sequence that is at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 12, 13, 16, 17, 23, 24, 29, or 30. In another embodiment, the extracellular domain of the SARS-CoV-2 spike protein or derivative thereof comprises an amino acid sequence that is at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the nucleotide sequence of SEQ ID NO: 12, 13, 16, 17, 23, 24, 29, or 30. In another embodiment, provided herein is an extracellular domain of the SARS-CoV-2 spike protein or derivative thereof, comprising an amino acid sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 12, 13, 23, or 29, without the signal sequence. In another embodiment, the extracellular domain of the spike protein of the SARS-CoV-2 delta variant or a derivative thereof comprises an amino acid sequence that is at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 12, 13, 23, or 29, without the signal sequence.In another embodiment, the extracellular domain of the spike protein of the SARS-CoV-2 delta variant or a derivative thereof comprises an amino acid sequence that is at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 12, 13, 23, or 29, not including the signal sequence. Sequence identity may be determined using methods / techniques known in the art (see, for example, the "Best Fit" or "Gap" programs of the Sequence Analysis Software Package, version 10, Genetics Computer Group, Inc.).

[0112] In another embodiment, described herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein, wherein the chimeric F protein comprises an extracellular domain of a spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) as described herein, and a transmembrane domain and a cytoplasmic domain of an NDV F protein. In certain embodiments, the entire transmembrane domain and a cytoplasmic domain of an NDV F protein are included in the chimeric F protein. In certain embodiments, the transmembrane domain and a cytoplasmic domain of an NDV F protein comprise the amino acid sequence of SEQ ID NO: 42. In some embodiments, the NDV F protein is included in the chimeric F protein, rather than the entire transmembrane domain and a cytoplasmic domain of the NDV F protein. In some embodiments, the entire transmembrane domain and a cytoplasmic domain of the NDV F protein are not included in the chimeric F protein. For example, several amino acid residues (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 1-5, 1-10, or 5-15 amino acid residues) upstream of the transmembrane domain of the NDV F protein may be included in the chimeric F protein, and / or several amino acid residues (e.g., 1-5, 1-10, or 5-15 amino acid residues) downstream of the cytoplasmic domain of the NDV F protein may be included in the chimeric F protein. For example, several amino acid residues (e.g., 1, 2, 3, 4, 5, or 1-5 amino acid residues) smaller than the entire transmembrane domain of the NDV F protein may be included in the chimeric F protein, and / or several amino acid residues (e.g., 1, 2, 3, 4, 5, or 1-5 amino acid residues) smaller than the entire cytoplasmic domain of the NDV F protein may be included in the chimeric F protein.In certain embodiments, described herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein, wherein the chimeric F protein comprises the extracellular domain of the SARS-CoV-2 spike protein described herein, the transmembrane domain of the NDV F protein + / - 1, 2, 3, 4, or 5 amino acid residues, and the cytoplasmic domain of the NDV F protein + / - 1, 2, 3, 4, or 5 amino acid residues. In certain embodiments, the entire transmembrane and cytoplasmic domains of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) are not present in the chimeric F protein. In some embodiments, 1, 2, or 3 amino acid residues of the transmembrane and / or cytoplasmic domains of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) are present in the chimeric F protein. The extracellular, transmembrane and cytoplasmic domains of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) and the NDV F protein may be determined using techniques known to those skilled in the art. For example, the extracellular, transmembrane and cytoplasmic domains of the SARS-CoV-2 spike protein and the NDV F protein may be determined using publicly available information, GenBank, or websites such as, for example, the VIPR virus pathogen website (www.viprbrc.org), the DTU Bioinformatics domain website (www.cbs.dtu.dk / services / TMHMM / ), or programs available for determining transmembrane domains. See, for example, Table 2 below, in which the transmembrane and cytoplasmic domains of the NDV F protein are shown. In certain embodiments, the extracellular domain of the SARS-CoV-2 spike protein is fused to the transmembrane and cytoplasmic domains of the NDV F protein via a linker (e.g., GGGGS (SEQ ID NO: 7)).The linker can be any linker that does not interfere with the folding of the extracellular domain, the function of the extracellular domain, or both. In some embodiments, the linker is an amino acid sequence (e.g., a peptide) that is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 amino acids or more in length. In some embodiments, the linker is a glycine (G) linker or a glycine and serine (GS) linker. For example, the linker is (GGGGS). n where n is 1, 2, 3, 4, 5 or more (SEQ ID NO: 45). In another example, the linker may comprise a sequence of (G) n where n is 3, 4, 5, 6, 7, 8 or more. In certain embodiments, the linker comprises the sequence GGGGS (SEQ ID NO: 7). In some embodiments, the transmembrane and cytoplasmic domains of the NDV F protein are fused directly to the SARS-CoV-2 spike protein extracellular domain. In certain embodiments, the transgene encoding the chimeric F protein is codon optimized. See, e.g., Section 5.1.4 below for a discussion regarding codon optimization.

[0113] In another embodiment, described herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein, wherein the chimeric F protein comprises a derivative of the extracellular domain of the SARS-CoV-2 spike protein (e.g., a derivative of the extracellular domain of the SARS-CoV-2 spike protein described herein) and the transmembrane and cytoplasmic domains of the NDV F protein. In certain embodiments, the entire transmembrane and cytoplasmic domains of the NDV F protein are included in the chimeric F protein. In certain embodiments, the transmembrane and cytoplasmic domains of the NDV F protein comprise the amino acid sequence of SEQ ID NO: 42. In some embodiments, the NDV F protein is included in the chimeric F protein, rather than the entire transmembrane and cytoplasmic domains of the NDV F protein. In some embodiments, the entire transmembrane and cytoplasmic domains of the NDV F protein are not included in the chimeric F protein. For example, several amino acid residues (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 1-5, 1-10, or 5-15 amino acid residues) upstream of the transmembrane domain of the NDV F protein may be included in the chimeric F protein, and / or several amino acid residues (e.g., 1-5, 1-10, or 5-15 amino acid residues) downstream of the cytoplasmic domain of the NDV F protein may be included in the chimeric F protein. For example, several amino acid residues (e.g., 1, 2, 3, 4, 5, or 1-5 amino acid residues) smaller than the entire transmembrane domain of the NDV F protein may be included in the chimeric F protein, and / or several amino acid residues (e.g., 1, 2, 3, 4, 5, or 1-5 amino acid residues) smaller than the entire cytoplasmic domain of the NDV F protein may be included in the chimeric F protein.In another embodiment, described herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein, wherein the chimeric F protein comprises a derivative of the extracellular domain of the SARS-CoV-2 spike protein (e.g., a derivative of the extracellular domain of the SARS-CoV-2 spike protein described herein), a transmembrane domain of the NDV F protein + / - 1, 2, 3, 4, or 5 amino acid residues, and a cytoplasmic domain of the NDV F protein + / - 1, 2, 3, 4, or 5 amino acid residues. In certain embodiments, the chimeric F protein does not comprise the transmembrane and cytoplasmic domains of the SARS-CoV-2 spike protein. In some embodiments, 1, 2, or 3 amino acid residues of the transmembrane and / or cytoplasmic domains of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) are present in the chimeric F protein. In certain embodiments, a derivative of the extracellular domain of the SARS-CoV-2 spike protein lacks the polybasic cleavage site (e.g., one, two, or more residues corresponding to amino acid residues 682-685 (RRAR) of GenBank Accession No. MN908947.3 are replaced with other amino acid residues). In certain embodiments, a derivative has an amino acid residue corresponding to amino acid residues 682-685 (RRAR) of GenBank Accession No. MN908947.3 replaced with an alanine. See, for example, Table 2 below, in which the transmembrane and cytoplasmic domains of the NDV F protein are shown. In some embodiments, a derivative contains amino acid substitutions corresponding to the following amino acid residues of GenBank Accession No. MN908947.3: F817P, A892P, A899P, A942P, K986P, and V987P. In certain embodiments, the derivative contains amino acid residues corresponding to amino acid residues 682-685 (RRAR) of GenBank Accession No. MN908947.3 substituted with one alanine, and contains amino acid substitutions corresponding to the following amino acid residues of GenBank Accession No. MN908947.3: F817P, A892P, A899P, A942P, K986P, and V987P.In certain embodiments, a derivative of the extracellular domain of the SARS-CoV-2 spike protein is fused to the transmembrane and cytoplasmic domains of the NDV F protein via a linker (e.g., GGGGS (SEQ ID NO: 7)). The linker can be any linker that does not interfere with the folding of the extracellular domain, the function of the extracellular domain, or both. In some embodiments, the linker is an amino acid sequence (e.g., a peptide) that is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 amino acids or more in length. In some embodiments, the linker is a glycine (G) linker or a glycine and serine (GS) linker. For example, the linker is (GGGGS). n where n is 1, 2, 3, 4, 5 or more (SEQ ID NO: 45). In another example, the linker may comprise a sequence of (G) nwhere n is 3, 4, 5, 6, 7, 8 or more. In certain embodiments, the linker comprises the sequence GGGGS (SEQ ID NO: 7). In some embodiments, the transmembrane and cytoplasmic domains of the NDV F protein are directly fused to a derivative of the SARS-CoV-2 spike protein extracellular domain. In certain embodiments, described herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein, wherein the transgene comprises an RNA sequence corresponding to the negative sense of the cDNA sequence of SEQ ID NO: 5 or 43. In another specific embodiment, described herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein, wherein the chimeric F protein comprises an amino acid sequence of SEQ ID NO: 13 or 17, and the transmembrane and cytoplasmic domains of the NDV F protein. In certain embodiments, described herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein, wherein the transgene comprises an RNA sequence corresponding to the negative sense of the cDNA sequence of SEQ ID NO: 37 or 38. In another specific embodiment, described herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein, the chimeric F protein comprising the amino acid sequence of SEQ ID NO: 12 or 16, and the transmembrane and cytoplasmic domains of the NDV F protein. In a specific embodiment, described herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein, the transgene comprising an RNA sequence corresponding to the negative sense of the cDNA sequence of SEQ ID NO: 19 or 33. In another specific embodiment, described herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein, the chimeric F protein comprising the amino acid sequence of SEQ ID NO: 23 or 24, and the transmembrane and cytoplasmic domains of the NDV F protein. In a specific embodiment, described herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein, the transgene comprising an RNA sequence corresponding to the negative sense of the cDNA sequence of SEQ ID NO: 25 or 34.In another specific embodiment, described herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein, the chimeric F protein comprising the amino acid sequence of SEQ ID NO: 29 or 30, and the transmembrane and cytoplasmic domains of an NDV F protein. In a specific embodiment, the transgene encoding the chimeric F protein is codon optimized. For a discussion regarding codon optimization, see, e.g., Section 5.1.4 below. In a preferred embodiment, the transgene comprises a codon optimized version of a nucleic acid sequence encoding a chimeric F protein.

