Chimeric fusion proteins as respiratory syncytial virus (RSV) vaccines

Abstract

The present invention provides chimeric polypeptides comprising a respiratory syncytial virus (RSV) fusion protein (F) and a structure-stabilizing moiety (SSM). Further provided are nucleic acids and nucleic acid vectors encoding such chimeric polypeptides as well as compositions and kits comprising such chimeric polypeptides or such nucleic acids. The present invention further provides methods and uses employing the herein provided chimeric polypeptides, the herein provided nucleic acids, the herein provided compositions, or the herein provided kits in the immunization and / or vaccination of a subject. Further provided are methods of production of antigen-binding molecules that bind to the herein provided chimeric polypeptides as well as the corresponding antigen-binding molecules.

Description

[0001] New PCT patent application The University of Queensland Vossius Ref.: AJ2843 PCT BS Chimeric fusion proteins as respiratory syncytial virus (RSV) vaccines This application claims the benefit of priority of European patent application EP24193720.0 filed on August 08, 2024 and of European patent application EP25183882.7 filed on June 18, 2025, each of which is incorporated herein by reference in its entirety. The present invention provides chimeric polypeptides comprising a respiratory syncytial virus (RSV) fusion protein (F) and a structure-stabilizing moiety (SSM). Further provided are nucleic acids and nucleic acid vectors encoding such chimeric polypeptides as well as compositions and kits comprising such chimeric polypeptides or such nucleic acids. The present invention further provides methods and uses employing the herein provided chimeric polypeptides, the herein provided nucleic acids, the herein provided compositions, or the herein provided kits in the immunization and / or vaccination of a subject. Further provided are methods of production of antigen-binding molecules that bind to the herein provided chimeric polypeptides as well as the corresponding antigen-binding molecules. Respiratory syncytial virus (RSV) is a prevalent respiratory virus that poses a significant health burden, particularly amongst infants, young children, the elderly, and individuals with underlying medical conditions. There have been various attempts to develop vaccines for the prevention of RSV infections, including approaches relying on the RSV fusion protein as antigen. Notably, stabilization of the RSV fusion protein in the pre-fusion conformation is necessary to allow effective immunization against RSV. As of 2024, three RSV vaccines have been approved by the U.S. Food and Drug Administration (FDA). Two of these comprise lyophilized pre-fusion-stabilized RSV fusion protein that needs to be reconstituted prior to administration (Arexvy®, GSK and Abrysvo®, Pfizer). A third comprises lipid nanoparticle (LNP) encapsulated mRNA encoding pre-fusion-stabilized RSV fusion protein that also needs to be stored frozen (mRESVIA®, Moderna). While the above-mentioned approved RSV vaccines have demonstrated protective efficacy, the requirement for reconstitution and frozen storage is suboptimal for both distribution and administration. Further improvements in pre-fusion stabilization would be necessary to achieve an easy- to-administer liquid formulation. There is hence still an unmet need for novel and improved vaccines against RSV, particularly vaccines exhibiting improved stabilization of the pre-fusion conformation of the RSV fusion protein, improved storage stability, improved vaccine immunogenicity and / or improved vaccine efficacy. The present invention addresses the above-discussed shortcomings affecting RSV vaccines available in the state of the art and solves the technical problem of providing novel and improved means and methods for the immunization and / or vaccination of a subject against respiratory syncytial virus. Accordingly, in a first aspect, the present invention provides a chimeric polypeptide comprising a respiratory syncytial virus (RSV) fusion protein and a structure-stabilizing moiety, wherein said RSV fusion protein comprises an amino acid sequence having at least about 90% sequence identity to the amino acid sequence set forth in SEQ ID NO: 26, wherein said RSV fusion protein comprises a C-terminal amino acid sequence consisting of the amino acid sequence IRK or IRR (preferably IRK), wherein said structure-stabilizing moiety comprises a first heptad repeat region (FHRR) and a second heptad repeat region (SHRR), wherein said FHRR comprises an amino acid sequence having at least about 90% sequence identity to the amino acid sequence set forth in SEQ ID NO: 30, and wherein said SHRR comprises an amino acid sequence having at least about 90% sequence identity to the amino acid sequence set forth in SEQ ID NO: 31. The herein provided chimeric polypeptides comprise an RSV fusion protein (or a fragment thereof) which is to be stabilized in the pre-fusion conformation by a structure-stabilizing moiety. Such chimericpolypeptides are particularly useful as antigens, inter alia, in the immunization and / or vaccination of asubject against RSV. While the use of RSV fusion protein antigens as vaccines has been proposed in the art, it has surprisingly been found in the context of the present invention that the chimeric polypeptides according to the invention exhibit a range of properties that render them outstandingly advantageous for medical use, particularly for the vaccination / immunization against RSV. Thus, as also described in the appended examples and figures, it has been surprisingly found that the herein provided chimeric polypeptides: -can be efficiently produced (i.e., their production results in advantageously high yield) andpurified (see also Figures 1, 2, and 6, and Examples 2, 3, and 6),- are advantageously stable over several months (such as, e.g., for at least 6 months at 2-8 °C orfor at least 12 months at 2-8 °C) without the need for lyophilization thereof and / or at high temperatures (such as, e.g., at exposure to 25 °C or 40 °C for at least one week) (see also Figures3, 4, 6, 7, and 11 and Examples 5 and 6),- form a (desired) trimer conformation that is particularly effective, inter alia, for theimmunization of a subject against RSV (see also Figure 4 and Example 5),- comprise the RSV fusion protein in the (desired) pre-fusion conformation, which is particularlyadvantageous for medical applications such as the immunization and / or vaccination of a subject against RSV (see also Table 5 and Example 4),- have an advantageously high binding affinity to known anti-RSV fusion protein antibodies (seealso Table 5, Figure 5, and Example 4),- allow the formation of advantageously high antibody titers when administered to a subject (seealso Figure 8 and Example 6), in particular approx.2-fold higher neutralization immune responseas compared to the dose-matched commercially available Arexvy antigen, and -demonstrated in a phase 1 clinical trial:o desirable safety and reactogenicity (Tables 7 to 10, and Example 9),o particularly desirable induction of neutralizing antibodies against RSV A and B strains(Figure 12 and Example 9),o surprisingly high titers of neutralizing antibodies that exceeded those induced by thecommercially available RSV vaccine Arexvy (GSK; Figure 12 and Example 9).These advantageous properties were unexpected and render the chimeric polypeptides according to the present invention particularly well suited for pharmaceutical use, especially for the vaccination / immunization against RSV as well as the prevention (or prophylactic treatment) of an RSV infection. Accordingly, a vaccine comprising the herein provided antigen, in particular a chimericpolypeptide according to SEQ ID NO: 27, is currently being probed in clinical trials (see also Example 9).Moreover, the chimeric polypeptides provided herein have been found to exhibit remarkable advantages over antigens known from the state of the art, and even in comparison to hitherto best-in- class comparators, as also described and demonstrated in the appended examples and figures. In thisregard, the present inventors surprisingly found that, inter alia, the length of the C-terminus of the RSVfusion protein comprised in the chimeric polypeptides of the present invention can influence the above- mentioned characteristics. This is particularly remarkable as the C-terminus of the RSV fusion protein is covalently bound (or, in other words, connected / linked / coupled / fused), optionally via a linker, to the structure-stabilizing moiety. As such, the C-terminus is likely not comprised in an epitope to be bound by an antigen-binding molecule (such as an antibody) with specificity to an RSV fusion protein. The present inventors surprisingly found that a C-terminal amino acid sequence consisting of IRK (see, for example, the last three / the three C-terminal amino acids of the RSV fusion protein according to SEQ ID NO: 26, as comprised in the chimeric polypeptide S508) or IRR is particularly advantageous in the context of the present invention. The length and / or sequence of the C-terminal amino acids of the RSV fusion protein in accordance with the present invention differ from the reference polypeptide VXB-211 (SEQ ID NO: 25) and contribute to the advantageous characteristics (such as the stabilization of the pre-fusion conformation) of the chimeric polypeptides provided herein. In particular, Example 4 and Table 5show that VXB-211 shows poor binding to pre-fusion specific monoclonal antibodies (mAbs) as compared to the binding of the chimeric polypeptides according to the present invention (including in particular the preferred chimeric polypeptide S508), which is indicative of incorrect / undesired / non-pre- fusion folding and / or conformation of the reference polypeptide VXB-211. In contrast, the chimeric polypeptides in accordance with the present invention (as exemplified, for instance, in S508 / SEQ ID NO: 27) achieve consistent sub-nanomolar binding (i.e., high binding affinity, which is desired in the context of the present invention) to all tested antibodies, including all tested pre-fusion specific antibodies. In contrast thereto, SC910AY-509-CT5s (SEQ ID NO: 18) (which differs from S508 only in a single amino acid residue at the C-terminus of the RSV fusion protein) does not show sub-nanomolar binding to the tested antibodies. VXB-211 has been previously identified in WO 2023187743 A1 as VL22_CD11145T8 QS CT5 or VL22 CT5S, where it was shown to produce a well-defined peak representative of trimer, have desired thermal stability, and stabilization of the pre-fusion conformation (as evidenced by the binding to pre- fusion specific antibody D25) and was therefore advanced as potential clinical candidate. Thus, overall VXB 211 showed desirable characteristics. Yet, the present inventors found non-optimal binding of VXB- 211 to prefusion specific antibody AM14 and therefore aimed at providing even further improved antigens (such as S508 in SEQ ID NO: 27). The chimeric polypeptide provided in the first aspect of the present invention may comprise a respiratory syncytial virus (RSV) fusion protein and a structure-stabilizing moiety, wherein said RSV fusion protein comprises an amino acid sequence having, with an increasing degree of preference, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, about 100%, or 100% sequence identity to the amino acid sequence set forth in SEQ ID NO: 26, wherein said RSV fusion protein comprises a C-terminal amino acid sequence consisting of the amino acid sequence IRK or IRR (preferably IRK), wherein said structure-stabilizing moiety comprises a first heptad repeat region (FHRR) and a second heptad repeat region (SHRR), wherein said FHRR comprises an amino acid sequence having, with an increasing degree of preference, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, about 100%, or 100% sequence identity to the amino acid sequence set forth in SEQ ID NO: 30, and wherein said SHRR comprises an amino acid sequence having, with an increasing degree of preference, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, about 100%, or 100% sequence identity to the amino acid sequence set forth in SEQ ID NO: 31. The RSV fusion protein comprised in the chimeric polypeptide according to the invention may also be referred to as RSV fusion protein moiety. In the context of the present invention, higher percentages of sequence identities are preferred. For example: “about 100% sequence identity” is preferred over “at least about 99% sequence identity”, which, in turn, is preferred over “at least about 98% sequence identity”, etc. In this context, the disclosure of a certain sequence identity percentage (such as, e.g., “at least about 90% sequence identity”) also herein implies the disclosure of any higher (i.e., more preferred) sequence identity percentage (such as, e.g., “at least about 90% sequence identity”, “at least about 91% sequence identity”, “at least about 92% sequence identity”, “at least about 93% sequence identity”, “at least about 94% sequence identity”, “at least about 95% sequence identity”, “at least about 96% sequence identity”, “at least about 97% sequence identity”, “at least about 98% sequence identity”, “at least about 99% sequence identity”, or “about 100% sequence identity”). The same applies to other ranges (such as in the context of trimer formation) detailed herein below. The RSV fusion protein as well as the FHRR and the SHRR are each defined herein above by a percent sequence identity to a specific reference sequence. While the sequence identity for each one of these moieties (the RSV fusion protein, the FHRR, and the SHRR) can, in principle, be selected independently from the sequence identity for any of the other moieties, it is generally preferred that the same percent values / thresholds are selected for the sequence identity of the RSV fusion protein, the sequence identity of the FHRR, and the sequence identity of the SHRR. When an amino acid sequence is indicated herein to allow for a certain percentage of sequence variability (such as, e.g., “an amino acid sequence having at least about 90% sequence identity”, which allows for about 10% sequence variability), it is preferred that such sequence variability arises through conservative amino acid substitutions. In a preferred embodiment, the herein provided chimeric polypeptide comprises a respiratory syncytial virus (RSV) fusion protein and a structure-stabilizing moiety, wherein said RSV fusion protein consists of an amino acid sequence having, with an increasing degree of preference, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, about 100%, or 100% sequence identity to the amino acid sequence set forth in SEQ ID NO: 26, wherein said RSV fusion protein comprises a C-terminal amino acid sequence consisting of the amino acid sequence IRK or IRR (preferably IRK), wherein said structure-stabilizing moiety comprises a first heptad repeat region (FHRR) and a second heptad repeat region (SHRR), wherein said FHRR consists of an amino acid sequence having, with an increasing degree of preference, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, about 100%, or 100% sequence identity to the amino acid sequence set forth in SEQ ID NO: 30, and wherein said SHRR consists of an amino acid sequence having, with an increasing degree of preference, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, about 100%, or 100% sequence identity to the amino acid sequence set forth in SEQ ID NO: 31. It is furthermore preferred that the chimeric polypeptide comprises, in N- to C-terminal order (i.e., from the N-terminus to the C-terminus of the chimeric polypeptide), the RSV fusion protein and thereafter the structure-stabilizing moiety. Accordingly, it is preferred that the C-terminus of the RSV fusion protein is connected, optionally via a linker, to the N-terminus of the structure-stabilizing moiety. Moreover, it is preferred that the structure-stabilizing moiety (which is comprised in the chimeric polypeptide) comprises, in N- to C-terminal order, the FHRR and the SHRR. Thus, it is preferred that the C-terminus of the FHRR is connected, optionally via a linker, to the N-terminus of the SHRR. In general, unless explicitly stated otherwise, the order in which the different moieties comprised in the chimeric polypeptide according to the invention are mentioned (within any sentence in the present specification) corresponds to the specific N- to C-terminal order in which these moieties are preferably present. The inventors have introduced various modifications / amino acid substitutions / mutations (apart from the above-mentioned modification of the C-terminus) in the wildtype (backbone of the) RSV fusion protein of RSV strain A2 (the respective wildtype fusion protein is shown in SEQ ID NO: 1). Such modifications include, for example, the deletion of a transmembrane domain and a cytoplasmic domain (see SEQ ID NO: 1), thereby resulting in the production of a non-membrane-bound RSV fusion protein. Such ‘non-membrane-bound’ RSV fusion proteins may also be termed ‘soluble’ RSV fusion proteins, or the like. Further, the present inventors have replaced an amino acid stretch comprising furin cleavage sites in the RSV wildtype backbone with a flexible linker. Said flexible linker corresponds to the amino acid sequence “GS” in positions 81 to 82 of SEQ ID NO 26. However, in the context of the present invention, such flexible linkers are not particularly limited. Suitable flexible peptide linkers are well known in the art and are further detailed herein below. Accordingly, in the context of the present invention, also alternative flexible linkers (replacing the amino acid sequence “GS” in positions 81 to 82 of SEQ ID NO 26) are envisaged and can be used. Such flexible linkers may include, for example, any one or more of: GSG, GGSGG (SEQ ID NO: 32), GGSG (SEQ ID NO: 33), GSGS (SEQ ID NO: 34), AS, GGGS (SEQ ID NO: 35), G4S (SEQ ID NO: 36), (G4S)2 (SEQ ID NO: 37), (G4S)3 (SEQ ID NO: 38), (G4S)4 (SEQ ID NO: 39), G4SG (SEQ ID NO: 40), GSGG (SEQ ID NO: 41), and GSGGS (SEQ ID NO: 42). However, also any combination of such flexible linkers is herein envisaged. It is further envisaged that such flexible linkers may be absent (i.e., that the amino acid sequence “GS” in positions 81 to 82 of SEQ ID NO 26 is absent / deleted). The present inventors have further substituted / replaced several amino acid residues in the RSV fusion protein comprised in the chimeric polypeptide. Such amino acid substitutions are further summarized in Example 1. It has been shown in the appended examples that such amino acid substitutions (as alsocomprised in the SC9-10 DSCav1AY RSV fusion protein backbone; see also McLellan, Chen et al. 2013,which is herein incorporated by reference in its entirety), when used in the chimeric polypeptides according to the invention, contribute to the above-mentioned advantageous effects (such as, for example, an improved yield). Accordingly, in the context of the first aspect of the invention, the RSV fusion protein (comprised in the chimeric polypeptide) may comprise any one or more, preferably all, of the following amino acid residues:(i) a cysteine residue in position 87 in the amino acid sequence set forth in SEQ ID NO: 26 or at aposition corresponding to said position;(ii) a cysteine residue in position 93 in the amino acid sequence set forth in SEQ ID NO: 26 or at aposition corresponding to said position; (iii) a phenylalanine residue in position 128 in the amino acid sequence set forth in SEQ ID NO: 26 or at a position corresponding to said position; (iv) a leucine residue in position 145 in the amino acid sequence set forth in SEQ ID NO: 26 or at a