[0114] In certain embodiments, the transgene comprises a codon-optimized version of a nucleic acid sequence encoding a derivative of the extracellular domain of the SARS-CoV-2 spike protein. In certain embodiments, the transgene described herein comprises a nucleotide sequence encoding the amino acid sequence set forth in SEQ ID NO: 6 or 18. In another specific embodiment, the transgene described herein comprises a nucleotide sequence encoding the amino acid sequence set forth in SEQ ID NO: 11 or 40. In another specific embodiment, the transgene described herein comprises a nucleotide sequence encoding the amino acid sequence set forth in SEQ ID NO: 22 or 39. In another specific embodiment, the transgene described herein comprises a nucleotide sequence encoding the amino acid sequence set forth in SEQ ID NO: 28 or 41. In certain embodiments, the transgene described herein comprises a nucleotide sequence of SEQ ID NO: 5 or 43, or an RNA sequence corresponding to the negative sense of the cDNA sequence of SEQ ID NO: 5 or 43. In certain embodiments, the transgene described herein comprises a nucleotide sequence of SEQ ID NO: 37 or 38, or an RNA sequence corresponding to the negative sense of the cDNA sequence of SEQ ID NO: 37 or 38. In certain embodiments, the transgene described herein comprises a nucleotide sequence of SEQ ID NO: 19 or 33, or an RNA sequence corresponding to the negative sense of the cDNA sequence of SEQ ID NO: 19 or 33. In certain embodiments, the transgene described herein comprises a nucleotide sequence of SEQ ID NO: 25 or 34, or an RNA sequence corresponding to the negative sense of the cDNA sequence of SEQ ID NO: 25 or 34. In certain embodiments, the transgene encoding the chimeric F protein is integrated into the genome of any NDV type or strain (e.g., NDV Lasota strain). For types and strains of NDV that may be used, see, e.g., section 0 above. The transgene encoding the chimeric F protein may be integrated between any two NDV transcription units (e.g., between the P and M transcription units of NDV, between the NP and P transcription units of NDV, or between the HN and L transcription units of NDV, etc.).In certain embodiments, the NDV F protein transmembrane and cytoplasmic domains of the chimeric F protein are derived from the same NDV strain as the transcription unit of the NDV genome. In other embodiments, the NDV F protein transmembrane and cytoplasmic domains of the chimeric F protein are derived from a different NDV strain than the transcription unit of the NDV genome. In certain embodiments, the NDV genome is the genome of the LaSota strain.

[0115] In another embodiment, described herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein, wherein the chimeric F protein comprises an extracellular domain of a spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) + / - 1, 2, 3, 4, 5, 6, 7, 8 or more amino acid residues at the C-terminus of the extracellular domain, and a transmembrane domain and a cytoplasmic domain of an NDV F protein. In other words, the SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) spike protein portion of the chimeric F protein does not include the entire transmembrane domain and cytoplasmic domain of the SARS-CoV-2 spike protein. The extracellular domain, transmembrane domain, and cytoplasmic domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) and the NDV F protein may be determined using techniques known to those skilled in the art. For example, the extracellular, transmembrane and cytoplasmic domains of the SARS-CoV-2 spike protein and the NDV F protein may be determined using public information, GenBank, or websites such as the VIPR virus pathogen website (www.viprbrc.org), the DTU Bioinformatics domain website (www.cbs.dtu.dk / services / TMHMM / ), or programs available for determining transmembrane domains. See, for example, Table 2 below, in which the transmembrane and cytoplasmic domains of the NDV F protein are shown (SEQ ID NO: 42). In certain embodiments, the extracellular domain of the SARS-CoV-2 spike protein is fused to the transmembrane and cytoplasmic domains of the NDV F protein via a linker (e.g., GGGGS (SEQ ID NO: 7)). The linker may be any linker that does not interfere with the folding of the extracellular domain, the function of the extracellular domain, or both.In some embodiments, the linker is an amino acid sequence (e.g., a peptide) that is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 amino acids or more in length. In some embodiments, the linker is a glycine (G) linker or a glycine and serine (GS) linker. For example, the linker is (GGGGS). n where n is 1, 2, 3, 4, 5 or more (SEQ ID NO: 45). In another example, the linker may comprise a sequence of (G) n where n is 3, 4, 5, 6, 7, 8 or more. In certain embodiments, the linker comprises the sequence GGGGS (SEQ ID NO: 7). In some embodiments, the transmembrane and cytoplasmic domains of the NDV F protein are directly fused to the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant). In certain embodiments, the transgene encoding the chimeric F protein is codon optimized. See, e.g., Section 5.1.4 below for a discussion regarding codon optimization. In certain embodiments, the transgene encoding the chimeric F protein is integrated into the genome of any NDV type or strain (e.g., NDV Lasota strain). See, e.g., Section 0 above for types and strains of NDV that may be used. A transgene encoding a chimeric F protein may be integrated between any two NDV transcription units (e.g., between the P and M transcription units of NDV, between the NP and P transcription units of NDV, or between the HN and L transcription units of NDV). In certain embodiments, the NDV F protein transmembrane and cytoplasmic domains of the chimeric F protein are derived from the same NDV strain as the transcription unit of the NDV genome. In other embodiments, the NDV F protein transmembrane and cytoplasmic domains of the chimeric F protein are derived from a different NDV strain than the transcription unit of the NDV genome. In certain embodiments, the NDV genome is the genome of the LaSota strain.

[0116] In another embodiment, described herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein, wherein the chimeric F protein comprises a derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) and the transmembrane and cytoplasmic domains of the NDV F protein, wherein the derivative comprises + / - 1, 2, 3, 4, 5, 6, 7, 8 or more amino acid residues at the C-terminus of the extracellular domain. In other words, the SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) spike protein portion encoded by the chimeric F protein does not include the entire transmembrane and cytoplasmic domains of the SARS-CoV-2 spike protein. In certain embodiments, a derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) lacks a polybasic cleavage site (e.g., one, two, or more residues corresponding to amino acid residues 682-685 (RRAR) of GenBank Accession No. MN908947.3 are replaced with other amino acid residues). In certain embodiments, lacking a polybasic cleavage site means that the polybasic site is altered so that it is not cleaved, for example, by furin. In certain embodiments, the amino acid residues corresponding to amino acid residues 682-685 (RRAR) of GenBank Accession No. MN908947.3 are replaced with an alanine. In some embodiments, the derivative includes the following amino acid substitutions at amino acid residues corresponding to amino acid residues of GenBank Accession No. MN908947.3: F817P, A892P, A899P, A942P, K986P, and V987P.In certain embodiments, the derivative contains an alanine amino acid substitution at amino acid residues corresponding to amino acid residues 682-685 (RRAR) of GenBank Accession No. MN908947.3, and the following amino acid substitutions at amino acid residues corresponding to amino acid residues of GenBank Accession No. MN908947.3: F817P, A892P, A899P, A942P, K986P, and V987P. The extracellular, transmembrane, and cytoplasmic domains of the SARS-CoV-2 spike protein and the NDV F protein may be determined using techniques known to those of skill in the art. For example, the extracellular, transmembrane and cytoplasmic domains of the SARS-CoV-2 spike protein and the NDV F protein may be determined using public information, GenBank, or websites such as the VIPR virus pathogen website (www.viprbrc.org), the DTU Bioinformatics domain website (www.cbs.dtu.dk / services / TMHMM / ), or programs available for determining transmembrane domains. See, for example, Table 2 below, in which the transmembrane and cytoplasmic domains of the NDV F protein are shown. In certain embodiments, a derivative of the extracellular domain of the SARS-CoV-2 spike protein is fused to the transmembrane and cytoplasmic domains of the NDV F protein via a linker (e.g., GGGGS (SEQ ID NO: 7)). The linker may be any linker that does not interfere with the folding of the extracellular domain, the function of the extracellular domain, or both. In some embodiments, the linker is an amino acid sequence (e.g., a peptide) that is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 amino acids or more in length. In some embodiments, the linker is a glycine (G) linker or a glycine and serine (GS) linker. For example, the linker is (GGGGS). n where n is 1, 2, 3, 4, 5 or more (SEQ ID NO: 45). In another example, the linker may comprise a sequence of (G) nwhere n is 3, 4, 5, 6, 7, 8 or more. In certain embodiments, the linker comprises the sequence GGGGS (SEQ ID NO: 7). In some embodiments, the transmembrane and cytoplasmic domains of the NDV F protein are directly fused to a derivative of the SARS-CoV-2 spike protein extracellular domain. In certain embodiments, the transgene encoding the chimeric F protein is codon optimized. See, e.g., Section 5.1.4 below for a discussion of codon optimization. In certain embodiments, the transgene encoding the chimeric F protein is integrated into the genome of any NDV type or strain (e.g., NDV Lasota strain). See, e.g., Section 0 above for types and strains of NDV that may be used. The transgene encoding the chimeric F protein may be integrated between any two NDV transcription units (e.g., between the P and M transcription units of NDV, between the NP and P transcription units of NDV, or between the HN and L transcription units of NDV, etc.). In certain embodiments, the NDV F protein transmembrane and cytoplasmic domains of the chimeric F protein are derived from the same NDV strain as the transcription unit of the NDV genome. In other embodiments, the NDV F protein transmembrane and cytoplasmic domains of the chimeric F protein are derived from a different NDV strain than the transcription unit of the NDV genome. In certain embodiments, the NDV genome is the genome of the LaSota strain.

[0117] In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) in which one, two, three, four, five, six, seven, eight, nine, ten, eleven, twelve, thirteen, fourteen, fifteen, sixteen, seventeen, eighteen, nineteen, twenty, or more amino acids have been replaced with another amino acid (e.g., conservative amino acid substitutions), and the transmembrane and cytoplasmic domains of the NDV F protein. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), with 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids at the C-terminus of the extracellular domain replaced with another amino acid (e.g., conservative amino acid substitution), and the transmembrane and cytoplasmic domains of the NDV F protein. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), with 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids at the N-terminus of the extracellular domain replaced with another amino acid (e.g., conservative amino acid substitution), and the transmembrane and cytoplasmic domains of the NDV F protein.In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant), and the transmembrane and cytoplasmic domains of the NDV F protein, with 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids at the N-terminus being replaced with another amino acid (e.g., conservative amino acid substitution), and 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids at the C-terminus being replaced with another amino acid (e.g., conservative amino acid substitution). In some embodiments, the N-terminus is the N-terminal 100 amino acids of the extracellular domain. In some embodiments, the C-terminus is the C-terminal 100 amino acids of the extracellular domain. Examples of conservative amino acid substitutions include, for example, replacing an amino acid of one class with another amino acid of the same class. In certain embodiments, conservative substitutions do not change the structure or function, or both, of the polypeptide. Classes of amino acids include hydrophobic (Met, Ala, Val, Leu, Ile), neutral hydrophilic (Cys, Ser, Thr), acidic (Asp, Glu), basic (Asn, Gln, His, Lys, Arg), conformation disruptors (Gly, Pro), and aromatic (Trp, Tyr, Phe). In certain embodiments, the transgene encoding the chimeric F protein is integrated into the genome of any NDV type or strain (e.g., NDV Lasota strain). For types and strains of NDV that may be used, see, e.g., section 0 above. The transgene encoding the chimeric F protein may be integrated between any two NDV transcription units (e.g., between the P and M transcription units of NDV, between the NP and P transcription units of NDV, or between the HN and L transcription units of NDV, etc.). In a specific embodiment, the NDV F protein transmembrane and cytoplasmic domains of the chimeric F protein are derived from the same NDV strain as the transcription unit of the NDV genome.In certain embodiments, the transmembrane and cytoplasmic domains of the NDV F protein of the chimeric protein are derived from a different NDV strain than the transcription unit of the NDV genome. In certain embodiments, the NDV genome is the genome of the LaSota strain.

[0118] In another embodiment, provided herein is a transgene comprising a chimeric F protein, wherein the chimeric F protein comprises (or consists of) a derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) in which 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or 21 amino acids have been replaced with another amino acid (e.g., conservative amino acid substitutions), and the transmembrane and cytoplasmic domains of the NDV F protein. In certain embodiments, the derivative of the extracellular domain of the SARS-CoV-2 spike protein lacks a polybasic cleavage site (e.g., one, two, or more residues corresponding to amino acid residues 682-685 (RRAR) of GenBank Accession No. MN908947.3 have been replaced with another amino acid residue). In certain embodiments, lacking a polybasic cleavage site means that the polybasic site is altered so that it is not cleaved, for example, by furin. In certain embodiments, a derivative of the extracellular domain of the SARS-CoV-2 spike protein has an alanine substitution at amino acid residues corresponding to amino acid residues 682-685 (RRAR) of GenBank Accession No. MN908947.3. In some embodiments, the derivative contains the following amino acid substitutions at amino acid residues corresponding to amino acid residues of GenBank Accession No. MN908947.3: F817P, A892P, A899P, A942P, K986P, and V987P. In certain embodiments, the derivative contains a single alanine amino acid substitution at amino acid residues corresponding to amino acid residues 682-685 (RRAR) of GenBank Accession No. MN908947.3, and the following amino acid substitutions at amino acid residues corresponding to amino acid residues in GenBank Accession No. MN908947.3: F817P, A892P, A899P, A942P, K986P, and V987P.In certain embodiments, a derivative of the extracellular domain of the SARS-CoV-2 spike protein is fused to the transmembrane and cytoplasmic domains of the NDV F protein via a linker (e.g., GGGGS (SEQ ID NO: 7)). The linker can be any linker that does not interfere with the folding of the extracellular domain, the function of the extracellular domain, or both. In some embodiments, the linker is an amino acid sequence (e.g., a peptide) that is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 amino acids or more in length. In some embodiments, the linker is a glycine (G) linker or a glycine and serine (GS) linker. For example, the linker is (GGGGS). n where n is 1, 2, 3, 4, 5 or more (SEQ ID NO: 45). In another example, the linker may comprise a sequence of (G) nwhere n is 3, 4, 5, 6, 7, 8 or more. In certain embodiments, the linker comprises the sequence GGGGS (SEQ ID NO: 7). In some embodiments, a derivative of the extracellular domain of the SARS-CoV-2 spike protein is directly fused to the transmembrane and cytoplasmic domains of the NDV F protein. Examples of conservative amino acid substitutions include, for example, replacing an amino acid of one class with another amino acid of the same class. In certain embodiments, conservative substitutions do not change the structure or function of the polypeptide, or both. Classes of amino acids include hydrophobic (Met, Ala, Val, Leu, Ile), neutral hydrophilic (Cys, Ser, Thr), acidic (Asp, Glu), basic (Asn, Gln, His, Lys, Arg), conformational disruptors (Gly, Pro), and aromatic (Trp, Tyr, Phe). In certain embodiments, the transgene encoding the chimeric F protein is integrated into the genome of any NDV type or strain (e.g., NDV Lasota strain). For types and strains of NDV that may be used, see, e.g., section 0 above. The transgene encoding the chimeric F protein may be integrated between any two NDV transcription units (e.g., between the P and M transcription units of NDV, between the NP and P transcription units of NDV, or between the HN and L transcription units of NDV, etc.). In certain embodiments, the NDV F protein transmembrane and cytoplasmic domains of the chimeric F protein are derived from the same NDV strain as the transcription unit of the NDV genome. In certain embodiments, the NDV F protein transmembrane and cytoplasmic domains of the chimeric protein are derived from a different NDV strain than the transcription unit of the NDV genome. In certain embodiments, the NDV genome is the genome of the LaSota strain.

[0119] In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) with 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids deleted from the C-terminus, and the transmembrane and cytoplasmic domains of the NDV F protein. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) with 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids deleted from the C-terminus, and the transmembrane and cytoplasmic domains of the NDV F protein. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) the extracellular domain of a spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) with 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids deleted from the N-terminus, and the transmembrane and cytoplasmic domains of the NDV F protein. In some embodiments, the N-terminus of the extracellular domain is the N-terminal 100 amino acids. In some embodiments, the C-terminus of the extracellular domain is the C-terminal 100 amino acids. In certain embodiments, the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) is fused to the transmembrane and cytoplasmic domains of the NDV F protein via a linker (e.g., GGGGS (SEQ ID NO: 7)). The linker can be any linker that does not interfere with the folding of the extracellular domain, the function of the extracellular domain, or both.In some embodiments, the linker is an amino acid sequence (e.g., a peptide) that is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 amino acids or more in length. In some embodiments, the linker is a glycine (G) linker or a glycine and serine (GS) linker. For example, the linker is (GGGGS). n where n is 1, 2, 3, 4, 5 or more (SEQ ID NO: 45). In another example, the linker may comprise a sequence of (G) n where n is 3, 4, 5, 6, 7, 8 or more. In certain embodiments, the linker comprises the sequence GGGGS (SEQ ID NO: 7). In other embodiments, the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) is directly fused to the transmembrane and cytoplasmic domains of the NDV F protein. In certain embodiments, the transgene encoding the chimeric F protein is integrated into the genome of any NDV type or strain (e.g., NDV Lasota strain). For types and strains of NDV that may be used, see, e.g., section 0 above. The transgene encoding the chimeric F protein may be integrated between any two NDV transcription units (e.g., between the P and M transcription units of NDV, between the NP and P transcription units of NDV, or between the HN and L transcription units of NDV, etc.). In certain embodiments, the NDV F protein transmembrane and cytoplasmic domains of the chimeric F protein are derived from the same NDV strain as the transcription unit of the NDV genome. In other embodiments, the NDV F protein transmembrane and cytoplasmic domains of the chimeric F protein are derived from a different NDV strain than the transcription unit of the NDV genome. In certain embodiments, the NDV genome is the genome of the LaSota strain.