position corresponding to said position;(v) a cysteine residue in position 228 in the amino acid sequence set forth in SEQ ID NO: 26 or at aposition corresponding to said position; (vi) an arginine residue in position 311 in the amino acid sequence set forth in SEQ ID NO: 26 or at a position corresponding to said position; and (vii) a cysteine residue in position 396 in the amino acid sequence set forth in SEQ ID NO: 26 or at a position corresponding to said position. Said cysteine residues (of (i), (ii), (v), and (vii), above) may preferably form disulfide bridges. In particular, it is preferred that the cysteine residue in position 87 in the amino acid sequence set forth in SEQ ID NO: 26 or at a position corresponding to said position forms / is capable of forming a disulfide bridge with the cysteine residue in position 396 in the amino acid sequence set forth in SEQ ID NO: 26 or at a position corresponding to said position. Further, it is preferred that the cysteine residue in position 93 in the amino acid sequence set forth in SEQ ID NO: 26 or at a position corresponding to said position forms / is capable of forming a disulfide bridge with the cysteine residue in position 228 in the amino acid sequence set forth in SEQ ID NO: 26 or at a position corresponding to said position. The skilled person is aware of, e.g., conditions / buffers / buffer systems / the like that allow for the formation of disulfide bridges. It will be understood that, in principle, disulfide bridges may be intramolecular disulfide bridges or intermolecular disulfide bridges. Intramolecular / intrachain disulfide bridges are formed between two cysteine residues comprised in the same molecule (i.e., the same polypeptide chain) whereas intermolecular / interchain disulfide bridges are typically formed between two cysteine residues comprised in two different molecules (i.e., two different polypeptide chains), such as, in particular, between two identical polypeptides (i.e., two polypeptides with identical amino acid sequence). The above-mentioned disulfide bridge between the cysteine residues in positions 87 and 396 (of, e.g., SEQ ID NO: 26), or between cysteine residues in positions corresponding to these positions, is preferably an intermolecular / interchain disulfide bridge. The above-mentioned disulfide bridge between the cysteine residues in positions 93 and 228 (of, e.g., SEQ ID NO: 26), or between cysteine residues in positions corresponding to these positions, is preferably an intramolecular / intrachain disulfide bridge. Preferably, the chimeric polypeptide comprises an RSV fusion protein comprising the amino acid sequence set forth in SEQ ID NO: 26. More preferably, the chimeric polypeptide comprises an RSV fusion protein consisting of the amino acid sequence set forth in SEQ ID NO: 26. The FHRR and the SHRR comprised in the structure-stabilizing moiety are preferably linked via a linker, wherein said linker is preferably a peptide linker. Such linkers (or peptide linkers) are not particularly limited in the context of the present invention, as long as they allow for the flexible linkage / coupling of said FHRR and said SHRR. Such linkers may comprise (or, preferably, consist of) an amino acid sequence selected from GGSGG (SEQ ID NO: 32), GSG, GS, GGSG (SEQ ID NO: 33), GSGS (SEQ ID NO: 34), AS, GGGS (SEQ ID NO: 35), G4S (SEQ ID NO: 36), (G4S)2 (SEQ ID NO: 37), (G4S)3 (SEQ ID NO: 38), (G4S)4 (SEQ ID NO: 39), G4SG (SEQ ID NO: 40), GSGG (SEQ ID NO: 41), and GSGGS (SEQ ID NO: 42). As mentioned above, also any combination of such linkers (e.g., a combination of any two or three of the aforementioned linkers) is herein envisaged. It is further envisaged herein that such linkers may be absent (e.g., that the C-terminus of the FHRR is directly coupled / linked to the N-terminus of the SHRR). Preferably, the C- terminus of the FHRR is linked to the N-terminus of the SHRR via a linker comprising (or, preferably, consisting of) the amino acid sequence GGSGG (SEQ ID NO: 32). Accordingly, it is preferred that the structure-stabilizing moiety comprises: (i) an FHRR comprising (or, preferably, consisting of) an amino acid sequence having, with an increasing degree of preference, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, about 100%, or 100% sequence identity to the amino acid sequence set forth in SEQ ID NO: 30; (ii) an SHRR comprising (or, preferably, consisting of) an amino acid sequence having, with an increasing degree of preference, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, about 100%, or 100% sequence identity to the amino acid sequence set forth in SEQ ID NO: 31; and (iii) a linker linking the C-terminus of said FHRR to the N-terminus of said SHRR, wherein said linker preferably comprises (or, more preferably, consists of) the amino acid sequence GGSGG (SEQ ID NO: 32). Accordingly, it is particularly preferred that the structure-stabilizing moiety comprises (or, more preferably, consists of) an amino acid sequence having, with an increasing degree of preference, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, about 100%, or 100% sequence identity to the amino acid sequence set forth in SEQ ID NO: 29. Even more preferably, the structure-stabilizing moiety comprises the amino acid sequence set forth in SEQ ID NO: 29. Yet even more preferably, the structure-stabilizing moiety consists of the amino acid sequence set forth in SEQ ID NO: 29. A structure-stabilizing moiety consisting of the amino acid sequence set forth in SEQ ID NO: 29 is also referred to herein as “molecular clamp 2 silenced”, “MC2S”, “MC2S SSM”, or “CT5S”. This structure-stabilizing moiety is further described in WO 2023 / 187743 (where it is referred to as “clamp2s”), which is incorporated herein by reference in its entirety. The structure-stabilizing moiety may also be post-translationally modified, for example by glycosylation, as also described, e.g., in WO 2023 / 187743. Such glycosylation may reduce the immunogenicity (i.e., the reactivity to an immune system / non-self-recognition / elicitation of an immune response) of the SSM. Accordingly, in the context of the present invention, the structure-stabilizing moiety preferably comprises at least one immune-silencing moiety that reduces or inhibits elicitation of an immune response to the structure-stabilizing moiety, preferably wherein the immune silencing moiety is a glycosylation site. Thus, the structure-stabilizing moiety may comprise at least one glycosylation site, preferably wherein the at least one glycosylation site is an N-linked glycosylation site selected from:(i) -Asn-Xaa-Ser-; and(ii) -Asn-Xaa-Thr-;wherein Xaa is an amino acid other than Pro; preferably wherein the glycosylation site is glycosylated with an occupancy level of at least 50%. In particular, the structure-stabilizing moiety may comprise one or more N-linked glycosylation sites, e.g., at the amino acid positions corresponding to:(i) positions 5-7 of SEQ ID NO: 30;(ii) positions 1-3 of SEQ ID NO: 31; (iii) positions 6-8 of SEQ ID NO: 31; (iv) positions 13-15 of SEQ ID NO: 31; (v) positions 17-19 of SEQ ID NO: 31; and / or (vi) positions 27-29 of SEQ ID NO: 31; wherein preferably each N-linked glycosylation site is independently -Asn-Xaa-Thr-, wherein Xaa is an amino acid other than Pro. The structure-stabilizing moiety may comprise N-linked glycosylation sites at the amino acid positions corresponding to:(i) (i-a) positions 5-7 of SEQ ID NO: 30;(i-b) positions 1-3 of SEQ ID NO: 31; and (i-c) positions 17-19 of SEQ ID NO: 31; or (ii) (ii-a) positions 5-7 of SEQ ID NO: 30; (ii-b) positions 1-3 of SEQ ID NO: 31; (ii-c) positions 17-19 of SEQ ID NO: 31; and (ii-d) positions 27-29 of SEQ ID NO: 31; or (iii) (iii-a) positions 5-7 of SEQ ID NO: 30; (iii-b) positions 1-3 of SEQ ID NO: 31; (iii-c) positions 13-15 of SEQ ID NO: 31; (iii-d) positions 17-19 of SEQ ID NO: 31; and (iii-e) positions 27-29 of SEQ ID NO: 31; or (iv) (iv-a) positions 5-7 of SEQ ID NO: 30; (iv-b) positions 1-3 of SEQ ID NO: 31; (iv-c) positions 6-8 of SEQ ID NO: 31; (iv-d) positions 13-15 of SEQ ID NO: 31; (iv-e) positions 17-19 of SEQ ID NO: 31; and (iv-f) positions 27-29 of SEQ ID NO: 31; wherein preferably each N-linked glycosylation site is independently -Asn-Xaa-Thr-, wherein Xaa is an amino acid other than Pro. If the SSM comprises one or more glycosylation site(s), it is preferred that said one or more glycosylation site(s) are comprised in said SHRR. Accordingly, it is preferred that the SHRR (as comprised in the SSM) comprises one or more N-linked glycosylation site(s) at any one or more of amino acid positions corresponding to: (i) positions 1-3 of SEQ ID NO: 31; (ii) positions 13-15 of SEQ ID NO: 31; (iv) positions 17-19 of SEQ ID NO: 31; and (v) positions 27-29 of SEQ ID NO: 31; wherein preferably each N-linked glycosylation site is independently -Asn-Xaa-Thr-, wherein Xaa is an amino acid other than Pro. More preferably, the SHRR (as comprised in the SSM) comprises an N-linked glycosylation site at amino acid positions corresponding to: (i) positions 1-3 of SEQ ID NO: 31; (ii) positions 13-15 of SEQ ID NO: 31; (iv) positions 17-19 of SEQ ID NO: 31; and (v) positions 27-29 of SEQ ID NO: 31; wherein preferably each N-linked glycosylation site is independently -Asn-Xaa-Thr-, wherein Xaa is an amino acid other than Pro. Even more preferably, the SHRR (as comprised in the SSM) comprises an N-linked glycosylation site at amino acid positions corresponding to: (i) positions 1-3 of SEQ ID NO: 31, with said N-linked glycosylation site consisting of NHT; (ii) positions 13-15 of SEQ ID NO: 31, with said N-linked glycosylation site consisting of NHT; (iv) positions 17-19 of SEQ ID NO: 31, with said N-linked glycosylation site consisting of NLT; and (v) positions 27-29 of SEQ ID NO: 31, with said N-linked glycosylation site consisting of NQT. The present invention also envisages non-silenced structure-stabilizing moieties, i.e., structure stabilizing moieties not comprising immune-silencing moieties (e.g., glycosylation sited), however, herein preferred are silenced structure-stabilizing moieties as detailed herein above. Accordingly, the herein provided chimeric polypeptide may also comprise a structure-stabilizing moiety comprising: (i) an FHRR comprising (or, preferably, consisting of) an amino acid sequence having, with an increasing degree of preference, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, about 100%, or 100% sequence identity to the amino acid sequence set forth in SEQ ID NO: 43; (ii) an SHRR comprising (or, preferably, consisting of) an amino acid sequence having, with an increasing degree of preference, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, about 100%, or 100% sequence identity to the amino acid sequence set forth in SEQ ID NO: 44; and (iii) a linker linking the C-terminus of said FHRR to the N-terminus of said SHRR, wherein said linker preferably comprises (or, more preferably, consists of) the amino acid sequence GGSGG (SEQ ID NO: 32). Accordingly, the structure-stabilizing moiety may comprise (or, preferably, consists of) an amino acid sequence having, with an increasing degree of preference, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, about 100%, or 100% sequence identity to the amino acid sequence set forth in SEQ ID NO: 45. Even preferably, the structure-stabilizing moiety comprises the amino acid sequence set forth in SEQ ID NO: 45. Yet more preferably, the structure-stabilizing moiety consists of the amino acid sequence set forth in SEQ ID NO: 45. The structure stabilizing moiety according to SEQ ID NO: 45 may herein also be referred to as “MC2” or “MC2 SSM” or the like. This structure-stabilizing moiety is further described in WO 2023 / 187743 (where it is referred to as “clamp2”). Accordingly, the chimeric polypeptide may preferably comprise (or, more preferably, consist of) an amino acid sequence having, with an increasing degree of preference, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, about 100%, or 100% sequence identity to the amino acid sequence set forth in SEQ ID NO: 46. Accordingly, the chimeric polypeptide may preferably consist of an amino acid sequence set forth in SEQ ID NO: 46. Accordingly, the chimeric polypeptide may preferably comprise (or, more preferably, consist of) an amino acid sequence having, with an increasing degree of preference, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, about 100%, or 100% sequence identity to the amino acid sequence set forth in SEQ ID NO: 47. Accordingly, the chimeric polypeptide may preferably consist of an amino acid sequence set forth in SEQ ID NO: 47. In the context of the chimeric polypeptide provided herein, the RSV fusion protein and the structure- stabilizing moiety may be linked via a linker, preferably wherein said linker is a peptide linker. Said linker may comprise (or, preferably, consists of) an amino acid sequence selected from GSG, GS, GGSGG (SEQ ID NO: 32), GGSG (SEQ ID NO: 33), GSGS (SEQ ID NO: 34), AS, GGGS (SEQ ID NO: 35), G4S (SEQ ID NO: 36), (G4S)2 (SEQ ID NO: 37), (G4S)3 (SEQ ID NO: 38), (G4S)4 (SEQ ID NO: 39), G4SG (SEQ ID NO: 40), GSGG (SEQ ID NO: 41), and GSGGS (SEQ ID NO: 42). However, also any combination of such flexible linkers is herein envisaged. It is further envisaged herein that such flexible linkers may be absent (e.g., that the C-terminus of the RSV fusion protein is linked / coupled directly to the N-terminus of the structure- stabilizing moiety). Preferably, the C-terminus of said RSV fusion protein is linked / coupled to the N- terminus of said structure-stabilizing moiety via a linker, wherein said linker comprises (or, more preferably, consists of) the amino acid sequence GSG. In a preferred embodiment, the first aspect of the present invention provides a chimeric polypeptide comprising a respiratory syncytial virus (RSV) fusion protein and a structure-stabilizing moiety, wherein said RSV fusion protein comprises (or, preferably, consists of) an amino acid sequence having, with an increasing degree of preference, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, about 100%, or 100% sequence identity to the amino acid sequence set forth in SEQ ID NO: 26, wherein said RSV fusion protein comprises a C-terminal amino acid sequence consisting of the amino acid sequence IRK (i.e., Ile-Arg-Lys) or IRR (i.e., Ile-Arg-Arg), preferably IRK, wherein said structure-stabilizing moiety comprises a first heptad repeat region (FHRR) and a second heptad repeat region (SHRR), wherein said FHRR comprises (or, preferably, consists of) an amino acid sequence having, with an increasing degree of preference, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, about 100%, or 100% sequence identity to the amino acid sequence set forth in SEQ ID NO: 30, wherein said SHRR comprises (or, preferably, consists of) an amino acid sequence having, with an increasing degree of preference, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, about 100%, or 100% sequence identity to the amino acid sequence set forth in SEQ ID NO: 31, wherein said FHRR is linked to said SHRR via a linker, and wherein said RSV fusion protein is linked to said structure-stabilizing moiety via a linker. In a preferred embodiment, the first aspect of the present invention provides a chimeric polypeptide comprising a respiratory syncytial virus (RSV) fusion protein and a structure-stabilizing moiety, wherein said RSV fusion protein comprises (or, preferably, consists of) an amino acid sequence having, with an increasing degree of preference, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, about 100%, or 100% sequence identity to the amino acid sequence set forth in SEQ ID NO: 26, wherein said RSV fusion protein comprises a C-terminal amino acid sequence consisting of the amino acid sequence IRK or IRR (preferably IRK), wherein said structure-stabilizing moiety comprises a first heptad repeat region (FHRR) and a second heptad repeat region (SHRR), wherein said FHRR comprises (or, preferably, consists of) an amino acid sequence having, with an increasing degree of preference, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, about 100%, or 100% sequence identity to the amino acid sequence set forth in SEQ ID NO: 30, wherein said SHRR comprises (or, preferably, consists of) an amino acid sequence having, with an increasing degree of preference, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, about 100%, or 100% sequence identity to the amino acid sequence set forth in SEQ ID NO: 31, wherein said FHRR is linked to said SHRR via a linker comprising (or, preferably, consisting of) the amino acid sequence GGSGG (SEQ ID NO: 32), and wherein said RSV fusion protein is linked to said structure-stabilizing moiety via a linker comprising (or, preferably, consisting of) the amino acid sequence GSG. In a preferred embodiment, the herein provided chimeric polypeptide comprises an amino acid sequence having, with an increasing degree of preference, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, about 100%, or 100% sequence identity to the amino acid sequence set forth in SEQ ID NO: 27. In a particularly preferred embodiment, the chimeric polypeptide comprises (or consists of) the amino acid sequence set forth in SEQ ID NO: 27.As also shown in Example 5 and Figure 4, the chimeric polypeptides according to the invention (asexemplified by “S508” in Figure 4) are primarily forming / adopting a (desired) (homo-)trimericpolypeptide complex (as opposed to monomers or aggregates). A “homotrimeric polypeptide complex” consists of three identical polypeptide subunits, such as of three identical chimeric polypeptides. In this context, it is preferred that the FHRRs and SHRRs of the three SSMs are associated in the form of a six-helix bundle. The term “helix bundle” refers to a plurality of peptide helices that fold such that the helicesare substantially parallel or anti-parallel to one another. A two-helix bundle has two helices folded such that they are substantially parallel or anti-parallel to one another. Likewise, a six-helix bundle has six helices folded such that they are substantially parallel or anti-parallel to one another. By “substantially parallel or anti-parallel” it is meant that the helices are folded such that the side chains of the helices are able to interact with one another. For example, the hydrophobic side chains of the helices are able to interact with one another to form a hydrophobic core. Figure 4 illustrates that about 89% to about 94% of a chimeric polypeptide according to the invention form a trimer, whereas only about 57% to about 69% of reference chimeric polypeptides (i.e., SC9-10 SDCaVAY and DsCav1Fd) form a trimer. Accordingly, it is preferred that at least about 70%, at least about 75%, at least about 80%, at least about 81%, at least about 82%, at least about 83%, at least about 84%, at least about 85%, at least about 86%, at least about 87%, at least about 88%, or at least about 89% of the chimeric polypeptide is in the form of a (homo-)trimer. The aforementioned percentages relate to weight-% or mol-%, preferably to weight-%. As explained above, viral fusion proteins can be present in a pre-fusion and a post-fusion state / conformation. It is desired in the context of the present invention that the chimeric fusionpolypeptides (largely) remain in the pre-fusion state / conformation. As illustrated in Example 4 andTable 5, the chimeric polypeptide of the invention (as exemplified by SC910AY-508-CT5s) has an advantageously low dissociation constant (kD) when contacted with an anti-RSV fusion protein antibody that is specific / has substrate specificity for an RSV fusion protein in pre-fusion conformation (such as the antibodies D25 and AM14). This indicates that the herein provided