[0120] In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) a derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) in which 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids have been deleted from the C-terminus, and a chimeric F protein comprising (or consisting of) the transmembrane and cytoplasmic domains of the NDV F protein. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) a derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) in which 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids have been deleted from the C-terminus. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) in which 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acids have been deleted from the N-terminus, and a chimeric F protein comprising (or consisting of) the transmembrane and cytoplasmic domains of the NDV F protein. In certain embodiments, the derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) lacks a polybasic cleavage site (e.g., one, two, or more residues corresponding to amino acid residues 682-685 (RRAR) of GenBank Accession No. MN908947.3 are replaced with other amino acid residues). In certain embodiments, lacking a polybasic cleavage site means that the polybasic site is altered such that it cannot be cleaved by, for example, furin.In certain embodiments, the amino acid residues corresponding to amino acid residues 682-685 (RRAR) of GenBank Accession No. MN908947.3 are substituted with an alanine. In some embodiments, the derivative comprises the following amino acid substitutions at the amino acid residues corresponding to the amino acid residues of GenBank Accession No. MN908947.3: F817P, A892P, A899P, A942P, K986P, and V987P. In certain embodiments, the derivative comprises the amino acid substitution at the amino acid residues corresponding to amino acid residues 682-685 (RRAR) of GenBank Accession No. MN908947.3 with an alanine, and the following amino acid substitutions at the amino acid residues corresponding to the amino acid residues of GenBank Accession No. MN908947.3: F817P, A892P, A899P, A942P, K986P, and V987P. In certain embodiments, a derivative of the extracellular domain of the SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) spike protein is fused to the transmembrane and cytoplasmic domains of the NDV F protein via a linker (e.g., GGGGS (SEQ ID NO: 7)). The linker can be any linker that does not interfere with the folding of the extracellular domain, the function of the extracellular domain, or both. In some embodiments, the linker is an amino acid sequence (e.g., a peptide) that is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 amino acids or more in length. In some embodiments, the linker is a glycine (G) linker or a glycine and serine (GS) linker. For example, the linker is (GGGGS). n where n is 1, 2, 3, 4, 5 or more (SEQ ID NO: 45). In another example, the linker may comprise a sequence of (G) nwhere n is 3, 4, 5, 6, 7, 8 or more. In certain embodiments, the linker comprises the sequence GGGGS (SEQ ID NO: 7). In other embodiments, a derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) is directly fused to the transmembrane and cytoplasmic domains of the NDV F protein. In certain embodiments, a transgene encoding a chimeric F protein is integrated into the genome of any NDV type or strain (e.g., NDV Lasota strain). For types and strains of NDV that may be used, see, e.g., section 0 above. A transgene encoding a chimeric F protein may be integrated between any two NDV transcription units (e.g., between the P and M transcription units of NDV, between the NP and P transcription units of NDV, or between the HN and L transcription units of NDV, etc.). In certain embodiments, the NDV F protein transmembrane and cytoplasmic domains of the chimeric F protein are derived from the same NDV strain as the transcription unit of the NDV genome. In other embodiments, the NDV F protein transmembrane and cytoplasmic domains of the chimeric F protein are derived from a different NDV strain than the transcription unit of the NDV genome. In certain embodiments, the NDV genome is the genome of the LaSota strain.

[0121] In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) having one, two, three, four, five, six, seven, eight, nine, ten, eleven, twelve, thirteen, fourteen, fifteen, sixteen, seventeen, eighteen, nineteen, twenty, or more mutations (e.g., amino acid substitutions, amino acid deletions, amino acid additions, or a combination thereof) and the transmembrane and cytoplasmic domains of the NDV F protein. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) with 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acid substitutions and with 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acid deletions, and the transmembrane and cytoplasmic domains of the NDV F protein. In a particular embodiment, the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) is fused to the transmembrane and cytoplasmic domains of the NDV F protein via a linker (e.g., GGGGS (SEQ ID NO: 7)). The linker may be any linker that does not interfere with the folding of the extracellular domain, the function of the extracellular domain, or both. In some embodiments, the linker is an amino acid sequence (e.g., a peptide) that is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 amino acids or more in length. In some embodiments, the linker is a glycine (G) linker or a glycine and serine (GS) linker. For example, the linker is (GGGGS) n where n is 1, 2, 3, 4, 5 or more (SEQ ID NO: 45). In another example, the linker may comprise a sequence of (G) nwhere n is 3, 4, 5, 6, 7, 8 or more. In certain embodiments, the linker comprises the sequence GGGGS (SEQ ID NO: 7). In other embodiments, the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) is directly fused to the transmembrane and cytoplasmic domains of the NDV F protein. In certain embodiments, the transgene encoding the chimeric F protein is integrated into the genome of any NDV type or strain (e.g., NDV Lasota strain). For types and strains of NDV that may be used, see, e.g., section 0 above. The transgene encoding the chimeric F protein may be integrated between any two NDV transcription units (e.g., between the P and M transcription units of NDV, between the NP and P transcription units of NDV, or between the HN and L transcription units of NDV, etc.). In certain embodiments, the NDV F protein transmembrane and cytoplasmic domains of the chimeric F protein are derived from the same NDV strain as the transcription unit of the NDV genome. In other embodiments, the NDV F protein transmembrane and cytoplasmic domains of the chimeric F protein are derived from a different NDV strain than the transcription unit of the NDV genome. In certain embodiments, the NDV genome is the genome of the LaSota strain.

[0122] In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) having one, two, three, four, five, six, seven, eight, nine, ten, eleven, twelve, thirteen, fourteen, fifteen, sixteen, seventeen, eighteen, nineteen, twenty, or more mutations (e.g., amino acid substitutions, amino acid deletions, amino acid additions, or a combination thereof) and a chimeric F protein comprising (or consisting of) the transmembrane and cytoplasmic domains of the NDV F protein. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) having 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acid substitutions and having 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 amino acid deletions, and a chimeric F protein comprising (or consisting of) the transmembrane and cytoplasmic domains of the NDV F protein. In certain embodiments, the derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) lacks a polybasic cleavage site (e.g., one, two, or more residues corresponding to amino acid residues 682-685 (RRAR) of GenBank Accession No. MN908947.3 are substituted with other amino acid residues). In certain embodiments, lacking a polybasic cleavage site means that the polybasic site is altered such that it is not cleaved, for example, by furin. In certain embodiments, the amino acid residues corresponding to amino acid residues 682-685 (RRAR) of GenBank Accession No. MN908947.3 are substituted with an alanine. In some embodiments, the derivatives include the following amino acid substitutions at the amino acid residues corresponding to the amino acid residues of GenBank Accession No. MN908947.3: F817P, A892P, A899P, A942P, K986P, and V987P.In certain embodiments, the derivative comprises an alanine amino acid substitution at amino acid residues corresponding to amino acid residues 682-685 (RRAR) of GenBank Accession No. MN908947.3, and the following amino acid substitutions at amino acid residues corresponding to amino acid residues of GenBank Accession No. MN908947.3: F817P, A892P, A899P, A942P, K986P, and V987P. In certain embodiments, a derivative of the extracellular domain of the SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) spike protein is fused to the transmembrane and cytoplasmic domains of the NDV F protein via a linker (e.g., GGGGS (SEQ ID NO: 7)). The linker can be any linker that does not interfere with the folding of the extracellular domain, the function of the extracellular domain, or both. In some embodiments, the linker is an amino acid sequence (e.g., a peptide) that is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 amino acids or more in length. In some embodiments, the linker is a glycine (G) linker or a glycine and serine (GS) linker. For example, the linker is (GGGGS). n where n is 1, 2, 3, 4, 5 or more (SEQ ID NO: 45). In another example, the linker may comprise a sequence of (G) nwhere n is 3, 4, 5, 6, 7, 8 or more. In certain embodiments, the linker comprises the sequence GGGGS (SEQ ID NO: 7). In other embodiments, a derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) is directly fused to the transmembrane and cytoplasmic domains of the NDV F protein. In certain embodiments, a transgene encoding a chimeric F protein is integrated into the genome of any NDV type or strain (e.g., NDV Lasota strain). For types and strains of NDV that may be used, see, e.g., section 0 above. A transgene encoding a chimeric F protein may be integrated between any two NDV transcription units (e.g., between the P and M transcription units of NDV, between the NP and P transcription units of NDV, or between the HN and L transcription units of NDV, etc.). In certain embodiments, the NDV F protein transmembrane and cytoplasmic domains of the chimeric F protein are derived from the same NDV strain as the transcription unit of the NDV genome. In other embodiments, the NDV F protein transmembrane and cytoplasmic domains of the chimeric F protein are derived from a different NDV strain than the transcription unit of the NDV genome. In certain embodiments, the NDV genome is the genome of the LaSota strain.

[0123] In another embodiment, described herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein, wherein the chimeric F protein comprises a derivative of the extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) and the transmembrane and cytoplasmic domains of the NDV F protein, wherein the amino acid residues corresponding to amino acid residues 817, 892, 899, 942, 986, and 987 of the spike protein present in GenBank Accession No. MN908947.3 are replaced with proline, and wherein the derivative lacks a polybasic cleavage site. In certain embodiments, lacking a polybasic cleavage site means that the polybasic site is altered so that it is not cleaved, for example, by furin. The extracellular domain of the spike protein of SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) may lack a polybasic cleavage site as a result of a substitution of amino acid residues 682-685 of the polybasic cleavage site with an alanine. See, for example, Table 2 below, in which the transmembrane and cytoplasmic domains of the NDV F protein are shown. In certain embodiments, a derivative of the extracellular domain of the SARS-CoV-2 (e.g., Wuhan strain, delta variant, beta variant, or gamma variant) spike protein is fused to the transmembrane and cytoplasmic domains of the NDV F protein via a linker (e.g., GGGGS (SEQ ID NO: 7)). The linker may be any linker that does not interfere with the folding of the extracellular domain, the function of the extracellular domain, or both. In some embodiments, the linker is an amino acid sequence (e.g., a peptide) that is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 amino acids or more in length. In some embodiments, the linker is a glycine (G) linker or a glycine and serine (GS) linker. For example, the linker is (GGGGS) n where n is 1, 2, 3, 4, 5 or more (SEQ ID NO: 45). In another example, the linker may comprise a sequence of (G)n where n is 3, 4, 5, 6, 7, 8 or more. In certain embodiments, the linker comprises the sequence GGGGS (SEQ ID NO: 7). In some embodiments, the transmembrane and cytoplasmic domains of the NDV F protein are directly fused to a derivative of the SARS-CoV-2 spike protein extracellular domain. In certain embodiments, the transgene encoding the chimeric F protein is codon optimized. See, e.g., Section 5.1.4 below for a discussion of codon optimization. In certain embodiments, the transgene encoding the chimeric F protein is integrated into the genome of any NDV type or strain (e.g., NDV Lasota strain). See, e.g., Section 0 above for types and strains of NDV that may be used. The transgene encoding the chimeric F protein may be integrated between any two NDV transcription units (e.g., between the P and M transcription units of NDV, between the NP and P transcription units of NDV, or between the HN and L transcription units of NDV, etc.).

[0124] In another embodiment, provided herein is a transgene comprising a nucleotide sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to the nucleotide sequence of SEQ ID NO: 5. In another embodiment, provided herein is a transgene comprising a nucleotide sequence that is at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to the nucleotide sequence of SEQ ID NO: 5 or 43. In another embodiment, provided herein is a transgene comprising a nucleotide sequence that is at least 97%, at least 98%, or at least 99% identical to the nucleotide sequence of SEQ ID NO: 5 or 43. In another embodiment, provided herein is a transgene comprising a nucleotide sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to the nucleotide sequence of SEQ ID NO: 5 without the signal sequence. In another embodiment, provided herein is a transgene comprising a nucleotide sequence that is at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to the nucleotide sequence of SEQ ID NO:5 without the signal sequence. In another embodiment, provided herein is a transgene comprising a nucleotide sequence that is at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the nucleotide sequence of SEQ ID NO:5 without the signal sequence. In another embodiment, provided herein is a transgene comprising the nucleotide sequence of SEQ ID NO:5. In another embodiment, provided herein is a transgene comprising the nucleotide sequence of SEQ ID NO:43. In another embodiment, provided herein is a transgene comprising the nucleotide sequence of SEQ ID NO:5 without the signal sequence.In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) an amino acid sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 6 or 18. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) an amino acid sequence that is at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 6 or 18. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) an amino acid sequence that is at least 97%, at least 98%, or at least 99% identical to the amino acid sequence of SEQ ID NO: 6 or 18. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) an amino acid sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 6 without the signal sequence. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) an amino acid sequence that is 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: 6 without the signal sequence. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) an amino acid sequence that is at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 6 without the signal sequence.In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) the amino acid sequence of SEQ ID NO:6. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) the amino acid sequence of SEQ ID NO:18. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) the amino acid sequence of SEQ ID NO:6 without the signal sequence. Sequence identity may be determined using methods / techniques known in the art (see, for example, the "Best Fit" or "Gap" programs of the Sequence Analysis Software Package, version 10, Genetics Computer Group, Inc.). In certain embodiments, the transgene encoding the chimeric F protein is integrated into the genome of any NDV type or strain (e.g., NDV Lasota strain). For types and strains of NDV that may be used, see, for example, section 0 above. A transgene encoding a chimeric F protein may be integrated between any two NDV transcription units (e.g., between the P and M transcription units of NDV, between the NP and P transcription units of NDV, or between the HN and L transcription units of NDV). In certain embodiments, the NDV F protein transmembrane and cytoplasmic domains of the chimeric F protein are derived from the same NDV strain as the transcription unit of the NDV genome. In certain embodiments, the NDV F protein transmembrane and cytoplasmic domains of the chimeric F protein are derived from a different NDV strain than the transcription unit of the NDV genome. In certain embodiments, the NDV genome is the genome of the LaSota strain.

[0125] In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) an amino acid sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO:6, wherein the chimeric F protein comprises at least one, at least two, at least three, at least four, or more of the following amino acid modifications: T19R, G142D, delE156, R158G, L452R, T478K, and D950N. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) an amino acid sequence that is at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO:6. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) an amino acid sequence that is at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 18. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) an amino acid sequence that is at least 97%, at least 98%, or at least 99% identical to the amino acid sequence of SEQ ID NO: 6, wherein the chimeric F protein comprises at least one, at least two, at least three, at least four, or more of the following amino acid modifications: T19R, G142D, delE156, R158G, L452R, T478K, and D950N. In some embodiments, SEQ ID NO: 6 lacks a signal sequence. For signal sequences, see SEQ ID NO: 15.Methods / techniques known in the art may be used to determine sequence identity (see, e.g., the "Best Fit" or "Gap" programs of the Sequence Analysis Software Package, version 10, Genetics Computer Group, Inc.). In certain embodiments, the transgene encoding the chimeric F protein is integrated into the genome of any NDV type or strain (e.g., NDV Lasota strain). For types and strains of NDV that may be used, see, e.g., section 0 above. The transgene encoding the chimeric F protein may be integrated between any two NDV transcription units (e.g., between the P and M transcription units of NDV, between the NP and P transcription units of NDV, or between the HN and L transcription units of NDV, etc.). In certain embodiments, the NDV F protein transmembrane and cytoplasmic domains of the chimeric F protein are derived from the same NDV strain as the transcription unit of the NDV genome. In certain embodiments, the NDV F protein transmembrane and cytoplasmic domains of the chimeric F protein are derived from a different NDV strain than the transcription unit of the NDV genome. In a particular embodiment, the NDV genome is the genome of the LaSota strain.

[0126] In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein, wherein the chimeric F protein comprises (or consists of) an extracellular domain of a SARS-CoV-2 spike protein, and a transmembrane domain and a cytoplasmic domain of an NDV F protein, wherein the extracellular domain of the SARS-CoV-2 spike protein comprises an amino acid sequence that is at least 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to the amino acid sequence of SEQ ID NO: 13, or the amino acid sequence of SEQ ID NO: 13 without the signal sequence. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein, wherein the chimeric F protein comprises (or consists of) an extracellular domain of a SARS-CoV-2 spike protein and a transmembrane and cytoplasmic domain of an NDV F protein, wherein the extracellular domain of the SARS-CoV-2 spike protein comprises an amino acid sequence that is at least 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to the amino acid sequence of SEQ ID NO:17. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein, wherein the chimeric F protein comprises (or consists of) an extracellular domain of a SARS-CoV-2 spike protein, and a transmembrane domain and a cytoplasmic domain of an NDV F protein, wherein the extracellular domain of the SARS-CoV-2 spike protein comprises an amino acid sequence that is 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: 13, or the amino acid sequence of SEQ ID NO: 13 without the signal sequence.In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein, wherein the chimeric F protein comprises (or consists of) an extracellular domain of a SARS-CoV-2 spike protein and a transmembrane and cytoplasmic domain of an NDV F protein, wherein the extracellular domain of the SARS-CoV-2 spike protein comprises an amino acid sequence of SEQ ID NO: 13 or 17. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein, wherein the chimeric F protein comprises (or consists of) an amino acid sequence of SEQ ID NO: 6 or 18. In certain embodiments, the transgene encoding the chimeric F protein is codon optimized. For a discussion regarding codon optimization, see, e.g., Section 5.1.4 below. In certain embodiments, the transgene encoding the chimeric F protein is integrated into the genome of any NDV type or strain (e.g., NDV Lasota strain). For types and strains of NDV that may be used, see, e.g., Section 0 above. A transgene encoding a chimeric F protein may be integrated between any two NDV transcription units (e.g., between the P and M transcription units of NDV, between the NP and P transcription units of NDV, or between the HN and L transcription units of NDV). In certain embodiments, the NDV F protein transmembrane and cytoplasmic domains of the chimeric F protein are derived from the same NDV strain as the transcription unit of the NDV genome. In other embodiments, the NDV F protein transmembrane and cytoplasmic domains of the chimeric F protein are derived from a different NDV strain than the transcription unit of the NDV genome. In certain embodiments, the NDV genome is the genome of the LaSota strain.

[0127] In another embodiment, provided herein is a transgene comprising a nucleotide sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to the nucleotide sequence of SEQ ID NO: 19 or 33. In another embodiment, provided herein is a transgene comprising a nucleotide sequence that is at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to the nucleotide sequence of SEQ ID NO: 19 or 33. In another embodiment, provided herein is a transgene comprising a nucleotide sequence that is at least 97%, at least 98%, or at least 99% identical to the nucleotide sequence of SEQ ID NO: 19 or 33. In another embodiment, provided herein is a transgene comprising a nucleotide sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to the nucleotide sequence of SEQ ID NO: 19 without the signal sequence. In another embodiment, provided herein is a transgene comprising a nucleotide sequence that is at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to the nucleotide sequence of SEQ ID NO: 19 without the signal sequence. In another embodiment, provided herein is a transgene comprising a nucleotide sequence that is at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the nucleotide sequence of SEQ ID NO: 19 without the signal sequence. In another embodiment, provided herein is a transgene comprising the nucleotide sequence of SEQ ID NO: 19. In another embodiment, provided herein is a transgene comprising the nucleotide sequence of SEQ ID NO: 19 without the signal sequence. In another embodiment, provided herein is a transgene comprising the nucleotide sequence of SEQ ID NO: 33.In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) an amino acid sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 22 or 39. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) an amino acid sequence that is at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 22 or 39. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) an amino acid sequence that is at least 97%, at least 98%, or at least 99% identical to the amino acid sequence of SEQ ID NO: 22 or 39. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) an amino acid sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 22 without the signal sequence. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) an amino acid sequence that is 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: 22 without the signal sequence. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) an amino acid sequence that is at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 22 without the signal sequence.In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) the amino acid sequence of SEQ ID NO: 22. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) the amino acid sequence of SEQ ID NO: 39. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) the amino acid sequence of SEQ ID NO: 22 without the signal sequence. Sequence identity may be determined using methods / techniques known in the art (see, for example, the "Best Fit" or "Gap" programs of the Sequence Analysis Software Package, version 10, Genetics Computer Group, Inc.). In certain embodiments, the transgene encoding the chimeric F protein is integrated into the genome of any NDV type or strain (e.g., NDV Lasota strain). For types and strains of NDV that may be used, see, for example, section 0 above. A transgene encoding a chimeric F protein may be integrated between any two NDV transcription units (e.g., between the P and M transcription units of NDV, between the NP and P transcription units of NDV, or between the HN and L transcription units of NDV). In certain embodiments, the NDV F protein transmembrane and cytoplasmic domains of the chimeric F protein are derived from the same NDV strain as the transcription unit of the NDV genome. In certain embodiments, the NDV F protein transmembrane and cytoplasmic domains of the chimeric F protein are derived from a different NDV strain than the transcription unit of the NDV genome. In certain embodiments, the NDV genome is the genome of the LaSota strain.