chimeric polypeptides adopt the desired pre-fusion conformation. Accordingly, it is preferred that the RSV fusion protein comprised in the chimeric polypeptide adopts / is present in the pre-fusion conformation. When present in the prefusion conformation antigens are particularly suitable for eliciting neutralizing immune responses / inducing production of neutralizing antibodies. The enclosed examples illustrate that the induction of such neutralizing immune responses after administration of S508 (see in particularFigure 8). Further, Figure 10 illustratively demonstrates that the herein provided chimeric polypeptidesare highly efficient in depleting neutralizing antibodies. Accordingly, it is preferred that the herein provided chimeric polypeptides are capable of inducing a neutralizing immune response. It will be understood that the chimeric polypeptides may further comprise an N-terminal signal sequence or signal peptide that may determine the localization of the chimeric polypeptide when expressed in a host cell. Suitable signal peptides are known in the art. In the context of the present invention, a preferred signal peptide comprises (or, preferably, consists of) an amino acid sequence having, with an increasing degree of preference, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, about 100%, or 100% sequence identity to SEQ ID NO: 28. More preferably, the signal peptide comprises (or, even more preferably, consists of) the amino acid sequence set forth in SEQ ID NO: 28. Accordingly, the RSV fusion protein comprised in the chimeric polypeptide may further comprise an N-terminal signal peptide, preferably wherein said signal peptide comprises (or, more preferably, consists of) an amino acid sequence having, with an increasing degree of preference, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, about 100%, or 100% sequence identity to SEQ ID NO: 28. More preferably, the signal peptide comprises (or, even more preferably, consists of) the amino acid sequence set forth in SEQ ID NO: 28. SEQ ID NO: 27 illustrates an exemplary, particularly preferred embodiment of the chimeric polypeptide lacking a signal peptide. SEQ ID NO: 17 comprises an N-terminal signal peptide according to SEQ ID NO: 28 which is linked to the exemplary chimeric polypeptide of SEQ ID NO: 27. Accordingly, the chimeric polypeptide may comprise (or consists of) an amino acid sequence having, with an increasing degree of preference, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, about 100%, or 100% sequence identity to the amino acid sequence set forth in SEQ ID NO: 17. In a preferred embodiment, the chimeric polypeptide comprises (or, more preferably, consists of) the amino acid sequence set forth in SEQ ID NO: 17. As explained herein, the chimeric polypeptides are particularly advantageous for use in the immunization and / or vaccination of a subject (against RSV). It will be understood that the chimeric polypeptides preferably do not comprise a signal peptide when employed for medical use, particularly in the immunization and / or vaccination of a subject. In contrast, when a nucleic acid encoding the chimeric polypeptide is employed for medical use, e.g., for the immunization and / or vaccination of a subject, or for expression in a host cell, the presence of an N-terminal signal peptide (such as, e.g., the signal peptide exemplified in SEQ ID NO: 28) in the encoded polypeptide is preferred. As explained above, the RSV fusion protein (comprised in the chimeric polypeptide according to the first aspect of the invention) comprises a C-terminal amino acid sequence consisting of the amino acid sequence IRK or IRR, preferably consisting of the amino acid sequence IRK. In the present specification, various specific / exemplary sequences comprising the aforementioned amino acid sequence IRK are described, including, e.g., the sequence set forth in SEQ ID NO: 26, the sequence set forth in SEQ ID NO: 27, and the sequence set forth in SEQ ID NO: 17. It is to be understood that the present invention also relates to sequences corresponding to SEQ ID NO: 26, SEQ ID NO: 27 and SEQ ID NO: 17, respectively, but differing from these sequences in that they comprise the sequence IRR instead of the sequence IRK. In line with this, all passages of the present specification that make reference to any of SEQ ID NO: 26, SEQ ID NO: 27 or SEQ ID NO: 17 are to be understood as also making reference to the respective sequence wherein the amino acid sequence IRK is replaced by IRR, and preferably as making reference to the corresponding explicitly mentioned sequence (comprising the amino acid sequence IRK). Accordingly, the present invention relates, in particular, to (i) a chimeric polypeptide comprising an amino acid sequence having at least about 90% sequence identity to the amino acid sequence set forth in SEQ ID NO: 27, (ii) a chimeric polypeptide comprising an amino acid sequence having at least about 90% sequence identity to the amino acid sequence set forth in SEQ ID NO: 27 wherein the sequence IRK comprised in SEQ ID NO: 27 is replaced by IRR, or (iii) a composition comprising both the aforementioned chimeric polypeptides (i) and (ii). The invention further relates to (i) a chimeric polypeptide comprising (or, preferably, consisting of) the amino acid sequence set forth in SEQ ID NO: 27, (ii) a chimeric polypeptide comprising (or, preferably, consisting of) the amino acid sequence set forth in SEQ ID NO: 27 wherein the sequence IRK comprised in SEQ ID NO: 27 is replaced by IRR, or (iii) a composition comprising both the aforementioned chimeric polypeptides (i) and (ii). In a second aspect, the present invention provides a nucleic acid comprising a nucleic acid sequence encoding the chimeric polypeptide provided in the first aspect of the invention. The term “nucleic acid”, as used herein, encompasses any molecule containing two or more nucleotides, particularly a polymer of nucleotides, such as, e.g., a deoxyribonucleic acid (DNA) or a ribonucleic acid (RNA). The nucleotides may be, e.g., deoxyribonucleotides, ribonucleotides or nucleotide analogues, and they may optionally be substituted or modified. The nucleotides can be linked by phosphodiester bonds / linkages or, e.g., by phosphorothioate linkages, methylphosphonate linkages or boranophosphate linkages. The term “nucleic acid” particularly relates to DNA or RNA, such as, e.g., mRNA, cRNA, or cDNA. The term typically refers to polymeric forms of nucleotides of, e.g., at least 10 bases in length, either ribonucleotides or deoxynucleotides or a modified form of either type of nucleotide. A “nucleic acid” can be single stranded or double stranded. Accordingly, the herein provided nucleic acid may be a ribonucleic acid (RNA), preferably a messenger RNA (mRNA). As will be detailed herein below, such nucleic acids (particularly mRNA) encoding the chimeric polypeptides of the invention are also particularly useful in the immunization and / or vaccination of a subject. As indicated herein above and below, the present invention provides for a complex comprising three subunits, wherein each subunit is a herein provided chimeric polypeptide. Preferably, the complex is characterized by a six-helix bundle formed by homo-trimerization of the structure-stabilizing moieties of the three chimeric polypeptides. Accordingly, it is preferred that the herein provided complex comprises three identical subunits (e.g., wherein each subunit is a chimeric polypeptide having an amino acid sequence set forth in SEQ ID NO: 27). The present invention further provides for a method of producing a chimeric polypeptide complex, wherein the method comprises: combining chimeric polypeptides as defined in accordance with the first aspect of the invention under conditions suitable for the formation of a chimeric polypeptide complex, whereby a chimeric polypeptide complex is produced that comprises three chimeric polypeptide subunits and is preferably characterized by a six-helix bundle formed by homo-trimerization of the structure-stabilizing moieties of the three chimeric polypeptides. In a third aspect, the present invention provides a composition comprising the chimeric polypeptide (according to the first aspect) or the nucleic acid encoding the chimeric polypeptide (according to the second aspect), preferably wherein said composition is a pharmaceutical composition. The composition according to the third aspect may also (i.e., additionally, or alternatively to the chimeric polypeptide or the nucleic acid) comprise the herein provided complex. Optionally, said composition may further comprise a pharmaceutically acceptable carrier, diluent and / or adjuvant. In the context of a composition comprising an mRNA encoding a chimeric polypeptide, it is preferred that the pharmaceutically acceptable carrier is a lipid nanoparticle (LNP) or that the composition is formulated as an LNP encapsulating the mRNA. The composition (or pharmaceutical composition) according to the third aspect may be an aqueous pharmaceutical composition, particularly an aqueous pharmaceutical composition comprising a buffer (or buffer system) and optionally a surfactant. Preferably, said buffer (or buffer system) is phosphate buffered saline (PBS). The surfactant may be, e.g., polysorbate 80. The composition (or pharmaceutical composition) can also be provided as a powder for reconstitution (e.g., to form an aqueous pharmaceutical composition, as described above, after reconstitution). A single dose of the composition may contain, e.g., an amount of about 10 µg to about 500 µg, preferably about 20 µg to about 300 µg, more preferably about 30 µg to about 240 µg (such as, in particular, about 30 µg, about 60 µg, about 120 µg, or about 240 µg), of the chimeric polypeptide. The composition (or pharmaceutical composition) may further comprise one or more other antigens (e.g., other viral antigens), particularly one or more antigens of (an)other respiratory virus(es) (i.e., other than RSV). For example, the composition may further comprise any one or more (e.g., one, two, three, four, five, six, or seven) antigen(s) selected from one or more antigen(s) of human metapneumovirus (hMPV), one or more antigen(s) of human parainfluenza virus (hPIV; e.g., hPIV-1, hPIV-2, hPIV-3, and / or hPIV-4), one or more antigen(s) of an influenza virus (particularly a human influenza virus; e.g., influenza A H1N1, influenza A H3N2, and / or influenza B), one or more antigen(s) of a coronavirus (particularly a human coronavirus; e.g., SARS-CoV-2), and / or one or more antigen(s) of other human respiratory viruses. Preferably, said one or more antigen(s) is / are antigen(s) comprising a viral fusion protein (i.e., a fusion protein antigen) of the respective virus. In particular, the composition may further comprise an antigen of hMPV and / or an antigen of hPIV, particularly an hMPV fusion protein antigen and / or an hPIV (particularly hPIV-3) fusion protein antigen. A corresponding composition comprising one further antigen may be used as a bivalent vaccine (e.g., a bivalent vaccine against RSV and hMPV). A corresponding composition comprising two further antigens may be used as a trivalent vaccine (e.g., a trivalent vaccine against RSV, hMPV and hPIV). It is also envisaged herein that compositions comprising more than two (e.g., three, four, five, six, or seven) further antigens may be used as polyvalent vaccine (e.g., a polyvalent vaccine against RSV and three or more, preferably all, of hMPV, hPIV, influenza A H1N1, influenza A H3N2, influenza B, and SARS-CoV-2). Said composition may for example further comprise an hMPV-antigen comprising (or preferably consisting of) an amino acid sequence having, with an increasing degree of preference, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, about 100%, or 100% sequence identity to the amino acid sequence set forth in SEQ ID NO: 49. In a fourth aspect, the present invention provides a kit comprising the chimeric polypeptide (according to the first aspect), the nucleic acid (according to the second aspect), or the composition (according to the third aspect). The kit according to the fourth aspect may also (i.e., additionally, or alternatively to the chimeric polypeptide, the nucleic acid, or the composition) comprise the herein provided complex. In a fifth aspect, the present invention provides the chimeric polypeptide (according to the first aspect), the nucleic acid (according to the second aspect), the composition (according to the third aspect), or the kit (according to the fourth aspect), for use in the immunization and / or the vaccination of a subject. The present invention also provides for the herein provided complex for use in the immunization and / or the vaccination of a subject. Thus, the present invention provides the chimeric polypeptide (according to the first aspect), the nucleic acid (according to the second aspect), the composition (according to the third aspect), or the kit (according to the fourth aspect), for use in the immunization and / or the vaccination of a subject against a virus, particularly against RSV. The present invention also provides for the herein provided complex for use in the immunization and / or the vaccination of a subject against a virus, particularly against RSV. Accordingly, the present invention also provides the chimeric polypeptide (according to the first aspect), the nucleic acid (according to the second aspect), the composition (according to the third aspect), or the kit (according to the fourth aspect), for use as a vaccine against RSV or for use in the prevention (or prophylactic treatment) of an RSV infection (or a disease caused by an RSV infection). The present invention also provides for the herein provided complex for use as a vaccine against RSV or for use in the prevention (or prophylactic treatment) of an RSV infection (or a disease caused by an RSV infection). The present invention further provides a method for the immunization and / or the vaccination of a subject (preferably a human), particularly against RSV, wherein the method comprises administering the chimeric polypeptide (according to the first aspect), the nucleic acid (according to the second aspect), the composition (according to the third aspect), or the kit (according to the fourth aspect), to said subject. The present invention further provides a method for the immunization and / or the vaccination of a subject (preferably a human), particularly against RSV, wherein the method comprises administering the herein provided complex to said subject. It will be understood that an effective amount (particularly a pharmacologically effective amount) is to be administered to the subject in any such methods. The present invention further provides a method for the prevention of an RSV infection (or a disease caused by an RSV infection) in a subject (preferably a human), wherein the method comprises administering the chimeric polypeptide (according to the first aspect), the nucleic acid (according to the second aspect), the composition (according to the third aspect), or the kit (according to the fourth aspect), to said subject. The present invention also provides a method for the prevention of an RSV infection (or a disease caused by an RSV infection) in a subject (preferably a human), wherein the method comprises administering the herein provided complex to said subject. The present invention further provides the use of the chimeric polypeptide (according to the first aspect), the nucleic acid (according to the second aspect), or the composition (according to the third aspect) in the manufacture of a vaccine against RSV. The present invention also provides for the use of the herein provided complex in the manufacture of a vaccine against RSV. The present invention further provides the use of the chimeric polypeptide (according to the first aspect), the nucleic acid (according to the second aspect), or the composition (according to the third aspect) in the manufacture of a medicament for the prevention (or prophylactic treatment) of an RSV infection (or a disease caused by an RSV infection). The present invention further provides the use of the herein provided complex in the manufacture of a medicament for the prevention (or prophylactic treatment) of an RSV infection (or a disease caused by an RSV infection). In the context of the fifth aspect of the present invention, the subject is preferably a human (e.g., a male human or a female human). The subject may be, in particular, an adult human (e.g., a human at the age of 18 years or older), preferably a human of about 50 years or older, more preferably a human of about 55 years or older (e.g., about 56 years or older), even more preferably a human of about 60 years or older (including, e.g., about 65 years or older; about 66 years or older; about 70 years or older; about 75 years or older; about 76 years or older; or about 80 years or older). The subject may also be a pregnant (or gestating) female human (e.g., between weeks 24 and 36 of gestation). The immunization of pregnant women may be beneficial for the passive protection of newborn infants against RSV infections. Moreover, the subject may also be a human child (e.g., a human at the age of less than 18 years), particularly a human child of about 4 years or younger, or about 2 years or younger, or a human infant of about 1 year or younger, or about 6 months or younger. Further, the RSV infection may be, e.g., an infection with an RSV A strain (such as, for example, an RSV A2 strain) or an RSV B strain. Accordingly, said RSV may be, e.g., an RSV A strain or an RSV B strain. It will be understood that the RSV is particularly human RSV (hRSV), e.g., hRSV A and / or hRSV B. See alsoFigure 12 and Example 9, illustrating induction of desirable neutralizing antibody titers against bothRSV A and RSV B strains. In the context of the fifth aspect, it is preferred that an effective amount of the chimeric polypeptide, the nucleic acid, or the composition is to be administered to the subject. When the herein provided complex is to be administered to the subject in the context of the fifth aspect, it is also preferred that an effective amount thereof is to be administered. Typically, a physician will determine the specific amount / dosage that will be most suitable for an individual subject. The specific dose level and frequency of dosage for any particular subject may be varied and will depend upon a variety of factors, including the efficacy of the active agent employed, the metabolic stability and length of action of that agent, the mode and time of administration, and the age, body weight, general health and sex of the individual subject. A proposed, yet non-limiting dose of the chimeric polypeptide according to the invention for administration (e.g., for parenteral administration, particularly for intramuscular administration) to a human subject may be, e.g., about 10 µg to about 500 µg, preferably about 20 µg to about 300 µg, more preferably about 30 µg to about 240 µg (such as, in particular, about 30 µg, about 60 µg, about 120 µg, or about 240 µg), of the chimeric polypeptide per dose. A corresponding dose may be administered once, twice, three times, or more often. In particular, a single dose may be administered for immunization / vaccination of the subject. Further doses can be administered, particularly for revaccination or as booster / refresher, e.g., after a period of about 6 months to about 5 years (for example, after about 1 year). The chimeric polypeptide, the nucleic acid, or the composition can be administered to the subject by any convenient route of administration, including, but not limited to, the parenteral route, e.g., by intravenous, intramuscular, subcutaneous, or intradermal