[0128] In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein, wherein the chimeric F protein comprises (or consists of) an extracellular domain of a SARS-CoV-2 spike protein, and a transmembrane domain and a cytoplasmic domain of an NDV F protein, wherein the extracellular domain of the SARS-CoV-2 spike protein comprises an amino acid sequence that is at least 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to the amino acid sequence of SEQ ID NO:23, or the amino acid sequence of SEQ ID NO:23 without the signal sequence. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein, wherein the chimeric F protein comprises (or consists of) an extracellular domain of a SARS-CoV-2 spike protein and a transmembrane and cytoplasmic domain of an NDV F protein, wherein the extracellular domain of the SARS-CoV-2 spike protein comprises an amino acid sequence that is at least 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to the amino acid sequence of SEQ ID NO:24. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein, wherein the chimeric F protein comprises (or consists of) an extracellular domain of a SARS-CoV-2 spike protein and a transmembrane and cytoplasmic domain of an NDV F protein, wherein the extracellular domain of the SARS-CoV-2 spike protein comprises an amino acid sequence that is 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:23, or the amino acid sequence of SEQ ID NO:23 without the signal sequence.In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein, wherein the chimeric F protein comprises (or consists of) an extracellular domain of a SARS-CoV-2 spike protein and a transmembrane and cytoplasmic domain of an NDV F protein, wherein the extracellular domain of the SARS-CoV-2 spike protein comprises an amino acid sequence of SEQ ID NO: 23 or 24. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein, wherein the chimeric F protein comprises (or consists of) an amino acid sequence of SEQ ID NO: 22 or 39. In certain embodiments, the transgene encoding the chimeric F protein is codon optimized. For a discussion regarding codon optimization, see, e.g., Section 5.1.4 below. In certain embodiments, the transgene encoding the chimeric F protein is integrated into the genome of any NDV type or strain (e.g., NDV Lasota strain). For types and strains of NDV that may be used, see, e.g., Section 0 above. A transgene encoding a chimeric F protein may be integrated between any two NDV transcription units (e.g., between the P and M transcription units of NDV, between the NP and P transcription units of NDV, or between the HN and L transcription units of NDV). In certain embodiments, the NDV F protein transmembrane and cytoplasmic domains of the chimeric F protein are derived from the same NDV strain as the transcription unit of the NDV genome. In other embodiments, the NDV F protein transmembrane and cytoplasmic domains of the chimeric F protein are derived from a different NDV strain than the transcription unit of the NDV genome. In certain embodiments, the NDV genome is the genome of the LaSota strain.

[0129] In another embodiment, provided herein is a transgene comprising a nucleotide sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to the nucleotide sequence of SEQ ID NO: 37 or 38. In another embodiment, provided herein is a transgene comprising a nucleotide sequence that is at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to the nucleotide sequence of SEQ ID NO: 37 or 38. In another embodiment, provided herein is a transgene comprising a nucleotide sequence that is at least 97%, at least 98%, or at least 99% identical to the nucleotide sequence of SEQ ID NO: 37 or 38. In another embodiment, provided herein is a transgene comprising a nucleotide sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to the nucleotide sequence of SEQ ID NO: 37 without the signal sequence. In another embodiment, provided herein is a transgene comprising a nucleotide sequence that is at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to the nucleotide sequence of SEQ ID NO: 37 without the signal sequence. In another embodiment, provided herein is a transgene comprising a nucleotide sequence that is at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the nucleotide sequence of SEQ ID NO: 37 without the signal sequence. In another embodiment, provided herein is a transgene comprising the nucleotide sequence of SEQ ID NO: 37. In another embodiment, provided herein is a transgene comprising the nucleotide sequence of SEQ ID NO: 37 without the signal sequence. In another embodiment, provided herein is a transgene comprising the nucleotide sequence of SEQ ID NO: 38.In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) an amino acid sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 11 or 40. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) an amino acid sequence that is at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 11 or 40. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) an amino acid sequence that is at least 97%, at least 98%, or at least 99% identical to the amino acid sequence of SEQ ID NO: 11 or 40. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) an amino acid sequence that is at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 11 without the signal sequence. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a protein comprising (or consisting of) an amino acid sequence that is 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: 11 without the signal sequence. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) an amino acid sequence that is at least 97%, at least 98%, at least 99%, or at least 99.5% identical to the amino acid sequence of SEQ ID NO: 11 without the signal sequence.In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) the amino acid sequence of SEQ ID NO: 11. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) the amino acid sequence of SEQ ID NO: 40. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein comprising (or consisting of) the amino acid sequence of SEQ ID NO: 11 without the signal sequence. Sequence identity may be determined using methods / techniques known in the art (see, for example, the "Best Fit" or "Gap" programs of the Sequence Analysis Software Package, version 10, Genetics Computer Group, Inc.). In certain embodiments, the transgene encoding the chimeric F protein is integrated into the genome of any NDV type or strain (e.g., NDV Lasota strain). For types and strains of NDV that may be used, see, for example, section 0 above. A transgene encoding a chimeric F protein may be integrated between any two NDV transcription units (e.g., between the P and M transcription units of NDV, between the NP and P transcription units of NDV, or between the HN and L transcription units of NDV). In certain embodiments, the NDV F protein transmembrane and cytoplasmic domains of the chimeric F protein are derived from the same NDV strain as the transcription unit of the NDV genome. In certain embodiments, the NDV F protein transmembrane and cytoplasmic domains of the chimeric F protein are derived from a different NDV strain than the transcription unit of the NDV genome. In certain embodiments, the NDV genome is the genome of the LaSota strain.

[0130] In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein, wherein the chimeric F protein comprises (or consists of) an extracellular domain of a SARS-CoV-2 spike protein, and a transmembrane domain and a cytoplasmic domain of an NDV F protein, wherein the extracellular domain of the SARS-CoV-2 spike protein comprises an amino acid sequence that is at least 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to the amino acid sequence of SEQ ID NO: 12, or the amino acid sequence of SEQ ID NO: 12 without the signal sequence. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein, wherein the chimeric F protein comprises (or consists of) an extracellular domain of a SARS-CoV-2 spike protein and a transmembrane and cytoplasmic domain of an NDV F protein, wherein the extracellular domain of the SARS-CoV-2 spike protein comprises an amino acid sequence that is at least 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to the amino acid sequence of SEQ ID NO: 16. In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein, wherein the chimeric F protein comprises (or consists of) an extracellular domain of a SARS-CoV-2 spike protein, and a transmembrane domain and a cytoplasmic domain of an NDV F protein, wherein the extracellular domain of the SARS-CoV-2 spike protein comprises an amino acid sequence that is 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: 12, or the amino acid sequence of SEQ ID NO: 12 without the signal sequence.In another embodiment, provided herein is a transgene comprising a nucleotide sequence encoding a chimeric F protein, wherein the chimeric F protein comprises (or consists of) an extracellular domain of a SARS-CoV-2 spike protein and a transmembrane and cytoplasmic domain of an NDV F protein, wherein the extracellular domain of the SARS-CoV-2 spike protein comprises an amino acid sequ...

Claims

1. An immunogenic composition, (a) a first recombinant NDV comprising a first transgene comprising a nucleotide sequence encoding a first chimeric protein, including (i) a first derivative of the extracellular domain of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein, and (ii) a first transgene comprising a nucleotide sequence encoding a first chimeric protein, including the transmembrane domain and cytoplasmic domain of the fusion (F) protein of Newcastle disease virus (NDV), and (b) A second recombinant NDV comprising (i) a second derivative of the extracellular domain of the SARS-CoV-2 spike protein, and (ii) a second transgene comprising a nucleotide sequence encoding a second chimeric protein, including the transmembrane domain and cytoplasmic domain of the NDV F protein, Includes, The first derivative of the extracellular domain of the SARS-CoV-2 spike protein and the second derivative of the extracellular domain of the SARS-CoV-2 spike protein are immunogenic compositions derived from different variants.

2. (A) The first derivative of the extracellular domain of the SARS-CoV-2 spike protein and the second derivative of the extracellular domain of the SARS-CoV-2 spike protein each include an amino acid substitution to proline at positions corresponding to the 817th, 892nd, 899th, 942nd, 986th, and 987th positions of the Wuhan strain spike protein, and a substitution from RRAR to alanine at positions corresponding to the 682nd to 685th positions of the Wuhan strain spike protein, (B) (i) The first derivative of the extracellular domain of the SARS-CoV-2 spike protein contains at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 12 or 16, and the second derivative of the extracellular domain of the SARS-CoV-2 spike protein contains at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 13, 17, 23, 24, 29 or 30, or a combination thereof. (ii) The first derivative of the extracellular domain of the SARS-CoV-2 spike protein contains at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 23 or 24, and the second derivative of the extracellular domain of the SARS-CoV-2 spike protein contains at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 13, 17, 29 or 30, or a combination thereof, (iii) The first derivative of the extracellular domain of the SARS-CoV-2 spike protein contains at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 29 or 30, and the second derivative of the extracellular domain of the SARS-CoV-2 spike protein contains at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 13 or 17, or a combination thereof. It is one of them, or (C) combinations of those, The immunogenic composition according to claim 1.

3. A polyvalent immunogenic composition, (a) First recombinant NDV, and (b) The second recombinable NDV according to claim 1, and (c) A third recombinant NDV comprising (i) a third derivative of the extracellular domain of the SARS-CoV-2 spike protein, and (ii) a third transgene comprising a nucleotide sequence encoding a third chimeric protein, including the transmembrane domain and cytoplasmic domain of the NDV F protein, Includes, A polyvalent immunogenic composition in which a first derivative of the extracellular domain of the SARS-CoV-2 spike protein, a second derivative of the extracellular domain of the SARS-CoV-2 spike protein, and a third derivative of the extracellular domain of the SARS-CoV-2 spike protein are distinct from each other.

4. (A) Each of the first derivative of the extracellular domain of the SARS-CoV-2 spike protein, the second derivative of the extracellular domain of the SARS-CoV-2 spike protein, and the third derivative of the extracellular domain of the SARS-CoV-2 spike protein comprises an amino acid substitution to proline at positions corresponding to the 817th, 892nd, 899th, 942nd, 986th, and 987th positions of the Wuhan strain spike protein, and comprises a substitution from RRAR to alanine at positions corresponding to the 682nd to 685th positions of the Wuhan strain spike protein, (B) (i) The first derivative of the extracellular domain of the SARS-CoV-2 spike protein contains at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 12 or 16, the second derivative of the extracellular domain of the SARS-CoV-2 spike protein contains at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 13 or 17, and the third derivative of the extracellular domain of the SARS-CoV-2 spike protein contains at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 29 or 30, or a combination thereof. (ii) The first derivative of the extracellular domain of the SARS-CoV-2 spike protein contains at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 23 or 24; the second derivative of the extracellular domain of the SARS-CoV-2 spike protein contains at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 12, 13, 16 or 17; and the third derivative of the extracellular domain of the SARS-CoV-2 spike protein contains at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 29 or 30, or a combination thereof. (iii) The first derivative of the extracellular domain of the SARS-CoV-2 spike protein contains at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 29 or 30, and the second derivative of the extracellular domain of the SARS-CoV-2 spike protein contains at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 12, 13, 16 or 17, or a combination thereof, (iv) The first derivative of the extracellular domain of the SARS-CoV-2 spike protein contains at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 13 or 17, the second derivative of the extracellular domain of the SARS-CoV-2 spike protein contains at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 23 or 24, the third derivative of the extracellular domain of the SARS-CoV-2 spike protein contains at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 23 or 24, or a combination thereof. It is one of them, or (C) combinations of those, The polyvalent immunogenic composition according to claim 3.

5. The polyvalent immunogenic composition according to claim 3, further comprising a fourth recombinant NDV, the fourth recombinant NDV comprising a fourth transgene comprising a nucleotide sequence encoding a fourth chimeric protein comprising (i) a fourth derivative of the extracellular domain of the SARS-CoV-2 spike protein, and (ii) a fourth transgene comprising a nucleotide sequence encoding a fourth chimeric protein comprising the transmembrane domain and cytoplasmic domain of the F protein of the NDV, wherein the fourth derivative of the extracellular domain of the SARS-CoV-2 spike protein is different from the first derivative of the extracellular domain of the SARS-CoV-2 spike protein, the second derivative of the extracellular domain of the SARS-CoV-2 spike protein, and the third derivative of the extracellular domain of the SARS-CoV-2 spike protein.

6. Each of the first derivative of the extracellular domain of the SARS-CoV-2 spike protein, the second derivative of the extracellular domain of the SARS-CoV-2 spike protein, and the third derivative of the extracellular domain of the SARS-CoV-2 spike protein comprises an amino acid substitution to proline at positions corresponding to 817, 892, 899, 942, 986, and 987 of the Wuhan strain spike protein, and comprises a substitution from RRAR to alanine at positions corresponding to 682 to 685 of the Wuhan strain spike protein, The fourth derivative of the extracellular domain of the SARS-CoV-2 spike protein includes an amino acid substitution to proline at positions corresponding to positions 817, 892, 899, 942, 986, and 987 of the Wuhan strain spike protein, and includes a substitution from RRAR to alanine at positions corresponding to positions 682 to 685 of the Wuhan strain spike protein, or The combination of those, The polyvalent immunogenic composition according to claim 5.

7. The first derivative of the extracellular domain of the SARS-CoV-2 spike protein, the second derivative of the extracellular domain of the SARS-CoV-2 spike protein, and the third derivative of the extracellular domain of the SARS-CoV-2 spike protein are as defined in (B)(i), The polyvalent immunogenic composition further comprises a fourth recombinant NDV, the fourth recombinant NDV comprising (i) a fourth derivative of the extracellular domain of the SARS-CoV-2 spike protein having at least 90% identical amino acid sequence to the amino acid sequence of SEQ ID NO: 23 or 24, and (ii) a fourth transgene comprising a nucleotide sequence encoding a fourth chimeric protein comprising the transmembrane domain and cytoplasmic domain of the NDV F protein. The polyvalent immunogenic composition according to claim 4.

8. An immunogenic composition, (a) (i) a first derivative of the extracellular domain of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein, and (ii) a first recombinant NDV comprising a first chimeric protein comprising the transmembrane domain and cytoplasmic domain of the fusion (F) protein of Newcastle disease virus (NDV), and (b) (i) a second derivative of the extracellular domain of the SARS-CoV-2 spike protein, and (ii) a second recombinant NDV comprising a second chimeric protein including the transmembrane domain and cytoplasmic domain of the NDV F protein, Includes, The first derivative of the extracellular domain of the SARS-CoV-2 spike protein and the second derivative of the extracellular domain of the SARS-CoV-2 spike protein are immunogenic compositions derived from different variants.

9. (A) The first derivative of the extracellular domain of the SARS-CoV-2 spike protein and the second derivative of the extracellular domain of the SARS-CoV-2 spike protein each include an amino acid substitution to proline at positions corresponding to the 817th, 892nd, 899th, 942nd, 986th, and 987th positions of the Wuhan strain spike protein, and a substitution from RRAR to alanine at positions corresponding to the 682nd to 685th positions of the Wuhan strain spike protein, (B) (i) The first derivative of the extracellular domain of the SARS-CoV-2 spike protein contains at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 12 or 16, and the second derivative of the extracellular domain of the SARS-CoV-2 spike protein contains at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 13, 17, 23, 24, 29 or 30, or a combination thereof. (ii) The first derivative of the extracellular domain of the SARS-CoV-2 spike protein contains at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 23 or 24, and the second derivative of the extracellular domain of the SARS-CoV-2 spike protein contains at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 13, 17, 29 or 30, or a combination thereof. (iii) The first derivative of the extracellular domain of the SARS-CoV-2 spike protein contains at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 29 or 30, and the second derivative of the extracellular domain of the SARS-CoV-2 spike protein contains at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 13 or 17, or a combination thereof. It is one of them, or (C) combinations of those, The immunogenic composition according to claim 8.

10. A polyvalent immunogenic composition, (a) First recombinant NDV, and (b) The second recombinable NDV according to claim 8, and (c) (i) a third derivative of the extracellular domain of the SARS-CoV-2 spike protein, and (ii) a third recombinant NDV comprising a third chimeric protein including the transmembrane domain and cytoplasmic domain of the F protein of NDV, Includes, The first derivative of the extracellular domain of the SARS-CoV-2 spike protein, the second derivative of the extracellular domain of the SARS-CoV-2 spike protein, and the third derivative of the extracellular domain of the SARS-CoV-2 spike protein are polyvalent immunogenic compositions derived from different variants.

11. (A) Each of the first derivative of the extracellular domain of the SARS-CoV-2 spike protein, the second derivative of the extracellular domain of the SARS-CoV-2 spike protein, and the third derivative of the extracellular domain of the SARS-CoV-2 spike protein comprises an amino acid substitution to proline at positions corresponding to the 817th, 892nd, 899th, 942nd, 986th, and 987th positions of the Wuhan strain spike protein, and comprises a substitution from RRAR to alanine at positions corresponding to the 682nd to 685th positions of the Wuhan strain spike protein, (B) (i) The first derivative of the extracellular domain of the SARS-CoV-2 spike protein contains at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 12 or 16, the second derivative of the extracellular domain of the SARS-CoV-2 spike protein contains at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 13 or 17, and the third derivative of the extracellular domain of the SARS-CoV-2 spike protein contains at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 29 or 30, or a combination thereof. (ii) The first derivative of the extracellular domain of the SARS-CoV-2 spike protein contains at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 23 or 24; the second derivative of the extracellular domain of the SARS-CoV-2 spike protein contains at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 12, 13, 16 or 17; and the third derivative of the extracellular domain of the SARS-CoV-2 spike protein contains at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 29 or 30, or a combination thereof. (iii) The first derivative of the extracellular domain of the SARS-CoV-2 spike protein contains at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 29 or 30, and the second derivative of the extracellular domain of the SARS-CoV-2 spike protein contains at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 13 or 17, or a combination thereof. It is one of them, or (C) combinations of those, The polyvalent immunogenic composition according to claim 10.