administration (e.g., injection). Alternatively, intranasal administration is also envisaged herein. A preferred route of administration is intramuscular administration (particularly intramuscular injection). The herein provided complex may be administered accordingly. In a sixth aspect, the present invention provides a nucleic acid vector comprising the nucleic acid (according to the second aspect). In a seventh aspect, the present invention provides a host cell comprising the nucleic acid (according to the second aspect) and / or the nucleic acid vector (according to the sixth aspect). In this context, it is preferred that the host cell is an isolated host cell, particularly an immortalized cell line (suitable for the production of biological products, such as polypeptides), more preferably a Chinese Hamster Ovary (CHO) cell line, a Human Embryonic Kidney (HEK) cell line, or an insect cell line (such as, e.g., SF9). A CHOcell line is herein preferred. Exemplary CHO cell lines include: CHO, ExpiCHO, CHO-S, CHO-K1, CHO-DG44 and CHO-DXB11. In an eighth aspect, the present invention provides a method of production of a chimeric polypeptide, wherein the method comprises:(i) culturing the host cell according to the seventh aspect; or(ii) expressing a chimeric polypeptide from the nucleic acid (according to the second aspect), and / orthe nucleic acid vector (according to the sixth aspect), optionally in a cell-free transcription-translation system. Said method may further comprise obtaining and / or purifying the chimeric polypeptide. In a ninth aspect, the present invention provides a method of production of an antigen-binding molecule (particularly an antibody) that specifically binds to an RSV fusion protein, the method comprising: (i) immunizing an animal (preferably a non-human mammal) with the chimeric polypeptide according the first aspect, or the nucleic acid according to the second aspect, or the composition according to the third aspect; (ii) identifying and / or isolating a B cell from the immunized animal, which specifically binds to the RSV fusion protein; and (iii) producing the antigen-binding molecule expressed by that B cell. Said method may further comprise obtaining and / or purifying the antigen-binding molecule. The present invention also provides a method of production of an antigen-binding molecule (particularly an antibody) that specifically binds to an RSV fusion protein, the method comprising: (i) immunizing an animal (preferably a non-human mammal) with the herein provided complex; (ii) identifying and / or isolating a B cell from the immunized animal, which specifically binds to the RSV fusion protein; and (iii) producing the antigen-binding molecule expressed by that B cell. Said method may further comprise obtaining and / or purifying the antigen-binding molecule.As shown in the appended examples (see, in particular, Example 4), the chimeric polypeptides adopt thedesired pre-fusion conformation. Accordingly, when employing the herein provided chimeric polypeptides, the herein provided nucleic acids, or the herein provided compositions in the method according to the ninth aspect, said method may preferably result in the production of an antigen-binding molecule (particularly an antibody) that specifically binds to an RSV fusion protein in the pre-fusion conformation and / or an antigen-binding molecule (particularly an antibody) that specifically binds to a complex (particularly a homotrimeric complex) of an RSV fusion protein in the pre-fusion conformation. In a tenth aspect, the present invention provides an antigen-binding molecule obtainable (or obtained) by the method according to the ninth aspect. Accordingly, said antigen-binding molecule is preferably an antigen-binding molecule that specifically binds to an RSV fusion protein in the pre-fusion conformation and / or an antigen-binding molecule that specifically binds to a (preferably homotrimeric) complex of an RSV fusion protein in the pre-fusion conformation. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present specification pertains. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, preferred methods and materials are described herein. The following definitions apply throughout the present specification and the claims, unless specifically indicated otherwise. As used herein, unless explicitly indicated otherwise or contradicted by context, the terms “a” and “an” are used interchangeably with “one or more” and “at least one”. In addition, these terms also specifically include the narrower meaning “one”, “exactly one” or “only one”. Accordingly, the articles “a” and “an” are used herein to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. By way of example, “an element” means one element or more than one element. As used herein, the term “and / or” refers to and encompasses any one of the corresponding items as well as any and all possible combinations of two or more of the corresponding items. Unless contradicted by context, this term also includes the specific meaning of “either … or”. Further, the terms “about” and “approximate”, as used herein, when referring to a measurable value such as an amount, dose, time, temperature, activity, level, number, frequency, percentage, dimension,size, amount, weight, position, length and the like, is meant to encompass variations of, e.g., ± 15%, ±10%, ± 5%, ± 1%, ± 0.5%, or even ± 0.1% of the specified amount, dose, time, temperature, activity, level, number, frequency, percentage, dimension, size, amount, weight, position, length and the like. In instances in which the terms “about” and “approximate” are used in connection with the location orposition of regions within a reference polypeptide, these terms encompass variations of, e.g., ± up to 20amino acid residues, ± up to 15 amino acid residues, ± up to 10 amino acid residues, ± up to 5 amino acid residues, ± up to 4 amino acid residues, ± up to 3 amino acid residues, ± up to 2 amino acid residues, or even ± 1 amino acid residue. Moreover, whenever the term “about” or “approximate” is used, the present invention also specifically and preferably relates to the corresponding exact value (without variation). It is to be understood that wherever numerical ranges are provided / disclosed herein, all values and subranges encompassed by the respective numerical range are meant to be encompassed within the scope of the invention. Accordingly, the present invention specifically and individually relates to each value (and particularly each integer) that falls within a numerical range disclosed herein, including the upper and lower endpoints of each numerical range, as well as each subrange encompassed by a numerical range disclosed herein. As used herein, the terms “optional”, “optionally” and “may” denote that the indicated feature may be present but can also be absent. Whenever the term “optional”, “optionally” or “may” is used, the present invention specifically relates to both possibilities, i.e., that the corresponding feature is present or, alternatively, that the corresponding feature is absent. For example, if a component of a composition is indicated to be “optional”, the invention specifically relates to both possibilities, i.e., that the corresponding component is present (contained in the composition) or that the corresponding component is absent from the composition. The term “adjuvant” as used herein refers to a compound that, when used in combination with a specific immunogen (e.g., a (poly)peptide, chimeric polypeptide, chimeric polypeptide complex, polynucleotide and nucleic acid construct of the present disclosure) in a composition, will augment the resultant immune response, including intensification and / or broadening the specificity of either or both antibody and cellular immune responses. In the context of the present disclosure, an adjuvant will preferably enhance the specific immunogenic effect of the active agents of the present disclosure. The term “adjuvant” is typically understood not to comprise agents which confer immunity by themselves. An adjuvant assists the immune system unspecifically to enhance the antigen-specific immune response by, e.g., promoting presentation of an antigen to the immune system or induction of an innate immune response. As used herein, the term “antigen” and its grammatically equivalent expressions (e.g., “antigenic”) refer to a compound, composition, or substance that may be specifically bound by the products of specific humoral or cellular immunity, such as an antibody molecule or T-cell receptor. Antigens can be any type of molecule including, for example, haptens, simple intermediary metabolites, sugars (e.g., oligosaccharides), lipids, and hormones as well as macromolecules such as complex carbohydrates (e.g., polysaccharides), phospholipids, and proteins. Common categories of antigens include, but are not limited to, viral antigens, bacterial antigens, fungal antigens, protozoan and other parasitic antigens, tumor antigens, antigens involved in autoimmune disease, allergy and graft rejection, toxins, and other miscellaneous antigens. As mentioned herein above, the present invention particularly relates to antigens (i.e., chimeric polypeptides) comprising RSV fusion proteins (or fragments thereof). By “antigen-binding molecule” is meant a molecule that has binding affinity for a target antigen. It will be understood that this term extends to immunoglobulins, immunoglobulin fragments and non- immunoglobulin derived protein or other non-protein frameworks that exhibit antigen-binding activity. Representative antigen-binding molecules that are useful in the practice of the present disclosure include polyclonal and monoclonal antibodies as well as their fragments (such as Fab, Fab’, F(ab’)2, or Fv), single chain (scFv) and single domain antibodies (including, for example, shark and camelid antibodies), and fusion proteins comprising an antibody, and any other modified configuration of the immunoglobulin molecule that comprises an antigen binding / recognition site. An antibody includes an antibody of any class, such as IgG, IgA, or IgM (or sub-class thereof), and the antibody need not be of any particular class. Depending on the antibody amino acid sequence of the constant region of its heavy chains, immunoglobulins can be assigned to different classes. There are five major classes of immunoglobulins: IgA, IgD, IgE, IgG, and IgM, and several of these may be further divided into subclasses (isotypes), e.g., IgG1, IgG2, IgG3, IgG4, IgA1 and IgA2. The heavy-chain constant regions that correspond to the different classes of immunoglobulins are called α, δ, ε, γ, and µ, respectively. The subunit structures and three-dimensional configurations of different classes of immunoglobulins are well known. Antigen-binding molecules also encompass dimeric antibodies, as well as multivalent forms of antibodies. In some embodiments, the antigen-binding molecules are chimeric antibodies in which a portion of the heavy and / or light chain is identical with or homologous to corresponding sequences in antibodies derived from a particular species or belonging to a particular antibody class or subclass, while the remainder of the chain(s) is identical with or homologous to corresponding sequences in antibodies derived from another species or belonging to another antibody class or subclass, as well as fragments of such antibodies, so long as they exhibit the desired biological activity. Also contemplated are humanized antibodies, which are generally produced by transferring complementarity determining regions (CDRs) from heavy and light variable chains of a non-human (e.g., rodent, preferably mouse) immunoglobulin into a human variable domain. Typical residues of human antibodies are then substituted in the framework regions of the non-human counterparts. The use of antibody components derived from humanized antibodies obviates potential problems associated with the immunogenicity of non-human constant regions. General techniques of cloning non-human, particularly murine, immunoglobulin variable domains as well as techniques for producing humanized monoclonal antibodies are well-known in the art and described in the literature. Humanized antibodies include “primatized” antibodies in which the antigen-binding region of the antibody is derived from an antibody produced by immunizing macaque monkeys with the antigen of interest. Also contemplated as antigen-binding molecules are humanized antibodies. Further examples of an “antigen-binding molecule” include any of the above-described agents, which can be obtained, e.g., by using the method according to the ninth aspect of theinvention. The term “anti-parallel”, as used herein, refers to a proteinaceous polymer in which regions or segments of the polymer are in a parallel orientation but have opposite polarities. As used herein, the term “binds specifically” refers to a binding reaction which is determinative of the presence of a chimeric polypeptide or complex of the present disclosure in the presence of a heterogeneous population of molecules including macromolecules such as proteins and other biologics. In specific embodiments, the term “binds specifically” when referring to an antigen-binding molecule is used interchangeably with the term “specifically immuno-interactive” and the like to refer to a binding reaction which is determinative of the presence of a chimeric polypeptide or complex of the present disclosure in the presence of a heterogeneous population of proteins and other biologics. Under designated assay conditions, a molecule binds specifically to a chimeric polypeptide or complex of the disclosure and does not bind in a significant amount to other molecules (e.g., proteins or antigens) present in the sample. In antigen-binding molecule embodiments, a variety of immunoassay formats may be used to select antigen-binding molecules that are specifically immuno-interactive with a chimeric polypeptide or complex of the disclosure. For example, solid-phase ELISA immunoassays are routinely used to select monoclonal antibodies that are specifically immuno-interactive with a protein. The term “chimeric”, when used in reference to a molecule, means that the molecule contains portions that are derived from, obtained or isolated from, or based upon two or more different origins or sources. Thus, a polypeptide is chimeric when it comprises two or more amino acid sequences of different origin and includes (1) polypeptide sequences that are not found together in nature (i.e., at least one of the amino acid sequences is heterologous with respect to at least one of its other amino acid sequences), or (2) amino acid sequences that are not naturally adjoined. It is understood that a “chimeric polypeptide” is a “polypeptide”. Accordingly, in the context of the present invention a “chimeric polypeptide” may also be referred to as a “polypeptide”. By “coding sequence” is meant any nucleic acid sequence that contributes to the code for the polypeptide product of a gene or for the final mRNA product of a gene (e.g., the mRNA product of a gene following splicing). By contrast, the term “non-coding sequence” refers to any nucleic acid sequence that does not contribute to the code for the polypeptide product of a gene or for the final mRNA product of a gene. The term “a nucleic acid encoding a polypeptide” may be used interchangeably with the term “a nucleic acid comprising a coding sequence encoding a polypeptide” or the like. The terms “coiled coil” or “coiled coil structure” are used interchangeably herein to refer to a structural motif in proteins, in which two or more α-helices (most often 2-7 α-helices) are coiled together like the strands of a rope (dimers and trimers are the most common types). Many coiled coil type proteins are involved in important biological functions such as the regulation of gene expression, e.g., transcription factors. Coiled coils often, but not always, contain a repeated pattern, hpphppp or hppphpp, of hydrophobic (h) and polar (p) amino-acid residues, referred to as a heptad repeat (as further explained herein below). This repeating pattern in a (poly)peptide sequence naturally folds into an α-helical secondary structure resulting in the presentation of the hydrophobic residues along one face of the helix and the hydrophilic residues along the opposite face forming an amphipathic structure. The most favorable way for two or three such helices to arrange themselves in a water-filled environment is to wrap or sequester the hydrophobic faces of the helix against each other leaving the hydrophilic amino acids solvent exposed. It is thus the burial of hydrophobic surfaces, which provides the thermodynamic driving force for oligomerization of the α-helices and the stability of the structure. The packing in a coiled-coil interface is exceptionally tight. The α-helices may be parallel or anti-parallel, and usually adopt a left-handed super-coil. Although disfavored, a few right-handed coiled coils have also been observed in nature and in designed proteins. The term “coiled coil” or “coiled coil structure” is well- known in the art. Particular reference in this regard is made to review papers concerning coiled-coil structures, such as for example, Cohen and Parry (Proteins 1990, 7:1-15); Kohn and Hodges (TrendsBiotechnol 1998, 16:379-389); Schneider et al. (Fold Des 1998, 3:R29-R40); Harbury et al. (Science 1998,282:1462-1467); Mason and Arndt (Chem-BioChem 2004, 5:170-176); Lupas and Gruber (Adv ProteinChem 2005, 70:37-78); Woolfson (Adv Protein Chem 2005, 70:79-112); Parry et al. (J Struct Biol 2008,163:258-269); and Mcfarlane et al. (Eur J Pharmacol 2009, 625:101-107).The term “heptad repeat region” (as used, e.g., in the expressions “first heptad repeat region” (FHRR) and “second heptad repeat region” (SHRR)), are well-known in the art and are further explained in WO 2023 / 187743 which is incorporated herein by reference in its entirety. A heptad repeat region is a structural motif that forms the basis of most coiled coils. Alpha-helical coiled coils have been characterized at the level of their amino acid sequences in that each helix is constituted of a series of heptad repeats. A heptad repeat (heptad unit, heptad) is a 7-residue sequence motif which can be encoded as hpphppp, wherein each “h” is a hydrophobic amino acid residue and each “p” is apolar (i.e., hydrophilic) amino acid residue. Occasionally, p-residues are observed at h-positions, and viceversa. A heptad repeat is also often encoded by the patterns a-b-c-d-e-f-g (abcdefg) or d-e-f -g-a-b-c (defgabc), in which case the indices “a” to “g” refer to the conventional heptad positions at which typical amino acid types are observed. By convention, the indices “a” and “d” denote the positions of the core residues (central, buried residues) in a coiled coil. The typical amino acid types that are observed at core a- and d-positions are hydrophobic amino acid residues; at all other positions (non-core positions), predominantly polar (hydrophilic) residues are observed. Thus, conventional heptad patterns “hpphppp” match with the pattern notation “abcdefg” (while “hppphpp” patterns match with the pattern notation “defgabc”, this notation being used for coiled coils starting with a hydrophobic residue at a d- position). The heptad repeat regions (HRRs) as referred to herein include at least 2, and suitably 3 or more(preferably consecutive, i.e. uninterrupted) heptad repeats in individual α-helices of the coiled coilstructure. Each series of consecutive heptad repeats in a helix is denoted a “heptad repeat sequence” (HRS). The start and end of a heptad repeat sequence is preferably determined on the basis of the experimentally determined three-dimensional (3D) structure, if available. If a 3D structure is not available, the start and end of a heptad repeat sequence is preferably determined on the basis of an optimal overlay of a (hpphppp)n or (hppphpp)n pattern with the actual amino acid sequence, where “h” and “p” denote hydrophobic and polar (hydrophilic) residues, respectively, and where “n” is a number equal to or greater than 2. The start and end of each heptad repeat sequence is taken to be the first and last hydrophobic residue at an a- or d-position, respectively. Conventional h-residues are preferably selected from valine, isoleucine, leucine, methionine, phenylalanine, tyrosine, tryptophan, histidine, glutamine, threonine, serine and alanine, more preferably from valine, isoleucine, leucine and methionine, and even more preferably isoleucine. Conventional p-residues are preferably selected from glycine, alanine, cysteine, serine, threonine, histidine, asparagine, aspartic acid, glutamine, glutamic acid, lysine and arginine. In case this method does not permit unambiguous assignment of amino acid residues to a heptad repeat sequence, a more specialized analysis method can be applied, such as, e.g.,the COILS method of Lupas et al. (Science 1991, 252(5009): 1162-1164; DOI:10.1126 / science.252.5009.1162; see also: https: / / bio.tools / coils). As used herein the term “complementary” and grammatically equivalent expressions thereof refer to the characteristic of two or more structural elements (e.g., peptide, polypeptide, nucleic acid, small molecule, or portions thereof etc.) of being able to hybridize, oligomerize (e.g., dimerize), interact or otherwise form a complex with each other. For example, “complementary regions of a polypeptide” are capable of coming together to form a complex. As used herein, the term “complex” refers to an assemblage or aggregate of molecules (e.g., peptides, polypeptides, etc.) in direct and / or indirect contact with one another. In specific embodiments, “contact”, or more particularly, “direct contact” means that two or more molecules are close enough so that attractive noncovalent interactions, such as Van der Waal forces, hydrogen bonding, ionic and hydrophobic interactions, and the like, dominate the interaction of the molecules. In such embodiments, a complex of molecules (e.g., a peptide and polypeptide) is formed under conditions such that the complex is thermodynamically favored (e.g., compared to a non-aggregated, or non-complexed, state of its component molecules). As used herein the term “complex”, unless described otherwise, refers to the assemblage of two or more molecules (e.g., peptides, polypeptides or a combination thereof). Herein, the term “complex” may specifically refer to the assemblage of three polypeptides. Throughout this specification, unless the context requires otherwise, the words “comprise,” “comprises” and “comprising”, as well as “contain”, “contains” and “containing”, will be understood to imply the inclusion of a stated step or element or group of steps or elements but not the exclusion of any other step or element or group of steps or elements. Thus, use of the term “comprising” and the like indicates that the listed elements are required or mandatory, but that other elements are optional and may or may not be present. By “consisting of” is meant including, and limited to, whatever follows the phrase “consisting of”. Thus, the phrase “consisting of” indicates that the listed elements are required or mandatory, and that no other elements may be present. Throughout the present specification, the term “comprising” (or “containing” or the like) also includes the narrower meanings of “consisting essentially of” and “consisting of”. Accordingly, whenever the term “comprising” (or “containing”, “having” or the like) is used, the invention also specifically relates to the corresponding subject-matter defined by the term “consisting essentially of” as well as the corresponding subject-matter defined by the term “consisting of” (in place of “comprising” or “containing”). As used herein, the terms “conjugated”, “linked”, “fused” or “fusion” and their grammatical equivalents, in the context of joining together of two or more elements or components or domains by whatever means including chemical conjugation or recombinant means (e.g., by genetic fusion) are used interchangeably. Methods of chemical conjugation (e.g., using heterobifunctional crosslinking agents) are known in the art. More specifically, as used herein, a “(poly)peptide” – “structure-stabilizing moiety” fusion or conjugate refers to the genetic or chemical conjugation of the (poly)peptide, which is suitably in a metastable, pre-fusion conformation, to a structure-stabilizing moiety. A “conservative amino acid substitution” is one in which the amino acid residue is replaced with an amino acid residue having a similar side chain. Families of amino acid residues having similar side chains have been defined in the art, which can be generally sub-classified in the context of amino acid substitutionsas shown in Table 1: Table 1 Amino acid sub-classification Sub-classes Amino acidsAcidic Aspartic acid, Glutamic acidBasic Noncyclic: Arginine, Lysine; Cyclic: HistidineCharged Aspartic acid, Glutamic acid, Arginine, Lysine, HistidineSmall Glycine, Serine, Alanine, Threonine, ProlineHydrophilic (polar) / neutral Asparagine, Histidine, Glutamine, Cysteine, Serine, Threonine Hydrophilic (polar) / large Asparagine, GlutamineHydrophobic (non-polar) Tyrosine, Valine, Isoleucine, Leucine, Methionine, Phenylalanine,Tryptophan Aromatic Tryptophan, Tyrosine, PhenylalanineResidues that influence Glycine and Proline chain orientation Conservative amino acid substitution also includes groupings based on side chains. For example, a group of amino acids having aliphatic side chains is glycine, alanine, valine, leucine, and isoleucine; a group of amino acids having aliphatic-hydroxyl side chains is serine and threonine; a group of amino acids having amide-containing side chains is asparagine and glutamine; a group of amino acids having aromatic side chains is phenylalanine, tyrosine, and tryptophan; a group of amino acids having basic side chains is lysine, arginine, and histidine; and a group of amino acids having sulfur-containing side chains is cysteine and methionine. For example, it is reasonable to expect that replacement of a leucine with an isoleucine or valine, an aspartate with a glutamate, a threonine with a serine, or a similar replacement of an amino acid with a structurally related amino acid will not have a major effect on the properties of the resulting variant polypeptide. Whether an amino acid change results in a functional polypeptide can readily bedetermined by assaying its activity. Conservative substitutions are shown in Table 2 under the headingof exemplary and preferred substitutions. Amino acid substitutions falling within the scope of the disclosure, are, in general, accomplished by selecting substitutions that do not differ significantly in their effect on maintaining (a) the structure of the peptide backbone in the area of the substitution, (b) the charge or hydrophobicity of the molecule at the target site, or (c) the bulk of the side chain. After the substitutions are introduced, the variants are screened for biological activity. Table 2 Exemplary and Preferred Amino Acid Substitutions Original Residue Exemplary Substitutions Preferred SubstitutionsAla Val, Leu, Ile ValArg Lys, Gln, Asn LysAsn Gln, His, Lys, Arg GlnAsp Glu GluCys Ser SerGln Asn, His, Lys, AsnGlu Asp, Lys AspGly Pro ProHis Asn, Gln, Lys, Arg ArgIle Leu, Val, Met, Ala, Phe, Norleu LeuLeu Norleu, Ile, Val, Met, Ala, Phe IleLys Arg, Gln, Asn ArgMet Leu, Ile, Phe LeuPhe Leu, Val, Ile, Ala LeuPro Gly GlySer Thr ThrThr Ser SerTrp Tyr TyrTyr Trp, Phe, Thr, Ser PheVal Ile, Leu, Met, Phe, Ala, Norleu LeuThe herein provided nucleic acids encoding chimeric polypeptides may be constructs for example comprising a nucleic acid sequence encoding an RSV fusion protein and a structure-stabilizing moiety. The term “construct” refers to a recombinant genetic molecule including one or more isolated nucleic acid sequences from different sources. Thus, constructs are chimeric molecules in which two or more nucleic acid sequences of different origin are assembled into a single nucleic acid molecule and include any construct that contains (1) nucleic acid sequences, including regulatory and coding sequences that are not found together in nature (i.e., at least one of the nucleotide sequences is heterologous with respect to at least one of its other nucleotide sequences), or (2) sequences encoding parts of functional RNA molecules or proteins not naturally adjoined, or (3) parts of promoters that are not naturally adjoined. Representative constructs include any recombinant nucleic acid molecule such as a plasmid, cosmid, virus, autonomously replicating polynucleotide molecule, phage, or linear or circular single stranded or double stranded DNA or RNA nucleic acid molecule, derived from any source, capable of genomic integration or autonomous replication, comprising a nucleic acid molecule where one or more nucleic acid molecules have been operably linked. Constructs of the present disclosure will generally include the necessary elements to direct expression of a nucleic acid sequence of interest that is also contained in the construct, such as, for example, a target nucleic acid sequence or a modulator nucleic acid sequence. Such elements may include control elements such as a promoter that is operably linked to (so as to direct transcription of) the nucleic acid sequence of interest, and often includes a polyadenylation sequence as well. Within certain embodiments of the disclosure, the construct may be contained within a vector. In addition to the components of the construct, the vector may include, for example, one or more selectable markers, one or more origins of replication, such as prokaryotic and eukaryotic origins, at least one multiple cloning site, and / or elements to facilitate stable integration of the construct into the genome of a host cell. Two or more constructs can be contained within a single nucleic acid molecule, such as a single vector, or can be containing within two or more separate nucleic acid molecules, such as two or more separate vectors. An “expression construct” generally includes at least a control sequence operably linked to a nucleotide sequence of interest. In this manner, for example, promoters in operable connection with the nucleotide sequences to be expressed are provided in expression constructs for expression in an organism or part thereof including a host cell. For the practice of the present disclosure, conventional compositions and methods for preparing and using constructs and host cells are well known to one skilled in the art, see for example, Molecular Cloning: A Laboratory Manual, 3rdedition Volumes 1, 2, and 3. J. F. Sambrook, D. W. Russell, and N. Irwin, Cold Spring Harbor Laboratory Press, 2000. By “effective amount”, in the context of treating, inhibiting the development of, or preventing a condition is meant the administration of an amount of an agent or composition to an individual in need of such treatment, inhibition or prophylaxis, either in a single dose or as part of a series, that is effective for the prevention of incurring a symptom, holding in check such symptoms, and / or treating existing symptoms, of that condition. The effective amount will vary depending upon the health and physical condition of the individual to be treated, the taxonomic group of the individual to be treated, the formulation of the composition, the assessment of the medical situation, and other relevant factors. It is expected that the amount will fall in a relatively broad range that can be determined through routine trials. By the term “linker”, or “flexible linker”, it is meant a molecule or group of molecules (such as a monomer or polymer) that connects two molecules and often serves to place the two molecules in a desirable configuration. The terms “linker”, and “flexible linker”, may herein be used synonymously. The term “linker” or “flexible linker” as used herein preferably refers to a proteinaceous molecule containing at least one amino acid residue, usually at least two amino acids residues joined by peptide bond(s), which molecule permits two polypeptides linked thereby to move more freely relative to one another, as compared to their movement without the flexible linker. In certain embodiments, the flexible linker provides increased rotational freedom for two polypeptides linked thereby than the two linked polypeptides would have in the absence of the flexible linker. Such freedom of relative movement or rotational freedom allows polypeptides joined by the flexible linker to perform their individual functions or elicit their activities with less structural hindrance. A flexible linker may be characterized by the absence of secondary structures such as helices or β-sheets or a maximal secondary structure content of 10%, 20% 30% or 40%. Non-limiting examples of flexible linkers include the amino acid GGSGG (SEQ ID NO: 32), GSG, GS, GGSG (SEQ ID NO: 33), GSGS (SEQ ID NO: 34), AS, GGGS (SEQ ID NO: 35), G4S (SEQ ID NO: 36), (G4S)2 (SEQ ID NO: 37), (G4S)3 (SEQ ID NO: 38), (G4S)4 (SEQ ID NO: 39), G4SG (SEQ ID NO: 40), GSGG (SEQ ID NO: 41) and GSGGS (SEQ ID NO: 42). Additional flexible linker sequences are well known in the art. In various embodiments, the flexible linker contains or consists of at least 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or 100 amino acid residues. In some of the same and other embodiments, the flexible linker contains or consists of up to 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or 100 amino acid residues. In some of the same and other embodiments, the flexible linker contains or consists of between about 1 to about 30 amino acid residues, between about 1 to about 25 amino acid residues, between about 1 to about 20 amino acid residues, between about 1 to about 15 amino acid residues, between about 1 to about 12 amino acid residues, between about 1 to about 10 amino acid residues, between about 1 to about 8 amino acid residues, between about 1 to about 6 amino acid residues, between about 1 to about 5 amino acid residues, between about 1 to about 4 amino acid residues, or between about 1 to about 3 amino acid residues. In some of the same and other embodiments, the flexible linker contains or consists of between about 2 to about 30 amino acid residues, between about 2 to about 25 amino acid residues, between about 2 to about 20 amino acid residues, between about 2 to about 15 amino acid residues, between about 2 to about 12 amino acid residues, between about 2 to about 10 amino acid residues, between about 2 to about 8 amino acid residues, between about 2 to about 6 amino acid residues, between about 2 to about 5 amino acid residues, or between about 2 to about 4 amino acid residues. In some of the same and other embodiments, the flexible linker contains or consists of between about 3 to about 30 amino acid residues, between about 3 to about 25 amino acid residues, between about 3 to about 20 amino acid residues, between about 3 to about 15 amino acid residues, between about 3 to about 12 amino acid residues, between about 3 to about 10 amino acid residues, between about 3 to about 8 amino acid residues, between about 3 to about 6 amino acid residues, or between about 3 to about 5 amino acid residues. In certain embodiments, the flexible linker contains or consists of 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 amino acid residues. In particular, a flexible linker may be composed of amino acid residues (e.g., having any of the above-mentioned exemplary numbers of amino acid residues), wherein preferably at least about 70% (more preferably at least about 80%, even more preferably at least about 90%, even more preferably at least about 95%, still more preferably 100%) of said amino acid residues are selected from glycine, serine and alanine; more preferably, at least about 70% (more preferably at least about 80%, even more preferably at least about 90%, even more preferably at least about 95%, still more preferably 100%) of said amino acid residues are selected from glycine and serine. In some embodiments, the said amino acid residues are all glycine. As used herein, the term “moiety” refers to a portion of a molecule, which may be a functional group, a set of functional groups, and / or a specific group of atoms within a molecule, that is responsible for a characteristic chemical, biological, and / or medicinal property of the molecule. The term “oligomer” refers to a molecule that consists of more than one but a limited number of monomer units in contrast to a polymer that, at least in principle, consists of an unlimited number of monomers. Oligomers include, but are not limited to, dimers, trimers, tetramers, pentamers, hexamers, heptamers, octamers, nonamers, decamers and the like. An oligomer can be a macromolecular complex formed by non-covalent bonding of macromolecules like proteins. In this sense, a homo-oligomer would be formed by identical molecules and by contrast, a hetero-oligomer would be made of at least two different molecules., or a “heterotrimeric polypeptide complex” consisting of three polypeptide subunits in which at least one subunit polypeptide is non-identical. In the context of the herein provided chimeric polypeptides, it is preferred that the RSV fusion protein and the structure-stabilizing moiety are operably linked (optionally by a linker). The term “operably connected” or “operably linked” as used herein refers to a juxtaposition wherein the components so described are in a relationship permitting them to function in their intended manner. For example, a regulatory sequence (e.g., a promoter) “operably linked” to a nucleotide sequence of interest (e.g., a coding and / or non-coding sequence) refers to positioning and / or orientation of the regulatory sequence relative to the nucleotide sequence of interest to permit expression of that sequence under conditions compatible with the regulatory sequence. The regulatory sequences need not be contiguous with the nucleotide sequence of interest, so long as they function to direct its expression. Thus, for example, intervening non-coding sequences (e.g., untranslated, yet transcribed, sequences) can be present between a promoter and a coding sequence, and the promoter sequence can still be considered “operably linked” to the coding sequence. Likewise, “operably connecting” an RSV fusion protein to a structure-stabilizing moiety (SSM) encompasses positioning and / or orientation of the structure-stabilizing moiety (SSM) such that it can, under suitable conditions (e.g., in aqueous solution and / or physiological conditions), associate with the structure-stabilizing moieties (SSMs) of two further chimeric polypeptides to form a trimer, wherein preferably, in the trimer, the FHRRs and SHRRs of the three SSMs are associated in the form of a six-helix bundle. The terms “patient”, “subject”, “host” or “individual” used interchangeably herein, refer to any subject, particularly a vertebrate subject, and even more particularly a mammalian subject, for whom therapy or prophylaxis is desired. Suitable vertebrate animals that fall within the scope of the disclosure include, but are not restricted to, any member of the subphylum Chordata including primates (e.g., humans,monkeys and apes, and includes species of monkeys such from the genus Macaca (e.g., cynomolgusmonkeys such as Macaca fascicularis, and / or rhesus monkeys (Macaca mulatta)) and baboon (Papioursinus), as well as marmosets (species from the genus Callithrix), squirrel