12. Each of the first derivative of the extracellular domain of the SARS-CoV-2 spike protein, the second derivative of the extracellular domain of the SARS-CoV-2 spike protein, and the third derivative of the extracellular domain of the SARS-CoV-2 spike protein comprises an amino acid substitution to proline at positions corresponding to 817, 892, 899, 942, 986, and 987 of the Wuhan strain spike protein, and comprises a substitution from RRAR to alanine at positions corresponding to 682 to 685 of the Wuhan strain spike protein, The polyvalent immunogenic composition further comprises (i) a fourth derivative of the extracellular domain of the SARS-CoV-2 spike protein, and (ii) a fourth recombinant NDV comprising a fourth chimeric protein including the transmembrane domain and cytoplasmic domain of the F protein of the NDV, wherein the fourth derivative of the extracellular domain of the SARS-CoV-2 spike protein is derived from something different from the first derivative, the second derivative, and the third derivative, or The combination of those, The polyvalent immunogenic composition according to claim 10.

13. The first derivative of the extracellular domain of the SARS-CoV-2 spike protein, the second derivative of the extracellular domain of the SARS-CoV-2 spike protein, and the third derivative of the extracellular domain of the SARS-CoV-2 spike protein are as defined in (B)(i), The polyvalent immunogenic composition further comprises (i) a fourth derivative of the extracellular domain of the SARS-CoV-2 spike protein having an amino acid sequence at least 90% identical to the amino acid sequence of SEQ ID NO: 23 or 24, and (ii) a fourth recombinant NDV comprising a fourth chimeric protein having a transmembrane domain and a cytoplasmic domain of the NDV F protein. The polyvalent immunogenic composition according to claim 11.

14. The extracellular domain of the chimeric protein is linked to the transmembrane domain and cytoplasmic domain of the F protein of the NDV via a linker, or a linker containing the amino acid sequence of SEQ ID NO:

7. The transmembrane domain and cytoplasmic domain of the F protein of the aforementioned NDV include the amino acid sequence of SEQ ID NO:

42. The recombinant NDV is either inactivated or alive. The immunogenic composition further comprises an adjuvant, or The combination of those, The immunogenic composition according to any one of claims 1, 3, 8, and 10.

15. An immunogenic composition, (a) A first recombinant Newcastle disease virus (NDV) comprising a first transgene comprising a first transgene comprising a nucleotide sequence encoding a first chimeric protein having at least 90% identical amino acid sequence to the amino acid sequence of SEQ ID NO: 11 or 40, and a second recombinant NDV comprising a second transgene comprising a second transgene comprising a nucleotide sequence encoding a second chimeric protein having at least 90% identical amino acid sequence to the amino acid sequence of SEQ ID NO: 6, 18, 22, 28, 39 or 41, (b) A first recombinant NDV comprising a first transgene comprising a nucleotide sequence encoding a first chimeric protein, which comprises at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 28 or 41, and a second recombinant NDV comprising a second transgene comprising a nucleotide sequence encoding a second chimeric protein, which comprises at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 22 or 39, (c) A first recombinant NDV comprising a first transgene comprising a nucleotide sequence encoding a first chimeric protein, which comprises at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 28 or 41, and a second recombinant NDV comprising a second transgene comprising a nucleotide sequence encoding a second chimeric protein, which comprises at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 6 or 18. (d) A first recombinant NDV comprising a first transgene comprising a nucleotide sequence encoding a first chimeric protein, which comprises at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 6 or 18, and a second recombinant NDV comprising a second transgene comprising a nucleotide sequence encoding a second chimeric protein, which comprises at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 22 or 39. (e) A first recombinant NDV comprising a first transgene comprising a nucleotide sequence encoding a first chimeric protein, which comprises at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 11 or 40; a second recombinant NDV comprising a second transgene comprising a nucleotide sequence encoding a second chimeric protein, which comprises at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 22 or 39; and a third recombinant NDV comprising a third transgene comprising a nucleotide sequence encoding a third chimeric protein, which comprises at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 6, 18, 28 or 41. (f) A first recombinant NDV comprising a first transgene comprising a nucleotide sequence encoding a first chimeric protein, which comprises at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 28 or 41; a second recombinant NDV comprising a second transgene comprising a nucleotide sequence encoding a second chimeric protein, which comprises at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 22 or 39; and a third recombinant NDV comprising a third transgene comprising a nucleotide sequence encoding a third chimeric protein, which comprises at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 6 or 18. (g) A first recombinant NDV comprising a first transgene comprising a nucleotide sequence encoding a first chimeric protein, which comprises at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 11 or 40; a second recombinant NDV comprising a second transgene comprising a nucleotide sequence encoding a second chimeric protein, which comprises at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 22 or 39; a third recombinant NDV comprising a third transgene comprising a nucleotide sequence encoding a third chimeric protein, which comprises at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 6 or 18; and a fourth recombinant NDV comprising a fourth transgene comprising a nucleotide sequence encoding a fourth chimeric protein, which comprises at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 28 or 41. (h) A first recombinant NDV comprising a first chimeric protein having at least 90% identical amino acid sequence to the amino acid sequence of SEQ ID NO: 11 or 40, and a second recombinant NDV comprising a second chimeric protein having at least 90% identical amino acid sequence to the amino acid sequence of SEQ ID NO: 6, 18, 22, 28, 39 or 41, (i) A first recombinant NDV comprising a first chimeric protein having at least 90% identical amino acid sequence to the amino acid sequence of SEQ ID NO: 28 or 41, and a second recombinant NDV comprising a second chimeric protein having at least 90% identical amino acid sequence to the amino acid sequence of SEQ ID NO: 6 or 18, (j) A first recombinant NDV comprising a first chimeric protein having at least 90% identical amino acid sequence to the amino acid sequence of SEQ ID NO: 28 or 41, and a second recombinant NDV comprising a second chimeric protein having at least 90% identical amino acid sequence to the amino acid sequence of SEQ ID NO: 22 or 39, (k) A first recombinant NDV comprising a first chimeric protein having at least 90% identical amino acid sequence to the amino acid sequence of SEQ ID NO: 6 or 18, and a second recombinant NDV comprising a second chimeric protein having at least 90% identical amino acid sequence to the amino acid sequence of SEQ ID NO: 22 or 39, (l) A first recombinant NDV comprising a first chimeric protein having at least 90% identical amino acid sequence to the amino acid sequence of SEQ ID NO: 11 or 40, a second recombinant NDV comprising a second chimeric protein having at least 90% identical amino acid sequence to the amino acid sequence of SEQ ID NO: 22 or 39, and a third recombinant NDV comprising a third chimeric protein having at least 90% identical amino acid sequence to the amino acid sequence of SEQ ID NO: 6, 18, 28 or 41. (m) A first recombinant NDV comprising a first chimeric protein containing at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 28 or 41; a second recombinant NDV comprising a second chimeric protein containing at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 22 or 39; and a third recombinant NDV comprising a third chimeric protein containing at least 90% identical amino acid sequences to the amino acid sequence of SEQ ID NO: 6 or 18, or (n) A first recombinant NDV comprising a first chimeric protein having at least 90% identical amino acid sequence to the amino acid sequence of SEQ ID NO: 11 or 40; a second recombinant NDV comprising a second chimeric protein having at least 90% identical amino acid sequence to the amino acid sequence of SEQ ID NO: 22 or 39; a third recombinant NDV comprising a third chimeric protein having at least 90% identical amino acid sequence to the amino acid sequence of SEQ ID NO: 6 or 18; and a fourth recombinant NDV comprising a fourth chimeric protein having at least 90% identical amino acid sequence to the amino acid sequence of SEQ ID NO: 28 or 41. A polyvalent immunogenic composition containing the above.

16. The recombinant NDV is either inactivated or alive. The immunogenic composition further comprises an adjuvant, or That combination is, The immunogenic composition according to any one of claims 1, 3, 8, 10, and 15.

17. An immunogenic composition according to any one of claims 1, 3, 8, 10, and 15 for inducing an immune response to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein in a subject.

18. An immunogenic composition according to any one of claims 1, 3, 8, 10, and 15 for preventing coronavirus disease 2019 (COVID-19) in a subject.

19. An immunogenic composition according to any one of claims 1, 3, 8, 10, and 15 for conferring immunity to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) to a subject.

20. An immunogenic composition according to any one of claims 1, 3, 8, 10, and 15, for conferring immunity to two or more severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in a subject.

21. An immunogenic composition according to any one of claims 1, 3, 8, 10, and 15, wherein one or more severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is different from the SARS-CoV-2 from which the extracellular domain of the chimeric protein contained in the immunogenic composition originates, for conferring immunity to one or more SARS-CoV-2 to a subject.

22. An immunogenic composition according to any one of claims 1, 3, 8, 10, and 15, wherein one or more severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is different from the SARS-CoV-2 from which the extracellular domain of the chimeric protein contained in the immunogenic composition originates, for inducing antibodies that neutralize one or more SARS-CoV-2 in a subject.

23. An immunogenic composition according to any one of claims 1, 3, 8, 10, and 15, wherein the spike proteins of one or more severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are heterogeneous from the SARS-CoV-2 spike proteins derived from the extracellular domain contained in the immunogenic composition, for inducing antibodies that cross-react with one or more SARS-CoV-2 spike proteins in a subject.

24. The composition is administered intranasally or intramuscularly to the subject. The subject is a human, The aforementioned individuals have previously received the COVID-19 vaccine. The subject is administered at least once with a booster of the pharmaceutical composition, or That combination is, The immunogenic composition according to claim 17.

25. A kit comprising the immunogenic composition according to any one of claims 1, 3, 8, 10, and 15.

Images