monkeys (species from thegenus Saimiri) and tamarins (species from the genus Saguinus), as well as species of apes such aschimpanzees (Pan troglodytes)), rodents (e.g., mice, rats, guinea pigs), lagomorphs (e.g., rabbits, hares), bovines (e.g., cattle), ovines (e.g., sheep), caprines (e.g., goats), porcines (e.g., pigs), equines (e.g., horses), canines (e.g., dogs), felines (e.g., cats), avians (e.g., chickens, turkeys, ducks, geese, or otherpoultry, companion birds such as canaries, budgerigars etc.), marine mammals (e.g., dolphins, whales),reptiles (snakes, frogs, lizards etc.), and fish. Further, cotton rats and ferrets are herein considered asparticularly suitable hosts. A preferred subject is a human, particularly a human in need of eliciting an immune response to a fusion protein of an enveloped virus (such as RSV), or complex thereof. However, it will be understood that the aforementioned terms do not imply that symptoms are present. By “pharmaceutically acceptable carrier” is meant a solid or liquid filler, diluent or encapsulating substance that can be safely used in topical or systemic administration to an animal, preferably a mammal, including humans. Representative pharmaceutically acceptable carriers include any and all solvents, dispersion media, coatings, surfactants, antioxidants, preservatives (e.g., antibacterial agents, antifungal agents), isotonic agents, absorption delaying agents, salts, preservatives, drugs, drug stabilizers, gels, binders, excipients, disintegration agents, lubricants, sweetening agents, flavoring agents, dyes, such like materials and combinations thereof. Except insofar as any conventional carrier is incompatible with the active ingredient(s), its use in the pharmaceutical compositions is contemplated. The terms “peptide”, “polypeptide”, “(poly)peptide” and “protein” are used herein interchangeably and refer to a polymer of two or more amino acids linked via amide bonds (i.e., peptide bonds) that are formed between an amino group of one amino acid and a carboxyl group of another amino acid. The amino acids comprised in the peptide, polypeptide, (poly)peptide, or protein, which are also referred to as amino acid residues, may be selected from the 20 standard proteinogenic α-amino acids (i.e., Ala, Arg, Asn, Asp, Cys, Glu, Gln, Gly, His, Ile, Leu, Lys, Met, Phe, Pro, Ser, Thr, Trp, Tyr, and Val) but also from non- proteinogenic and / or non-standard α-amino acids (such as, e.g., ornithine, citrulline, homolysine, pyrrolysine, 4-hydroxyproline, α-methylalanine (i.e., 2-aminoisobutyric acid), norvaline, norleucine, terleucine (tert-leucine), labionin, or an alanine or glycine that is substituted at the side chain with a cyclic group such as, e.g., cyclopentylalanine, cyclohexylalanine, phenylalanine, naphthylalanine, pyridylalanine, thienylalanine, cyclohexylglycine, or phenylglycine) as well as β-amino acids (e.g., β- alanine), γ-amino acids (e.g., γ-aminobutyric acid, isoglutamine, or statine) and δ-amino acids. Preferably, the amino acid residues comprised in the peptide, polypeptide or protein are selected from α-amino acids, more preferably from the 20 standard proteinogenic α-amino acids (which can be present as the L-isomer or the D-isomer, and are preferably all present as the L-isomer). The peptide, polypeptideor protein may be unmodified or may be modified, e.g., at its N-terminus, at its C-terminus and / or at afunctional group in the side chain of any of its amino acid residues (particularly at the side chain functional group of one or more Lys, His, Ser, Thr, Tyr, Cys, Asp, Glu, and / or Arg residues). Such modifications may include, e.g., the attachment of any of the protecting groups described for the corresponding functional groups in: Wuts PG & Greene TW, Greene’s protective groups in organic synthesis, John Wiley & Sons, 2006. Such modifications may also include the covalent attachment of one or more polyethylene glycol (PEG) chains (forming a PEGylated peptide, polypeptide or protein), the covalent attachment of albumin, the glycosylation and / or the acylation with one or more fatty acids (e.g., one or more C8-30 alkanoic or alkenoic acids; forming a fatty acid acylated peptide, polypeptide or protein). Moreover, such modified peptides, polypeptide or proteins may also include peptidomimetics, provided that they contain at least two amino acids that are linked via an amide bond (formed between an amino group of one amino acid and a carboxyl group of another amino acid). The amino acid residuescomprised in the peptide, polypeptide or protein may, e.g., be present as a linear molecular chain(forming a linear peptide, polypeptide or protein) or may form one or more rings (corresponding to a cyclic peptide, polypeptide or protein). The peptide, polypeptide or protein may also form oligomers consisting of two or more identical or different molecules. Accordingly, peptides, polypeptides and proteins may form dimers, trimers and higher oligomers, wherein the peptide, polypeptide or protein molecules forming such dimers, trimers etc. may be identical or non-identical. The corresponding higher order structures are, consequently, termed homo- or heterodimers, homo- or heterotrimers, and homo- or heterooligomers (etc.). Such dimers, trimers and oligomers are likewise embraced by the terms “peptide”, “polypeptide”, “(poly)peptide” and “protein”. The term “amino acid” refers, in particular, to any one of the 20 standard proteinogenic α-amino acids (i.e., Ala, Arg, Asn, Asp, Cys, Glu, Gln, Gly, His, Ile, Leu, Lys, Met, Phe, Pro, Ser, Thr, Trp, Tyr, and Val) but also to non-proteinogenic and / or non-standard α-amino acids (such as, e.g., ornithine, citrulline, homolysine, pyrrolysine, 4-hydroxyproline, α-methylalanine (i.e., 2-aminoisobutyric acid), norvaline, norleucine, terleucine (tert-leucine), labionin, or an alanine or glycine that is substituted at the side chain with a cyclic group such as, e.g., cyclopentylalanine, cyclohexylalanine, phenylalanine, naphthylalanine, pyridylalanine, thienylalanine, cyclohexylglycine, or phenylglycine) as well as β-amino acids (e.g., β- alanine), γ-amino acids (e.g., γ-aminobutyric acid, isoglutamine, or statine) and / or δ-amino acids as well as any other compound comprising at least one carboxylic acid group and at least one amino group. Unless defined otherwise, an “amino acid” preferably refers to an α-amino acid, more preferably to any one of the 20 standard proteinogenic α-amino acids (which can be present as the L-isomer or the D- isomer, and are preferably present as the L-isomer). Whenever an amino acid is referred to herein, unless explicitly stated otherwise, it is preferred that the corresponding amino acid is an L-amino acid. Likewise, whenever an amino acid sequence is referred to herein, unless explicitly stated otherwise, it is preferred that all amino acids in the corresponding amino acid sequence are L-amino acids. As used herein, the term “post-fusion conformation” of a viral fusion protein refers to the structure of the virus fusion protein which is in a terminal conformation (i.e., formed at the end of the fusion process) and is the most energetically favorable state. In the post-fusion conformation, the fusion peptides or loops of the fusion protein are brought into close proximity with the fusion protein transmembrane domain. The specific structural elements that facilitate formation of the hairpin structure vary according to the class of enveloped fusion protein. For example, the post-fusion conformation of a Class I fusion protein is characterized by interaction between the endogenous FHRR region and the endogenous SHRR region of individual Class I fusion proteins to form a hairpin structure characterized by a six-helix bundle, comprising three endogenous SHRR and three endogenous FHRR regions. Alternatively, the post-fusion conformation of a Class III fusion protein is characterized by interaction between the internal fusion loops and the C-terminal transmembrane region which facilitates the formation of a hairpin structure. Post-fusion conformations of individual viral fusion proteins have been determined by electron microscopy and / or X-ray crystallography, such structures are readily identifiable when viewed in negatively stained electron micrographs and / or by a lack of pre-fusion epitopes. As used herein, the term “pre-fusion conformation”, “pre-fusion state” or the like of a viral fusion protein refers to the structure of the viral fusion protein which is in a meta-stable confirmation (i.e., in a semi- stable conformation that is not the most energetically favorable terminal conformation) and upon appropriate triggering is able to undergo conformational rearrangement to the terminal post-fusion conformation. Typically, pre-fusion conformations of viral fusion proteins contain a hydrophobic sequence, referred to as the fusion peptide or fusion loop, that is located internally within the pre-fusion conformation and cannot interact with either the viral or host cell membranes. Upon triggering this hydrophobic sequence is inserted into the host cell membrane and the fusion protein collapses into the post-fusion hairpin like conformation. The pre-fusion conformation of viral fusion proteins varies according to the class of enveloped fusion protein. Each class is characterized by non-interacting structural elements that subsequently associate in the energetically favorable post-fusion conformation. For example, the pre-fusion conformation of a Class I fusion protein is dependent on the endogenous FHRR region not interacting with the endogenous SHRR region of individual fusion proteins of the trimer, thereby not permitting formation of a hairpin structure characterized by a six-helix bundle. Alternatively, the pre-fusion conformation of a Class III fusion protein is dependent a central a-helical coiled coil not interacting with fusion loop(s) at the C-terminal region of individual fusion proteins of the trimer, thereby not permitting formation of a hairpin structure. Pre-fusion conformations of individual viral fusion proteins have been determined by electron microscopy and / or X-ray crystallography, such structures are readily identifiable when viewed in negatively stained electron micrographs and / or by pre-fusion epitopes that are not present on post-fusion conformations. The term “sequence identity”, as used herein, refers to the sequence match between two (poly)peptides or nucleic acids. The (poly)peptide or nucleic acid sequences to be compared are aligned to give maximum identity, for example, using bioinformatics tools for pairwise alignment such as EMBOSSNeedle (https: / / www.ebi.ac.uk / Tools / psa / emboss_needle / ; see also Madeira F, et al. The EMBL-EBIsearch and sequence analysis tools APIs in 2019. Nucleic Acids Research.2019 Jul;47(W1):W636-W641. DOI: 10.1093 / nar / gkz268). When the same position in the sequences to be compared is occupied by the same nucleobase or amino acid residue, then the respective molecules are identical at that very position. Accordingly, the “sequence identity”, “percent identity” or “percent sequence identity” is a function of the number of matching positions divided by the number of positions compared and multiplied by 100%. For example, if 6 out of 10 sequence positions are identical, then the identity is 60%. The “identity” or“percent (%) identity” between two amino acid sequences can, e.g., be determined by using theNeedleman-Wunsch algorithm (Needleman, S.B. and Wunsch, CD. A general method applicable to thesearch for similarities in the amino acid sequence of two proteins. J Mol Biol. 1970;48(3):443-53. DOI:10.1016 / 0022-2836(70)90057-4.) which has been incorporated into EMBOSS Needle, using a BLOSUM62 matrix, a "gap open penalty" of 10, a "gap extend penalty" of 0.5, a false "end gap penalty", an "end gap open penalty" of 10 and an "end gap extend penalty" of 0.5. The percent (%) identity is typically determined over the entire length of the query sequence on which the analysis is performed. Two molecules having the same primary amino acid or nucleic acid sequence are identical irrespective of any chemical and / or biological modification. For example, two antibodies having the same primary amino acid sequence, but different glycosylation patterns are identical by this definition. In case of nucleic acids, for example, two molecules having the same sequence but different linkage components such as thiophosphate instead of phosphate are identical by this definition. Accordingly, the skilled person can readily determine the ‘corresponding positions’ in a reference amino acid sequence. For example, a position 'corresponding to' a specific position in a reference sequence (e.g., SEQ ID NO: 26) can be determined by aligning a variant sequence with the reference sequence using a standard algorithm, such as the Needleman-Wunsch algorithm with default parameters as implemented in EMBOSS Needle, and identifying the residue in the variant sequence that aligns with the specified residue in the reference sequence. As used herein, the terms “treatment”, “treating”, and the like, refer to obtaining a desired pharmacologic and / or physiologic effect. The effect may be prophylactic in terms of completely or partially preventing a disease or symptom thereof and / or may be therapeutic in terms of a partial or complete cure for a disease and / or adverse effect attributable to the disease. “Treatment”, as used herein, covers any treatment of a disease in a mammal, particularly in a human, and includes: (a) preventing the disease from occurring in a subject which may be predisposed to the disease but has notyet been diagnosed as having it; (b) inhibiting the disease, i.e., arresting its development; and (c) relievingthe disease, i.e., causing regression of the disease.The terms “wild-type”, “native” and “naturally occurring” are used interchangeably herein to refer to a gene or gene product that has the characteristics of that gene or gene product when isolated from a naturally occurring source. A wild type, native or naturally occurring gene or gene product (e.g., a polypeptide) is that which is most frequently observed in a population and is thus arbitrarily designed the “normal” or “wild-type” form of the gene or gene product. The term “S508”, “RSV F SC9-10AY-508-CT5S”, “SC9-10AY-508”, or the like may herein be used synonymously. The term “adverse event” or “AE”, as used herein, refers to any untoward medical occurrence in a clinical trial participant administered an investigational medicinal product (IMP) or a control (such as a placebo or a comparator drug), which does not necessarily have a causal relationship with the treatment. An AE can therefore be any unfavorable and unintended sign, including an abnormal laboratory or instrumental finding, symptom, or disease that is temporally associated with the use of the IMP, whether or not considered related to the IMP. This includes, for example, a significant or unexpected worsening of the condition under study, the exacerbation of a chronic or intermittent pre-existing condition, the detection or diagnosis of a new condition after IMP administration, or events that occur as a result of protocol- mandated procedures. The term “solicited adverse event”, as used herein, refers to a predefined list of adverse events that are proactively monitored during a clinical study due to their frequent occurrence as reactions to vaccines. In the context of the present invention, solicited AEs specifically include local injection site reactions such as pain, redness, and swelling, and systemic reactions such as fever, headache, shivering, fatigue, muscle pain (myalgia), joint pain (arthralgia), and gastrointestinal symptoms. By definition within the clinical protocol, all such solicited AEs are considered to be related to the IMP. The term “unsolicited adverse event” refers to an adverse event that is not part of the predefined list of solicited AEs and is spontaneously reported by a study participant or detected by an investigator. Unlike solicited AEs, each unsolicited AE is subject to a formal medical judgment by a blinded investigator or delegate to determine its causal relationship to the administration of the IMP. Based on a comprehensive review of all available clinical data, the unsolicited AE is thereby classified as either ‘related’ or ‘unrelated’ to the IMP. As used herein, the term “reactogenicity” refers to the physical manifestation of the inflammatory response to vaccination and is characterized by the occurrence of expected local and systemic adverse reactions. The reactogenicity profile of a vaccine is assessed by monitoring a predefined set of solicited adverse events within a specified time period following administration. The term “serious adverse event” or “SAE”, as used herein, refers to any adverse event that, at any dose, meets one or more of the following criteria: (a) results in death; (b) is life-threatening, meaning the participant was at risk of death at the time of the event; (c) requires inpatient hospitalization or prolongation of existing hospitalization; (d) results in persistent or significant disability or incapacity; (e) is a congenital anomaly or birth defect; or (f) is another important medical event that, based on medical or scientific judgment, may jeopardize the participant or may require medical or surgical intervention to prevent one of the other outcomes listed. Examples of such other important medical events include, but are not limited to, invasive or malignant cancers, allergic bronchospasm requiring intensive treatment, or blood dyscrasias or convulsions that do not result in hospitalization. As used herein, the terms “severity” or “intensity” of an adverse event are categorized into grades to provide an objective measure of the event’s impact. The specific criteria are defined by the context of the adverse event as follows: In the context of solicited systemic adverse events, severity is defined as: ^ Grade 1 (mild): The event is present and easily tolerated by the participant (e.g., for fever, a temperature of ≥ 38.0°C to ≤ 38.5°C). ^ Grade 2 (moderate): The event is present and interferes with normal activity (e.g., for fever, a temperature of > 38.5°C to ≤ 39.0°C). ^ Grade 3 (severe): The event is present and prevents normal activity (e.g., for fever, a temperature of > 39.0°C). In the context of solicited local adverse events, severity is defined as: ^ For pain: Grade 1 (mild) refers to pain that does not interfere with normal activity; Grade 2 (moderate) refers to pain that interferes with normal activity when the limb is moved; and Grade 3 (severe) refers to significant pain at rest that prevents normal activity. ^ For redness or swelling: Grade 1 (mild) refers to a diameter of > 25 mm to ≤ 50 mm; Grade 2 (moderate) refers to a diameter of > 50 mm to ≤ 100 mm; and Grade 3 (severe) refers to a diameter of > 100 mm. In the context of unsolicited adverse events, severity is defined as: ^ Grade 1 (mild): The AE is easily tolerated by the participant, causing minimal discomfort, and does not interfere with normal everyday activities. ^ Grade 2 (moderate): The AE is sufficiently discomforting to interfere with normal everyday activities. ^ Grade 3 (severe): The AE prevents normal everyday activities.Each embodiment described herein is to be applied mutatis mutandis to each other embodimentdescribed herein, unless specifically stated otherwise. Accordingly, the present invention specifically relates to each combination of features and embodiments described herein, including any combination of general and / or preferred features / embodiments. The present invention further relates to the following items: 1. A chimeric polypeptide comprising a respiratory syncytial virus (RSV) fusion protein and a structure-stabilizing moiety, wherein said RSV fusion protein comprises an amino acid sequence having at least about 90% sequence identity to the amino acid sequence set forth in SEQ ID NO: 26, wherein said RSV fusion protein comprises a C-terminal amino acid sequence consisting of the amino acid sequence IRK or IRR, wherein said structure-stabilizing moiety comprises a first heptad repeat region (FHRR) and a second heptad repeat region (SHRR), wherein said FHRR comprises an amino acid sequence having at least about 90% sequence identity to the amino acid sequence set forth in SEQ ID NO: 30, and wherein said SHRR comprises an amino acid sequence having at least about 90% sequence identity to the amino acid sequence set forth in SEQ ID NO: 31. The chimeric polypeptide according to item 1, wherein said RSV fusion protein comprises any one or more, preferably all, of the following amino acid residues: (i) a cysteine residue in position 87 in the amino acid sequence set forth in SEQ ID NO: 26 or at a position corresponding to said position; (ii) a cysteine residue in position 93 in the amino acid sequence set forth in SEQ ID NO: 26 or at a position corresponding to said position; (iii) a phenylalanine residue in position 128 in the amino acid sequence set forth in SEQ ID NO: 26 or at a position corresponding to said position; (iv) a leucine residue in position 145 in the amino acid sequence set forth in SEQ ID NO: 26 or at a position corresponding to said position; (v) a cysteine residue in position 228 in the amino acid sequence set forth in SEQ ID NO: 26 or at a position corresponding to said position; (vi) an arginine residue in position 311 in the amino acid sequence set forth in SEQ ID NO: 26 or at a position corresponding to said position; and (vii) a cysteine residue in position 396 in the amino acid sequence set forth in SEQ ID NO: 26 or at a position corresponding to said position. The chimeric polypeptide according to item 1 or 2, wherein said RSV fusion protein comprises a C- terminal amino acid sequence consisting of the amino acid sequence IRK. The chimeric polypeptide according to any one of items 1 to 3, wherein said RSV fusion protein comprises the amino acid sequence set forth in SEQ ID NO: 26. The chimeric polypeptide according to any one of items 1 to 4, wherein said FHRR and said SHRR are linked via a linker, preferably wherein said linker is a peptide linker. The chimeric polypeptide according to item 5, wherein said linker comprises an amino acid sequence selected from GGSGG (SEQ ID NO: 32), GSG, GS, GGSG (SEQ ID NO: 33), GSGS (SEQ ID NO: 34), AS, GGGS (SEQ ID NO: 35), G4S (SEQ ID NO: 36), (G4S)2 (SEQ ID NO: 37), (G4S)3 (SEQ ID NO: 38), (G4S)4 (SEQ ID NO: 39), G4SG (SEQ ID NO: 40), GSGG (SEQ ID NO: 41), and GSGGS (SEQ ID NO: 42). The chimeric polypeptide according to item 5 or 6, wherein said linker comprises the amino acid sequence GGSGG (SEQ ID NO: 32). 8. The chimeric polypeptide according to any one of items 1 to 7, wherein said structure-stabilizing moiety comprises an amino acid sequence having at least about 90% sequence identity to the amino acid sequence set forth in SEQ ID NO: 29. 9. The chimeric polypeptide according to item 8, wherein said structure-stabilizing moiety comprises the amino acid sequence set forth in SEQ ID NO: 29. 10. The chimeric polypeptide according to any one of items 1 to 9, wherein said RSV fusion protein and said structure-stabilizing moiety are linked via a linker, preferably wherein said linker is a peptide linker. 11. The chimeric polypeptide according to item 10, wherein said linker comprises an amino acid sequence selected from GSG, GS, GGSGG (SEQ ID NO: 32), GGSG (SEQ ID NO: 33), GSGS (SEQ ID NO: 34), AS, GGGS (SEQ ID NO: 35), G4S (SEQ ID NO: 36), (G4S)2 (SEQ ID NO: 37), (G4S)3 (SEQ ID NO: 38), (G4S)4 (SEQ ID NO: 39), G4SG (SEQ ID NO: 40), GSGG (SEQ ID NO: 41), and GSGGS (SEQ ID NO: 42). 12. The chimeric polypeptide according to item 11, wherein said linker comprises the amino acid sequence GSG. 13. The chimeric polypeptide according to any one of items 1 to 12, wherein said chimeric polypeptide comprises an amino acid sequence having at least about 90% sequence identity to the amino acid sequence set forth in SEQ ID NO: 27. 14. The chimeric polypeptide according to any one of items 1 to 13, wherein said chimeric polypeptide consists of the amino acid sequence set forth in SEQ ID NO: 27. 15. A nucleic acid comprising a nucleic acid sequence encoding the chimeric polypeptide according to any one of items 1 to 14. 16. The nucleic acid according to item 15, wherein said nucleic acid is a ribonucleic acid (RNA), preferably a messenger RNA (mRNA). 17. A composition comprising the chimeric polypeptide according to any one of items 1 to 14 or the nucleic acid according to item 15 or 16, preferably wherein said composition is a pharmaceutical composition. A kit comprising the chimeric polypeptide according to any one of items 1 to 14, the nucleic acid according to item 15 or 16, or the composition according to item 17. The chimeric polypeptide according to any one of items 1 to 14, the nucleic acid according to item 15 or 16, the composition according to item 17, or the kit according to item 18, for use in the immunization and / or the vaccination of a subject. A method for the immunization and / or the vaccination of a subject, wherein the method comprises administering the chimeric polypeptide according to any one of items 1 to 14, the nucleic acid according to item 15 or 16, the composition according to item 17, or the kit according to item 18 to said subject. Use of the chimeric polypeptide according to any one of items 1 to 14, or the nucleic acid according to item 15 or 16, in the manufacture of a medicament for the immunization and / or the vaccination of a subject. The chimeric polypeptide according to any one of items 1 to 14, the nucleic acid according to item 15 or 16, the composition according to item 17, or the kit according to item 18, for use in the prevention of an RSV infection. A method for the prevention of an RSV infection, wherein the method comprises administering the chimeric polypeptide according to any one of items 1 to 14, the nucleic acid according to item 15 or 16, the composition according to item 17, or the kit according to item 18 to a subject in need thereof. Use of the chimeric polypeptide according to any one of items 1 to 14, or the nucleic acid according to item 15 or 16, in the manufacture of a medicament for the prevention of an RSV infection. A nucleic acid vector comprising the nucleic acid according to item 15. A host cell comprising the nucleic acid according to item 15 or 16, and / or the nucleic acid vector according to item 25. A method of production of a chimeric polypeptide, wherein the method comprises: (i) culturing the host cell according to item 26; or (ii) expressing a chimeric polypeptide from the nucleic acid according to item 15 or 16, and / or the nucleic acid vector according to item 25, optionally in a cell-free transcription- translation system. 28. A method of production of an antigen-binding molecule that specifically binds to an RSV fusion protein, the method comprising: (i) immunizing an animal with the chimeric polypeptide according to any one of items 1 to 14, or the nucleic acid according to item 15 or 16, or the composition according to item 17; (ii) identifying and / or isolating a B cell from the immunized animal, which specifically binds to the RSV fusion protein; and (iii) producing the antigen-binding molecule expressed by that B cell. 29. An antigen-binding molecule obtainable by the method according to item 28. The invention is also described by the following illustrative and non-limiting figures. The appended figures show:Figure 1. Yield of antigen panels listed in Table 3 as determined post-purification via absorbance at280nm. Results are from at least 2 different expressions. Data presented as mean + / - standard deviation. Figure 2. Yield of selected lead MC2S stabilised RSV F antigen S508 (SEQ ID NO: 17), compared to best-in-class comparators; DS Cav1 Foldon (“DSCav1”; SEQ ID NO: 23; Joyce, Zhang et al.2016) and SC9-10 AYDS Cav1 Foldon (“SC9-10DSCav1AY”; SEQ ID NO: 2; McLellan, Chen et al.2013). Yields are determinedby absorbance at 280nm from at least 2 different expressions. Data presented as mean + / - standard deviation. Figure 3. SDS-PAGE of (Left; “Time 0”) freshly purified Fsol (“RSV Fsol”; SEQ ID NO: 24), DS Cav1 (“DSCav”;SEQ ID NO: 23; Joyce, Zhang et al. 2016), SC9-10AY DS Cav1 Foldon (“SC910AY fd”; SEQ ID NO: 2;McLellan, Chen et al.2013), and S508 (SEQ ID NO: 17), and (Right) following incubation of the antigensat 25 or 40°C for 7 days. Molecular weight markers are displayed in the first and last lane of each SDS- PAGE, with kDa shown on the left.Figure 4. Size exclusion chromatography (SEC) analysis of freshly purified Fsol (SEQ ID NO: 24;Bermingham et al., 2018), DS Cav1 (“DSCav1 Fd”; SEQ ID NO: 23; Joyce, Zhang et al.2016), SC9-10AY DSCav1 Foldon (“SC9-10 DSCavAY”; SEQ ID NO: 2; McLellan, Chen et al. 2013), and S508 (SEQ ID NO: 17)prior to (“Time 0") or following incubation at 25 or 40°C for 7 days. Figure 5. Comparison of kD values calculated by ELISA for freshly purified Fsol (SEQ ID NO: 24), DS Cav1(“DSCav1”; SEQ ID NO: 23; Joyce, Zhang et al. 2016), SC9-10AY DS Cav1 Foldon (“SC9-10 DSCav1 AY”;SEQ ID NO: 2; McLellan, Chen et al. 2013), and S508 (SEQ ID NO: 17) prior to (“Time 0") or followingincubation at 25 or 40°C for 7 days. Data presented as mean + / - standard deviation. Figure 6. S508 (SEQ ID NO: 17) manufacturing yield from clonal cell line fed-batch production (top) and liquid stability of S508 drug product (bottom) over 6 months as quantified by different methods. Data presented as mean + / - standard deviation.Figure 7. Accelerated stability analysis of S508 (SEQ ID NO: 17), Arexvy® (GSK; Papi, Ison et al.2023) andAbrysvo® (Pfizer; Walsh, Perez Marc et al. 2023) by ELISA. Data presented as mean + / - standarddeviation. Figure 8. Neutralization of RSV strain A2 of mouse sera following administration of two doses of S508(SEQ ID NO: 17) or Arexvy® antigen (GSK; Papi, Ison et al.2023) with AddaVaxTM adjuvant. Data presentedas geometric mean + / - geometric standard deviation.Figure 9. Immunogenicity in BALB / c mice. (A) Serum IgG titre to the RSV F antigens (black), and the IgGtitre specific to either the foldon or MC2S trimer stabilising domain (grey). Titres were determined byELISA and expressed as EC50 values. (B) Relative proportion of foldon / MC2S reactivity calculated as apercentage of the total antigen specific titre.Figure 10. Ability of RSV antigens to deplete neutralizing antibodies form human plasma. RSV PRNT50with titration of pooled human plasma (black circles) and human plasma pre-incubated with 0.5 µg / mL of RSV Fsol (grey diamond), DSCav1 (black square), or VXB-213 (“S508”; grey triangle).Figure 11. Antigen Stability in liquid formulation. RSV S508 stability analysis out to 12 months at 2-8°Cas determined by percentage of product as a single MW by reduced CE-SDS, SE-HPLC, or by potency testing capture ELISA with paired neutralising antibodies.Figure 12. (A) RSV-A and (B) RSV-B Neutralisation Titre prior to vaccination (Baseline) and at 30 daysfollowing vaccination with either Placebo, Arexvy (GSK) or VXB-241 at 4 doses levels (60 µg, 120 µg, 240 µg or 480 µg).Figure 13. (A) hMPV-A and (B) hMPV-B Neutralisation Titre prior to vaccination (“Baseline”) and at 30days following vaccination with either Placebo, Arexvy (GSK) or VXB-241 at 4 doses levels (60 µg, 120 µg, 240 µg or 480 µg; “Day30”). List of sequences The present invention further provides the following amino acid sequences, which are also described in the concurrently filed sequence listing forming part of the present specification. It will be understood that the present invention relates to the sequences disclosed herein, including in the following list of sequences, as well as the sequences disclosed in the concurrently filed sequence listing. In case of any discrepancy between any one of the sequences disclosed in the present specification, including in the list of sequences herein below, and the corresponding sequence disclosed in the sequence listing, the present invention specifically and individually relates to each one of the respective sequences. SEQ ID NO: 1 RSV Fusion protein full length Also referred to as ‘FWT’ MELLILKANAITTILTAVTFCFASGQNITEEFYQSTCSAVSKGYLSALRTGWYTSVITIELSNIKKNKCNGTDAKVKLIKQEL DKYKNAVTELQLLMQSTQATNNRARRELPRFMNYTLNNAKKTNVTLSKKRKRRFLGFLLGVGSAIASGVAVSKVLHLE GEVNKIKSALLSTNKAVVSLSNGVSVLTSKVLDLKNYIDKQLLPIVNKQSCSISNIETVIEFQQKNNRLLEITREFSVNAGV TTPVSTYMLTNSELLSLINDMPITNDQKKLMSNNVQIVRQQSYSIMSIIKEEVLAYVVQLPLYGVIDTPCWKLHTSPLCT TNTKEGSNICLTRTDRGWYCDNAGSVSFFPQAETCKVQSNRVFCDTMNSLTLPSEVNLCNVDIFNPKYDCKIMTSKTD VSSSVITSLGAIVSCYGKTKCTASNKNRGIIKTFSNGCDYVSNKGVDTVSVGNTLYYVNKQEGKSLYVKGEPIINFYDPLV FPSDEFDASISQVNEKINQSLAFIRKSDELLHNVNAGKSTTNIMITTIIIVIIVILLSLIAVGLLLYCKARSTPFTLSKDQLSGI NNIAFSN wherein: ^Italicized text corresponds to the signal peptide of RSV Fusion protein;^ Bold text is the transmembrane domain; and^ Underlined text is the cytoplasmic domain.SEQ ID NO: 2 RSV Fusion protein SC9-10 AY DS Cav1 Foldon (Joyce et al., Nat Struct Mol Biol 2016 DOI: 10.1038 / nsmb.3267) Also referred to as ‘SC9-10 AY DS Cav1 Foldon’ MELLILKANAITTILTAVTFCFASGQNITEEFYQSTCSAVSKGYLSALRTGWYTSVITIELSNIKENKCNGTDAKVKLIKQEL DKYKNAVTELQLLMQSTPATGSGSAICSGVAVCKVLHLEGEVNKIKSALLSTNKAVVSLSNGVSVLTFKVLDLKNYIDKQ LLPILNKQSCSISNIETVIEFQQKNNRLLEITREFSVNAGVTTPVSTYMLTNSELLSLINDMPITNDQKKLMSNNVQIVRQ QSYSIMCIIKEEVLAYVVQLPLYGVIDTPCWKLHTSPLCTTNTKEGSNICLTRTDRGWYCDNAGSVSFFPQAETCKVQS NRVFCDTMNSRTLPSEVNLCNVDIFNPKYDCKIMTSKTDVSSSVITSLGAIVSCYGKTKCTASNKNRGIIKTFSNGCDYV SNKGVDTVSVGNTLYCVNKQEGKSLYVKGEPIINFYDPLVFPSDEFDASISQVNEKINQSLAFIRKSDELLSAIGGYIPEAP RDGQAYVRKDGEWVLLSTFLGGLVPR wherein: ^Italicized text corresponds to the signal peptide of RSV Fusion protein;^ Bold text is a flexible linker; and^ Underlined text corresponds to Foldon SSM.SEQ ID NO: 3 RSV Fwt-504-CT5S Also referred to as ‘F504’ MELLILKANAITTILTAVTFCFASGQNITEEFYQSTCSAVSKGYLSALRTGWYTSVITIELSNIKKNKCNGTDAKVKLIKQEL DKYKNAVTELQLLMQSTQATNNRARRELPRFMNYTLNNAKKTNVTLSKKRKRRFLGFLLGVGSAIASGVAVSKVLHLE GEVNKIKSALLSTNKAVVSLSNGVSVLTSKVLDLKNYIDKQLLPIVNKQSCSISNIETVIEFQQKNNRLLEITREFSVNAGV TTPVSTYMLTNSELLSLINDMPITNDQKKLMSNNVQIVRQQSYSIMSIIKEEVLAYVVQLPLYGVIDTPCWKLHTSPLCT TNTKEGSNICLTRTDRGWYCDNAGSVSFFPQAETCKVQSNRVFCDTMNSLTLPSEVNLCNVDIFNPKYDCKIMTSKTD VSSSVITSLGAIVSCYGKTKCTASNKNRGIIKTFSNGCDYVSNKGVDTVSVGNTLYYVNKQEGKSLYVKGEPIINFYDPLV FPSDEFDASISQVNEKINQSLAGSGLANATAAQQEVLEAQYAMVQHIAKGIRILEARVARGGSGGNHTTWQQWEEE IENHTGNLTLLLREAANQTHIAQRDARRI wherein: ^Italicized text corresponds to the signal peptide of RSV Fusion protein;^ Bold text is a flexible linker; and^ Underlined text corresponds to the MC2S SSM.SEQ ID NO: 4 RSV Fwt-505-CT5S Also referred to as ‘F505’ MELLILKANAITTILTAVTFCFASGQNITEEFYQSTCSAVSKGYLSALRTGWYTSVITIELSNIKKNKCNGTDAKVKLIKQEL DKYKNAVTELQLLMQSTQATNNRARRELPRFMNYTLNNAKKTNVTLSKKRKRRFLGFLLGVGSAIASGVAVSKVLHLE GEVNKIKSALLSTNKAVVSLSNGVSVLTSKVLDLKNYIDKQLLPIVNKQSCSISNIETVIEFQQKNNRLLEITREFSVNAGV TTPVSTYMLTNSELLSLINDMPITNDQKKLMSNNVQIVRQQSYSIMSIIKEEVLAYVVQLPLYGVIDTPCWKLHTSPLCT TNTKEGSNICLTRTDRGWYCDNAGSVSFFPQAETCKVQSNRVFCDTMNSLTLPSEVNLCNVDIFNPKYDCKIMTSKTD VSSSVITSLGAIVSCYGKTKCTASNKNRGIIKTFSNGCDYVSNKGVDTVSVGNTLYYVNKQEGKSLYVKGEPIINFYDPLV FPSDEFDASISQVNEKINQSLAFGSGLANATAAQQEVLEAQYAMVQHIAKGIRILEARVARGGSGGNHTTWQQWEE EIENHTGNLTLLLREAANQTHIAQRDARRI wherein: ^Italicized text corresponds to the signal peptide of RSV Fusion protein;^ Bold text is a flexible linker; and^ Underlined text corresponds to the MC2S SSM.SEQ ID NO: 5 RSV Fwt-506-CT5S Also referred to as ‘F506’ MELLILKANAITTILTAVTFCFASGQNITEEFYQSTCSAVSKGYLSALRTGWYTSVITIELSNIKKNKCNGTDAKVKLIKQEL DKYKNAVTELQLLMQSTQATNNRARRELPRFMNYTLNNAKKTNVTLSKKRKRRFLGFLLGVGSAIASGVAVSKVLHLE GEVNKIKSALLSTNKAVVSLSNGVSVLTSKVLDLKNYIDKQLLPIVNKQSCSISNIETVIEFQQKNNRLLEITREFSVNAGV TTPVSTYMLTNSELLSLINDMPITNDQKKLMSNNVQIVRQQSYSIMSIIKEEVLAYVVQLPLYGVIDTPCWKLHTSPLCT TNTKEGSNICLTRTDRGWYCDNAGSVSFFPQAETCKVQSNRVFCDTMNSLTLPSEVNLCNVDIFNPKYDCKIMTSKTD VSSSVITSLGAIVSCYGKTKCTASNKNRGIIKTFSNGCDYVSNKGVDTVSVGNTLYYVNKQEGKSLYVKGEPIINFYDPLV FPSDEFDASISQVNEKINQSLAFIGSGLANATAAQQEVLEAQYAMVQHIAKGIRILEARVARGGSGGNHTTWQQWE EEIENHTGNLTLLLREAANQTHIAQRDARRI wherein: ^Italicized text corresponds to the signal peptide of RSV Fusion protein;^ Bold text is a flexible linker; and^ Underlined text corresponds to the MC2S SSM.SEQ ID NO: 6 RSV Fwt-507-CT5S Also referred to as ‘F507’ MELLILKANAITTILTAVTFCFASGQNITEEFYQSTCSAVSKGYLSALRTGWYTSVITIELSNIKKNKCNGTDAKVKLIKQEL DKYKNAVTELQLLMQSTQATNNRARRELPRFMNYTLNNAKKTNVTLSKKRKRRFLGFLLGVGSAIASGVAVSKVLHLE GEVNKIKSALLSTNKAVVSLSNGVSVLTSKVLDLKNYIDKQLLPIVNKQSCSISNIETVIEFQQKNNRLLEITREFSVNAGV TTPVSTYMLTNSELLSLINDMPITNDQKKLMSNNVQIVRQQSYSIMSIIKEEVLAYVVQLPLYGVIDTPCWKLHTSPLCT TNTKEGSNICLTRTDRGWYCDNAGSVSFFPQAETCKVQSNRVFCDTMNSLTLPSEVNLCNVDIFNPKYDCKIMTSKTD VSSSVITSLGAIVSCYGKTKCTASNKNRGIIKTFSNGCDYVSNKGVDTVSVGNTLYYVNKQEGKSLYVKGEPIINFYDPLV FPSDEFDASISQVNEKINQSLAFIRGSGLANATAAQQEVLEAQYAMVQHIAKGIRILEARVARGGSGGNHTTWQQW EEEIENHTGNLTLLLREAANQTHIAQRDARRI wherein: ^Italicized text corresponds to the signal peptide of RSV Fusion protein;^ Bold text is a flexible linker; and^ Underlined text corresponds to the MC2S SSM.SEQ ID NO: 7 RSV Fwt-508-CT5S Also referred to as ‘F508’ MELLILKANAITTILTAVTFCFASGQNITEEFYQSTCSAVSKGYLSALRTGWYTSVITIELSNIKKNKCNGTDAKVKLIKQEL DKYKNAVTELQLLMQSTQATNNRARRELPRFMNYTLNNAKKTNVTLSKKRKRRFLGFLLGVGSAIASGVAVSKVLHLE GEVNKIKSALLSTNKAVVSLSNGVSVLTSKVLDLKNYIDKQLLPIVNKQSCSISNIETVIEFQQKNNRLLEITREFSVNAGV TTPVSTYMLTNSELLSLINDMPITNDQKKLMSNNVQIVRQQSYSIMSIIKEEVLAYVVQLPLYGVIDTPCWKLHTSPLCT TNTKEGSNICLTRTDRGWYCDNAGSVSFFPQAETCKVQSNRVFCDTMNSLTLPSEVNLCNVDIFNPKYDCKIMTSKTD VSSSVITSLGAIVSCYGKTKCTASNKNRGIIKTFSNGCDYVSNKGVDTVSVGNTLYYVNKQEGKSLYVKGEPIINFYDPLV FPSDEFDASISQVNEKINQSLAFIRKGSGLANATAAQQEVLEAQYAMVQHIAKGIRILEARVARGGSGGNHTTWQQ WEEEIENHTGNLTLLLREAANQTHIAQRDARRI wherein: ^Italicized text corresponds to the signal peptide of RSV Fusion protein;^ Bold text is a flexible linker; and^ Underlined text corresponds to the MC2S SSM.SEQ ID NO: 8 RSV Fwt-509-CT5S Also referred to as ‘F509’ MELLILKANAITTILTAVTFCFASGQNITEEFYQSTCSAVSKGYLSALRTGWYTSVITIELSNIKKNKCNGTDAKVKLIKQEL DKYKNAVTELQLLMQSTQATNNRARRELPRFMNYTLNNAKKTNVTLSKKRKRRFLGFLLGVGSAIASGVAVSKVLHLE GEVNKIKSALLSTNKAVVSLSNGVSVLTSKVLDLKNYIDKQLLPIVNKQSCSISNIETVIEFQQKNNRLLEITREFSVNAGV TTPVSTYMLTNSELLSLINDMPITNDQKKLMSNNVQIVRQQSYSIMSIIKEEVLAYVVQLPLYGVIDTPCWKLHTSPLCT TNTKEGSNICLTRTDRGWYCDNAGSVSFFPQAETCKVQSNRVFCDTMNSLTLPSEVNLCNVDIFNPKYDCKIMTSKTD VSSSVITSLGAIVSCYGKTKCTASNKNRGIIKTFSNGCDYVSNKGVDTVSVGNTLYYVNKQEGKSLYVKGEPIINFYDPLV FPSDEFDASISQVNEKINQSLAFIRKSGSGLANATAAQQEVLEAQYAMVQHIAKGIRILEARVARGGSGGNHTTWQQ WEEEIENHTGNLTLLLREAANQTHIAQRDARRI wherein: ^Italicized text corresponds to the signal peptide of RSV Fusion protein;^ Bold text is a flexible linker; and^ Underlined text corresponds to the MC2S SSM.SEQ ID NO: 9 RSV Fwt-510-CT5S Also referred to as ‘F510’ MELLILKANAITTILTAVTFCFASGQNITEEFYQSTCSAVSKGYLSALRTGWYTSVITIELSNIKKNKCNGTDAKVKLIKQEL DKYKNAVTELQLLMQSTQATNNRARRELPRFMNYTLNNAKKTNVTLSKKRKRRFLGFLLGVGSAIASGVAVSKVLHLE GEVNKIKSALLSTNKAVVSLSNGVSVLTSKVLDLKNYIDKQLLPIVNKQSCSISNIETVIEFQQKNNRLLEITREFSVNAGV TTPVSTYMLTNSELLSLINDMPITNDQKKLMSNNVQIVRQQSYSIMSIIKEEVLAYVVQLPLYGVIDTPCWKLHTSPLCT TNTKEGSNICLTRTDRGWYCDNAGSVSFFPQAETCKVQSNRVFCDTMNSLTLPSEVNLCNVDIFNPKYDCKIMTSKTD VSSSVITSLGAIVSCYGKTKCTASNKNRGIIKTFSNGCDYVSNKGVDTVSVGNTLYYVNKQEGKSLYVKGEPIINFYDPLV FPSDEFDASISQVNEKINQSLAFIRKSDGSGLANATAAQQEVLEAQYAMVQHIAKGIRILEARVARGGSGGNHTTWQ QWEEEIENHTGNLTLLLREAANQTHIAQRDARRI wherein: ^Italicized text corresponds to the signal peptide of RSV Fusion protein;^ Bold text is a flexible linker; and^ Underlined text corresponds to the MC2S SSM. SEQ ID NO: 10 RSV Fwt-511-CT5S Also referred to as ‘F511’ MELLILKANAITTILTAVTFCFASGQNITEEFYQSTCSAVSKGYLSALRTGWYTSVITIELSNIKKNKCNGTDAKVKLIKQEL DKYKNAVTELQLLMQSTQATNNRARRELPRFMNYTLNNAKKTNVTLSKKRKRRFLGFLLGVGSAIASGVAVSKVLHLE GEVNKIKSALLSTNKAVVSLSNGVSVLTSKVLDLKNYIDKQLLPIVNKQSCSISNIETVIEFQQKNNRLLEITREFSVNAGV TTPVSTYMLTNSELLSLINDMPITNDQKKLMSNNVQIVRQQSYSIMSIIKEEVLAYVVQLPLYGVIDTPCWKLHTSPLCT TNTKEGSNICLTRTDRGWYCDNAGSVSFFPQAETCKVQSNRVFCDTMNSLTLPSEVNLCNVDIFNPKYDCKIMTSKTD VSSSVITSLGAIVSCYGKTKCTASNKNRGIIKTFSNGCDYVSNKGVDTVSVGNTLYYVNKQEGKSLYVKGEPIINFYDPLV FPSDEFDASISQVNEKINQSLAFIRKSDEGSGLANATAAQQEVLEAQYAMVQHIAKGIRILEARVARGGSGGNHTTW QQWEEEIENHTGNLTLLLREAANQTHIAQRDARRI wherein: ^Italicized text corresponds to the signal peptide of RSV Fusion protein;^ Bold text is a flexible linker; and^ Underlined text corresponds to the MC2S SSM.SEQ ID NO: 11 RSV Fwt-512-CT5S Also referred to as ‘F512’ MELLILKANAITTILTAVTFCFASGQNITEEFYQSTCSAVSKGYLSALRTGWYTSVITIELSNIKKNKCNGTDAKVKLIKQEL DKYKNAVTELQLLMQSTQATNNRARRELPRFMNYTLNNAKKTNVTLSKKRKRRFLGFLLGVGSAIASGVAVSKVLHLE GEVNKIKSALLSTNKAVVSLSNGVSVLTSKVLDLKNYIDKQLLPIVNKQSCSISNIETVIEFQQKNNRLLEITREFSVNAGV TTPVSTYMLTNSELLSLINDMPITNDQKKLMSNNVQIVRQQSYSIMSIIKEEVLAYVVQLPLYGVIDTPCWKLHTSPLCT TNTKEGSNICLTRTDRGWYCDNAGSVSFFPQAETCKVQSNRVFCDTMNSLTLPSEVNLCNVDIFNPKYDCKIMTSKTD VSSSVITSLGAIVSCYGKTKCTASNKNRGIIKTFSNGCDYVSNKGVDTVSVGNTLYYVNKQEGKSLYVKGEPIINFYDPLV FPSDEFDASISQVNEKINQSLAFIRKSDELGSGLANATAAQQEVLEAQYAMVQHIAKGIRILEARVARGGSGGNHTTW QQWEEEIENHTGNLTLLLREAANQTHIAQRDARRI wherein: ^Italicized text corresponds to the signal peptide of RSV Fusion protein;^ Bold text is a flexible linker; and^ Underlined text corresponds to the MC2S SSM.SEQ ID NO: 12 RSV Fwt-513-CT5S Also referred to as ‘F513’ MELLILKANAITTILTAVTFCFASGQNITEEFYQSTCSAVSKGYLSALRTGWYTSVITIELSNIKKNKCNGTDAKVKLIKQEL DKYKNAVTELQLLMQSTQATNNRARRELPRFMNYTLNNAKKTNVTLSKKRKRRFLGFLLGVGSAIASGVAVSKVLHLE GEVNKIKSALLSTNKAVVSLSNGVSVLTSKVLDLKNYIDKQLLPIVNKQSCSISNIETVIEFQQKNNRLLEITREFSVNAGV TTPVSTYMLTNSELLSLINDMPITNDQKKLMSNNVQIVRQQSYSIMSIIKEEVLAYVVQLPLYGVIDTPCWKLHTSPLCT TNTKEGSNICLTRTDRGWYCDNAGSVSFFPQAETCKVQSNRVFCDTMNSLTLPSEVNLCNVDIFNPKYDCKIMTSKTD VSSSVITSLGAIVSCYGKTKCTASNKNRGIIKTFSNGCDYVSNKGVDTVSVGNTLYYVNKQEGKSLYVKGEPIINFYDPLV FPSDEFDASISQVNEKINQSLAFIRKSDELLGSGLANATAAQQEVLEAQYAMVQHIAKGIRILEARVARGGSGGNHTT WQQWEEEIENHTGNLTLLLREAANQTHIAQRDARRI wherein: ^Italicized text corresponds to the signal peptide of RSV Fusion protein;^ Bold text is a flexible linker; and^ Underlined text corresponds to the MC2S SSM.SEQ ID NO: 13 RSV F SC9-10AY-504-CT5S Also referred to as ‘S504’ MELLILKANAITTILTAVTFCFASGQNITEEFYQSTCSAVSKGYLSALRTGWYTSVITIELSNIKENKCNGTDAKVKLIKQEL DKYKNAVTELQLLMQSTPATGSGSAICSGVAVCKVLHLEGEVNKIKSALLSTNKAVVSLSNGVSVLTFKVLDLKNYIDKQ LLPILNKQSCSISNIETVIEFQQKNNRLLEITREFSVNAGVTTPVSTYMLTNSELLSLINDMPITNDQKKLMSNNVQIVRQ QSYSIMCIIKEEVLAYVVQLPLYGVIDTPCWKLHTSPLCTTNTKEGSNICLTRTDRGWYCDNAGSVSFFPQAETCKVQS NRVFCDTMNSRTLPSEVNLCNVDIFNPKYDCKIMTSKTDVSSSVITSLGAIVSCYGKTKCTASNKNRGIIKTFSNGCDYV SNKGVDTVSVGNTLYCVNKQEGKSLYVKGEPIINFYDPLVFPSDEFDASISQVNEKINQSLAGSGLANATAAQQEVLEA QYAMVQHIAKGIRILEARVARGGSGGNHTTWQQWEEEIENHTGNLTLLLREAANQTHIAQRDARRI wherein: ^Italicized text corresponds to the signal peptide of RSV Fusion protein;^ Bold text is a flexible linker; and^ Underlined text corresponds to the MC2S SSM.SEQ ID NO: 14 RSV F SC9-10AY-505-CT5S Also referred to as ‘S505’ MELLILKANAITTILTAVTFCFASGQNITEEFYQSTCSAVSKGYLSALRTGWYTSVITIELSNIKENKCNGTDAKVKLIKQEL DKYKNAVTELQLLMQSTPATGSGSAICSGVAVCKVLHLEGEVNKIKSALLSTNKAVVSLSNGVSVLTFKVLDLKNYIDKQ LLPILNKQSCSISNIETVIEFQQKNNRLLEITREFSVNAGVTTPVSTYMLTNSELLSLINDMPITNDQKKLMSNNVQIVRQ QSYSIMCIIKEEVLAYVVQLPLYGVIDTPCWKLHTSPLCTTNTKEGSNICLTRTDRGWYCDNAGSVSFFPQAETCKVQS NRVFCDTMNSRTLPSEVNLCNVDIFNPKYDCKIMTSKTDVSSSVITSLGAIVSCYGKTKCTASNKNRGIIKTFSNGCDYV SNKGVDTVSVGNTLYCVNKQEGKSLYVKGEPIINFYDPLVFPSDEFDASISQVNEKINQSLAFGSGLANATAAQQEVLE AQYAMVQHIAKGIRILEARVARGGSGGNHTTWQQWEEEIENHTGNLTLLLREAANQTHIAQRDARRI wherein: ^Italicized text corresponds to the signal peptide of RSV Fusion protein;^ Bold text is a flexible linker; and^ Underlined text corresponds to the MC2S SSM. SEQ ID NO: 15 RSV F SC9-10AY-506-CT5S Also referred to as ‘S506’ MELLILKANAITTILTAVTFCFASGQNITEEFYQSTCSAVSKGYLSALRTGWYTSVITIELSNIKENKCNGTDAKVKLIKQEL DKYKNAVTELQLLMQSTPATGSGSAICSGVAVCKVLHLEGEVNKIKSALLSTNKAVVSLSNGVSVLTFKVLDLKNYIDKQ LLPILNKQSCSISNIETVIEFQQKNNRLLEITREFSVNAGVTTPVSTYMLTNSELLSLINDMPITNDQKKLMSNNVQIVRQ QSYSIMCIIKEEVLAYVVQLPLYGVIDTPCWKLHTSPLCTTNTKEGSNICLTRTDRGWYCDNAGSVSFFPQAETCKVQS NRVFCDTMNSRTLPSEVNLCNVDIFNPKYDCKIMTSKTDVSSSVITSLGAIVSCYGKTKCTASNKNRGIIKTFSNGCDYV SNKGVDTVSVGNTLYCVNKQEGKSLYVKGEPIINFYDPLVFPSDEFDASISQVNEKINQSLAFIGSGLANATAAQQEVLE AQYAMVQHIAKGIRILEARVARGGSGGNHTTWQQWEEEIENHTGNLTLLLREAANQTHIAQRDARRI wherein: ^Italicized text corresponds to the signal peptide of RSV Fusion protein;^ Bold text is a flexible linker; and^ Underlined text corresponds to the MC2S SSM.SEQ ID NO: 16 RSV F SC9-10AY-507-CT5S Also referred to as ‘S507’ MELLILKANAITTILTAVTFCFASGQNITEEFYQSTCSAVSKGYLSALRTGWYTSVITIELSNIKENKCNGTDAKVKLIKQEL DKYKNAVTELQLLMQSTPATGSGSAICSGVAVCKVLHLEGEVNKIKSALLSTNKAVVSLSNGVSVLTFKVLDLKNYIDKQ LLPILNKQSCSISNIETVIEFQQKNNRLLEITREFSVNAGVTTPVSTYMLTNSELLSLINDMPITNDQKKLMSNNVQIVRQ QSYSIMCIIKEEVLAYVVQLPLYGVIDTPCWKLHTSPLCTTNTKEGSNICLTRTDRGWYCDNAGSVSFFPQAETCKVQS NRVFCDTMNSRTLPSEVNLCNVDIFNPKYDCKIMTSKTDVSSSVITSLGAIVSCYGKTKCTASNKNRGIIKTFSNGCDYV SNKGVDTVSVGNTLYCVNKQEGKSLYVKGEPIINFYDPLVFPSDEFDASISQVNEKINQSLAFIRGSGLANATAAQQEV LEAQYAMVQHIAKGIRILEARVARGGSGGNHTTWQQWEEEIENHTGNLTLLLREAANQTHIAQRDARRI wherein: ^Italicized text corresponds to the signal peptide of RSV Fusion protein;^ Bold text is a flexible linker; and^ Underlined text corresponds to the MC2S SSM.SEQ ID NO: 17 RSV F SC9-10AY-508-CT5S Also referred to as ‘S508’ MELLILKANAITTILTAVTFCFASGQNITEEFYQSTCSAVSKGYLSALRTGWYTSVITIELSNIKENKCNGTDAKVKLIKQEL DKYKNAVTELQLLMQSTPATGSGSAICSGVAVCKVLHLEGEVNKIKSALLSTNKAVVSLSNGVSVLTFKVLDLKNYIDKQ LLPILNKQSCSISNIETVIEFQQKNNRLLEITREFSVNAGVTTPVSTYMLTNSELLSLINDMPITNDQKKLMSNNVQIVRQ QSYSIMCIIKEEVLAYVVQLPLYGVIDTPCWKLHTSPLCTTNTKEGSNICLTRTDRGWYCDNAGSVSFFPQAETCKVQS NRVFCDTMNSRTLPSEVNLCNVDIFNPKYDCKIMTSKTDVSSSVITSLGAIVSCYGKTKCTASNKNRGIIKTFSNGCDYV SNKGVDTVSVGNTLYCVNKQEGKSLYVKGEPIINFYDPLVFPSDEFDASISQVNEKINQSLAFIRKGSGLANATAAQQE VLEAQYAMVQHIAKGIRILEARVARGGSGGNHTTWQQWEEEIENHTGNLTLLLREAANQTHIAQRDARRI wherein: ^Italicized text corresponds to the signal peptide of RSV Fusion protein;^ Bold text is a flexible linker; and^ Underlined text corresponds to the MC2S SSM.SEQ ID NO: 18 RSV F SC9-10AY-509-CT5S Also referred to as ‘S509’ MELLILKANAITTILTAVTFCFASGQNITEEFYQSTCSAVSKGYLSALRTGWYTSVITIELSNIKENKCNGTDAKVKLIKQEL DKYKNAVTELQLLMQSTPATGSGSAICSGVAVCKVLHLEGEVNKIKSALLSTNKAVVSLSNGVSVLTFKVLDLKNYIDKQ LLPILNKQSCSISNIETVIEFQQKNNRLLEITREFSVNAGVTTPVSTYMLTNSELLSLINDMPITNDQKKLMSNNVQIVRQ QSYSIMCIIKEEVLAYVVQLPLYGVIDTPCWKLHTSPLCTTNTKEGSNICLTRTDRGWYCDNAGSVSFFPQAETCKVQS NRVFCDTMNSRTLPSEVNLCNVDIFNPKYDCKIMTSKTDVSSSVITSLGAIVSCYGKTKCTASNKNRGIIKTFSNGCDYV SNKGVDTVSVGNTLYCVNKQEGKSLYVKGEPIINFYDPLVFPSDEFDASISQVNEKINQSLAFIRKSGSGLANATAAQQ EVLEAQYAMVQHIAKGIRILEARVARGGSGGNHTTWQQWEEEIENHTGNLTLLLREAANQTHIAQRDARRI wherein: ^Italicized text corresponds to the signal peptide of RSV Fusion protein;^ Bold text is a flexible linker; and^ Underlined text corresponds to the MC2S SSM.SEQ ID NO: 19 RSV F SC9-10AY-510-CT5S Also referred to as ‘S510’ MELLILKANAITTILTAVTFCFASGQNITEEFYQSTCSAVSKGYLSALRTGWYTSVITIELSNIKENKCNGTDAKVKLIKQEL DKYKNAVTELQLLMQSTPATGSGSAICSGVAVCKVLHLEGEVNKIKSALLSTNKAVVSLSNGVSVLTFKVLDLKNYIDKQ LLPILNKQSCSISNIETVIEFQQKNNRLLEITREFSVNAGVTTPVSTYMLTNSELLSLINDMPITNDQKKLMSNNVQIVRQ QSYSIMCIIKEEVLAYVVQLPLYGVIDTPCWKLHTSPLCTTNTKEGSNICLTRTDRGWYCDNAGSVSFFPQAETCKVQS NRVFCDTMNSRTLPSEVNLCNVDIFNPKYDCKIMTSKTDVSSSVITSLGAIVSCYGKTKCTASNKNRGIIKTFSNGCDYV SNKGVDTVSVGNTLYCVNKQEGKSLYVKGEPIINFYDPLVFPSDEFDASISQVNEKINQSLAFIRKSDGSGLANATAAQ QEVLEAQYAMVQHIAKGIRILEARVARGGSGGNHTTWQQWEEEIENHTGNLTLLLREAANQTHIAQRDARRI wherein: ^Italicized text corresponds to the signal peptide of RSV Fusion protein;^ Bold text is a flexible linker; and^ Underlined text corresponds to the MC2S SSM.SEQ ID NO: 20 RSV F SC9-10AY-511-CT5S Also referred to as ‘S511’ MELLILKANAITTILTAVTFCFASGQNITEEFYQSTCSAVSKGYLSALRTGWYTSVITIELSNIKENKCNGTDAKVKLIKQEL DKYKNAVTELQLLMQSTPATGSGSAICSGVAVCKVLHLEGEVNKIKSALLSTNKAVVSLSNGVSVLTFKVLDLKNYIDKQ LLPILNKQSCSISNIETVIEFQQKNNRLLEITREFSVNAGVTTPVSTYMLTNSELLSLINDMPITNDQKKLMSNNVQIVRQ QSYSIMCIIKEEVLAYVVQLPLYGVIDTPCWKLHTSPLCTTNTKEGSNICLTRTDRGWYCDNAGSVSFFPQAETCKVQS NRVFCDTMNSRTLPSEVNLCNVDIFNPKYDCKIMTSKTDVSSSVITSLGAIVSCYGKTKCTASNKNRGIIKTFSNGCDYV SNKGVDTVSVGNTLYCVNKQEGKSLYVKGEPIINFYDPLVFPSDEFDASISQVNEKINQSLAFIRKSDEGSGLANATAAQ QEVLEAQYAMVQHIAKGIRILEARVARGGSGGNHTTWQQWEEEIENHTGNLTLLLREAANQTHIAQRDARRI wherein: ^Italicized text corresponds to the signal peptide of RSV Fusion protein;^ Bold text is a flexible linker; and^ Underlined text corresponds to the MC2S SSM.SEQ ID NO: 21 RSV F SC9-10AY-512-CT5S Also referred to as ‘S512’ MELLILKANAITTILTAVTFCFASGQNITEEFYQSTCSAVSKGYLSALRTGWYTSVITIELSNIKENKCNGTDAKVKLIKQEL DKYKNAVTELQLLMQSTPATGSGSAICSGVAVCKVLHLEGEVNKIKSALLSTNKAVVSLSNGVSVLTFKVLDLKNYIDKQ LLPILNKQSCSISNIETVIEFQQKNNRLLEITREFSVNAGVTTPVSTYMLTNSELLSLINDMPITNDQKKLMSNNVQIVRQ QSYSIMCIIKEEVLAYVVQLPLYGVIDTPCWKLHTSPLCTTNTKEGSNICLTRTDRGWYCDNAGSVSFFPQAETCKVQS NRVFCDTMNSRTLPSEVNLCNVDIFNPKYDCKIMTSKTDVSSSVITSLGAIVSCYGKTKCTASNKNRGIIKTFSNGCDYV SNKGVDTVSVGNTLYCVNKQEGKSLYVKGEPIINFYDPLVFPSDEFDASISQVNEKINQSLAFIRKSDELGSGLANATAA QQEVLEAQYAMVQHIAKGIRILEARVARGGSGGNHTTWQQWEEEIENHTGNLTLLLREAANQTHIAQRDARRI wherein: ^Italicized text corresponds to the signal peptide of RSV Fusion protein;^ Bold text is a flexible linker; and^ Underlined text corresponds to the MC2S SSM.SEQ ID NO: 22 RSV F SC9-10AY-513-CT5S Also referred to as ‘S513’ MELLILKANAITTILTAVTFCFASGQNITEEFYQSTCSAVSKGYLSALRTGWYTSVITIELSNIKENKCNGTDAKVKLIKQEL DKYKNAVTELQLLMQSTPATGSGSAICSGVAVCKVLHLEGEVNKIKSALLSTNKAVVSLSNGVSVLTFKVLDLKNYIDKQ LLPILNKQSCSISNIETVIEFQQKNNRLLEITREFSVNAGVTTPVSTYMLTNSELLSLINDMPITNDQKKLMSNNVQIVRQ QSYSIMCIIKEEVLAYVVQLPLYGVIDTPCWKLHTSPLCTTNTKEGSNICLTRTDRGWYCDNAGSVSFFPQAETCKVQS NRVFCDTMNSRTLPSEVNLCNVDIFNPKYDCKIMTSKTDVSSSVITSLGAIVSCYGKTKCTASNKNRGIIKTFSNGCDYV SNKGVDTVSVGNTLYCVNKQEGKSLYVKGEPIINFYDPLVFPSDEFDASISQVNEKINQSLAFIRKSDELGSGLANATAA QQEVLEAQYAMVQHIAKGIRILEARVARGGSGGNHTTWQQWEEEIENHTGNLTLLLREAANQTHIAQRDARRI wherein:^ Italicized text corresponds to the signal peptide of RSV Fusion protein;^ Bold text is a flexible linker; and^ Underlined text corresponds to the MC2S SSM.SEQ ID NO: 23RSV Fusion protein DS Cav1 Foldon (McLellan et al Science 2013 doi: 10.1126 / science.1243283)Also referred to as ‘DS Cav1 Foldon’ MELLILKANAITTILTAVTFCFASGQNITEEFYQSTCSAVSKGYLSALRTGWYTSVITIELSNIKKNKCNGTDAKVKLIKQEL DKYKNAVTELQLLMQSTQATNNRARRELPRFMNYTLNNAKKTNVTLSKKRKRRFLGFLLGVGSAIASGVAVCKVLHLE GEVNKIKSALLSTNKAVVSLSNGVSVLTFKVLDLKNYIDKQLLPILNKQSCSISNIETVIEFQQKNNRLLEITREFSVNAGV TTPVSTYMLTNSELLSLINDMPITNDQKKLMSNNVQIVRQQSYSIMCIIKEEVLAYVVQLPLYGVIDTPCWKLHTSPLCT TNTKEGSNICLTRTDRGWYCDNAGSVSFFPQAETCKVQSNRVFCDTMNSLTLPSEVNLCNVDIFNPKYDCKIMTSKTD VSSSVITSLGAIVSCYGKTKCTASNKNRGIIKTFSNGCDYVSNKGVDTVSVGNTLYYVNKQEGKSLYVKGEPIINFYDPLV FPSDEFDASISQVNEKINQSLAFIRKSDELLSAIGGYIPEAPRDGQAYVRKDGEWVLLSTFLGGLVPRGSGSAWSHPQF EK wherein: ^Italicized text corresponds to the signal peptide of RSV Fusion protein;^ Bold text is a flexible linker; and^ Underlined text corresponds to Foldon SSM.SEQ ID NO: 24 RSV Fusion protein His-Tag Also referred to as ‘Fsol’ MELLILKANAITTILTAVTFCFASGQNITEEFYQSTCSAVSKGYLSALRTGWYTSVITIELSNIKKNKCNGTDAKVKLIKQEL DKYKNAVTELQLLMQSTQATNNRARRELPRFMNYTLNNAKKTNVTLSKKRKRRFLGFLLGVGSAIASGVAVSKVLHLE GEVNKIKSALLSTNKAVVSLSNGVSVLTSKVLDLKNYIDKQLLPIVNKQSCSISNIETVIEFQQKNNRLLEITREFSVNAGV TTPVSTYMLTNSELLSLINDMPITNDQKKLMSNNVQIVRQQSYSIMSIIKEEVLAYVVQLPLYGVIDTPCWKLHTSPLCT TNTKEGSNICLTRTDRGWYCDNAGSVSFFPQAETCKVQSNRVFCDTMNSLTLPSEVNLCNVDIFNPKYDCKIMTSKTD VSSSVITSLGAIVSCYGKTKCTASNKNRGIIKTFSNGCDYVSNKGVDTVSVGNTLYYVNKQEGKSLYVKGEPIINFYDPLV FPSDEFDASISQVNEKINQSLAFIRKSDELLHNVGGGGHHHHHH wherein: ^Italicized text corresponds to the signal peptide of RSV Fusion protein;^ Bold text is a flexible linker; and^ Underlined text corresponds to a His Tag.SEQ ID NO: 25 RSV Fusion protein F–T103-GS-G145—511-CT5s Also referred to as ‘VXB-211’ MELLILKANAITTILTAVTFCFASGQNITEEFYQSTCSAVSKGYLSALRTGWYTSVITIELSNIKENKCNGTDAKVKLIKQEL DKYKNAVTELQLLMQSTPATGSGSAIASGVAVSKVLHLEGEVNKIKSALLSTNKAVVSLSNGVSVLTSKVLDLKNYIDKQ LLPIVNKQSCSISNIETVIEFQQKNNRLLEITREFSVNAGVTTPVSTYMLTNSELLSLINDMPITNDQKKLMSNNVQIVRQ QSYSIMSIIKEEVLAYVVQLPLYGVIDTPCWKLHTSPLCTTNTKEGSNICLTRTDRGWYCDNAGSVSFFPQAETCKVQS NRVFCDTMNSLTLPSEVNLCNVDIFNPKYDCKIMTSKTDVSSSVITSLGAIVSCYGKTKCTASNKNRGIIKTFSNGCDYV SNKGVDTVSVGNTLYYVNKQEGKSLYVKGEPIINFYDPLVFPSDEFDASISQVNEKINQSLAFIRKSDEGSGLANATAAQ QEVLEAQYAMVQHIAKGIRILEARVARGGSGGNHTTWQQWEEEIENHTGNLTLLLREAANQTHIAQRDARRI wherein: ^Italicized text corresponds to the signal peptide of RSV Fusion protein;^ Bold text is a flexible linker; and^ Underlined text corresponds to the MC2S SSM.SEQ ID NO: 26 S508 RSV fusion protein (without signal peptide, without MC2S SSM) SGQNITEEFYQSTCSAVSKGYLSALRTGWYTSVITIELSNIKENKCNGTDAKVKLIKQELDKYKNAVTELQLLMQSTPAT GSGSAICSGVAVCKVLHLEGEVNKIKSALLSTNKAVVSLSNGVSVLTFKVLDLKNYIDKQLLPILNKQSCSISNIETVIEFQ QKNNRLLEITREFSVNAGVTTPVSTYMLTNSELLSLINDMPITNDQKKLMSNNVQIVRQQSYSIMCIIKEEVLAYVVQL PLYGVIDTPCWKLHTSPLCTTNTKEGSNICLTRTDRGWYCDNAGSVSFFPQAETCKVQSNRVFCDTMNSRTLPSEVNL CNVDIFNPKYDCKIMTSKTDVSSSVITSLGAIVSCYGKTKCTASNKNRGIIKTFSNGCDYVSNKGVDTVSVGNTLYCVNK QEGKSLYVKGEPIINFYDPLVFPSDEFDASISQVNEKINQSLAFIRK SEQ ID NO: 27 S508 RSV fusion protein (without signal peptide, with MC2S SSM; herein also referred to as VXB-213) SGQNITEEFYQSTCSAVSKGYLSALRTGWYTSVITIELSNIKENKCNGTDAKVKLIKQELDKYKNAVTELQLLMQSTPAT GSGSAICSGVAVCKVLHLEGEVNKIKSALLSTNKAVVSLSNGVSVLTFKVLDLKNYIDKQLLPILNKQSCSISNIETVIEFQ QKNNRLLEITREFSVNAGVTTPVSTYMLTNSELLSLINDMPITNDQKKLMSNNVQIVRQQSYSIMCIIKEEVLAYVVQL PLYGVIDTPCWKLHTSPLCTTNTKEGSNICLTRTDRGWYCDNAGSVSFFPQAETCKVQSNRVFCDTMNSRTLPSEVNL CNVDIFNPKYDCKIMTSKTDVSSSVITSLGAIVSCYGKTKCTASNKNRGIIKTFSNGCDYVSNKGVDTVSVGNTLYCVNK QEGKSLYVKGEPIINFYDPLVFPSDEFDASISQVNEKINQSLAFIRKGSGLANATAAQQEVLEAQYAMVQHIAKGIRILE ARVARGGSGGNHTTWQQWEEEIENHTGNLTLLLREAANQTHIAQRDARRI wherein: ^Bold text is a flexible linker; and^ Underlined text corresponds to the MC2S SSM.SEQ ID NO: 28 S508 signal peptide MELLILKANAITTILTAVTFCFA SEQ ID NO: 29 MC2S SSM – complete sequence LANATAAQQEVLEAQYAMVQHIAKGIRILEARVARGGSGGNHTTWQQWEEEIENHTGNLTLLLREAANQTHIAQRD ARRI SEQ ID NO: 30 MC2S FHRR LANATAAQQEVLEAQYAMVQHIAKGIRILEARVAR SEQ ID NO: 31 MC2S SHRR NHTTWQQWEEEIENHTGNLTLLLREAANQTHIAQRDARRI SEQ ID NO: 32 Linker GGSGG SEQ ID NO: 33 Linker GGSG SEQ ID NO: 34 Linker GSGS SEQ ID NO: 35 Linker GGGS SEQ ID NO: 36 Linker GGGGS SEQ ID NO: 37 Linker GGGGSGGGGS SEQ ID NO: 38 Linker GGGGSGGGGSGGGGS SEQ ID NO: 39 Linker GGGGSGGGGSGGGGSGGGGS SEQ ID NO: 40 Linker GGGGSG SEQ ID NO: 41 Linker GSGG SEQ ID NO: 42 Linker GSGGS SEQ ID NO: 43 Linker GSGGSG SEQ ID NO: 44 MC2 FHRR LANATAAQQEVLEAQYAMVQHIAKGIRILEARVAR SEQ ID NO: 45 MC2 SHRR NHTWQQWEEEIEQHEGNLSLLLREAALQVHIAQRDARRI SEQ ID NO: 46 MC2 SSM (non-silenced clamp) – complete sequence LANATAAQQEVLEAQYAMVQHIAKGIRILEARVARGGSGGNHTWQQWEEEIEQHEGNLSLLLREAALQVHIAQRDA RRI SEQ ID NO: 47 S508 RSV fusion protein (with signal peptide, with MC2 SSM) MELLILKANAITTILTAVTFCFASGQNITEEFYQSTCSAVSKGYLSALRTGWYTSVITIELSNIKENKCNGTDAKVKLIKQEL DKYKNAVTELQLLMQSTPATGSGSAICSGVAVCKVLHLEGEVNKIKSALLSTNKAVVSLSNGVSVLTFKVLDLKNYIDKQ LLPILNKQSCSISNIETVIEFQQKNNRLLEITREFSVNAGVTTPVSTYMLTNSELLSLINDMPITNDQKKLMSNNVQIVRQ QSYSIMCIIKEEVLAYVVQLPLYGVIDTPCWKLHTSPLCTTNTKEGSNICLTRTDRGWYCDNAGSVSFFPQAETCKVQS NRVFCDTMNSRTLPSEVNLCNVDIFNPKYDCKIMTSKTDVSSSVITSLGAIVSCYGKTKCTASNKNRGIIKTFSNGCDYV SNKGVDTVSVGNTLYCVNKQEGKSLYVKGEPIINFYDPLVFPSDEFDASISQVNEKINQSLAFIRKGSGLANATAAQQE VLEAQYAMVQHIAKGIRILEARVARGGSGGNHTWQQWEEEIEQHEGNLSLLLREAALQVHIAQRDARRI wherein: ^Italicized text corresponds to the native signal peptide of RSV Fusion protein;^ Bold text is a flexible linker; and^ Underlined text corresponds to the MC2 SSM.SEQ ID NO: 48 S508 RSV fusion protein (without signal peptide, with MC2 SSM) SGQNITEEFYQSTCSAVSKGYLSALRTGWYTSVITIELSNIKENKCNGTDAKVKLIKQELDKYKNAVTELQLLMQSTPAT GSGSAICSGVAVCKVLHLEGEVNKIKSALLSTNKAVVSLSNGVSVLTFKVLDLKNYIDKQLLPILNKQSCSISNIETVIEFQ QKNNRLLEITREFSVNAGVTTPVSTYMLTNSELLSLINDMPITNDQKKLMSNNVQIVRQQSYSIMCIIKEEVLAYVVQL PLYGVIDTPCWKLHTSPLCTTNTKEGSNICLTRTDRGWYCDNAGSVSFFPQAETCKVQSNRVFCDTMNSRTLPSEVNL CNVDIFNPKYDCKIMTSKTDVSSSVITSLGAIVSCYGKTKCTASNKNRGIIKTFSNGCDYVSNKGVDTVSVGNTLYCVNK QEGKSLYVKGEPIINFYDPLVFPSDEFDASISQVNEKINQSLAFIRKGSGLANATAAQQEVLEAQYAMVQHIAKGIRILE ARVARGGSGGNHTWQQWEEEIEQHEGNLSLLLREAALQVHIAQRDARRI wherein: ^Bold text is a flexible linker; and^ Underlined text corresponds to the MC2 SSM. SEQ ID NO: 49VXB-221 – hMPV fusion protein stabilized by the MC2S SSMLKESYLEESCSTITEGYLSVLRTGWYTNVFTLEVGDVENLTCADGPSLIKTELDLTKSALRELRTVSADQLAREEQIENPR QSRFVLGAIALGVATAAAVTAGVAIAKTIRLESEVTAIKNCLKKTNECVSTLGNGVRVLATAVRELKDFVSKNLTRAINK NKCDIPDLKMAVSFSQFNRRFLNVVRQFSDNAGITPAISLDLMTDAELARAVSNMPTSAGQIKLMLENRAMVRRKG FGILIGVYGSSVIYMVQLPIFGVIDTPCWIVKAAPSCSEKKGNYACLLREDQGWYCQNAGSTVYYPNEKDCETRGDHV FCDTAAGINVAEQSKECNINISTTNYPCKVSTGRHPISMVALSPLGALVACYKGVSCSIGSNRVGIIKQLNKGCSYITNQ DADTVTIDNTVYQLSKVEGEQHVIKGRPVSSSFDPVKFPEDQFNVALDQVFESIENSQALVDQSNRIGSGLANATAAQ QEVLEAQYAMVQHIAKGIRILEARVARGGSGGNHTTWQQWEEEIENHTGNLTLLLREAANQTHIAQRDARRI wherein: ^Bold text is a flexible linker; and^ Underlined text corresponds to the MC2S SSM. EXAMPLES Certain embodiments of the present invention are described with reference to the following examples, which are provided for the purpose of illustration only and are not intended to limit the scope of the invention. Example 1: Antigen design To determine the lead RSV F antigen, 20 antigen constructs were created (Table 3). They consisted of two different backbones native amino acid sequence from the RSV A2 strain fusion protein (SEQ ID NO:01) and the RSV F SC9-10 DSCavAY Foldon previously reported (Joyce, Zhang et al.2016) (SEQ ID NO: 02).SC9-10 DSCavAY includes a panel of structure-based mutations found to be optimal for stability and binding to pre-fusion antibodies, in particular to the monoclonal antibody AM14. Changes within SC9-10 DSCavAY (relative to the RSV A2 strain fusion protein) include: deletion of amino acids 104-144 and replacement with flexible linker GS, two inserted disulfide bridge linking amino acids 155 to 290 and 149 to 458, and site directed changes S190F, V207L, L373R. SC9-10 DSCavAY also includes the T4 fibritin, ‘Foldon’ sequence inserted at position 513. For each of the two backbones, 10 different C-terminal lengths were tested, with the MC2S sequence inserted following each amino acid between position 504 and 513 (SEQ ID NO: 03 to 22). Antigens with the backbone of the native amino acid sequence are referred to as Fwt and antigens with the SC9-10 DSCav1AY backbone are referred to as SC9-10AY. Twostabilized RSV F controls were produced; RSV Fusion protein DS Cav1 Foldon (McLellan et al. 2013) andRSV F SC9-10 DSCavAY Foldon (Joyce, Zhang et al.2016) (SEQ ID NO: 23 and SEQ ID NO: 02), and a solublenon-stabilized RSV F (SEQ ID NO: 24).

[0002] Table 3. List of RSV antigen constructs. C- SEQ Abbreviated Clamp Stabilization Full name Backbone terminal ID name linker domain length Fwt-504-CT5S F504 Wild Type1 504 GSG CT5S 03Fwt-505-CT5S F505 Wild Type1 505 GSG CT5S 04Fwt-506-CT5S F506 Wild Type1 506 GSG CT5S 05Fwt-507-CT5S F507 Wild Type1 507 GSG CT5S 06Fwt-508-CT5S F508 Wild Type1 508 GSG CT5S 07Fwt-509-CT5S F509 Wild Type1 509 GSG CT5S 08Fwt-510-CT5S F510 Wild Type1 510 GSG CT5S 09Fwt-511-CT5S F511 Wild Type1 511 GSG CT5S 10Fwt-512-CT5S F512 Wild Type1 512 GSG CT5S 11Fwt-513-CT5S F513 Wild Type1 513 GSG CT5S 12SC910AY-504-CT5S S504 SC9-10 DSCav1AY2 504 GSG CT5S 13SC910AY-505-CT5S S505 SC9-10 DSCav1AY2 505 GSG CT5S 14SC910AY-506-CT5S S506 SC9-10 DSCav1AY2 506 GSG CT5S 15SC910AY-507-CT5S S507 SC9-10 DSCav1AY2 507 GSG CT5S 16SC910AY-508-CT5S S508 SC9-10 DSCav1AY2 508 GSG CT5S 17SC910AY-509-CT5S S509 SC9-10 DSCav1AY2 509 GSG CT5S 18SC910AY-510-CT5S S510 SC9-10 DSCav1AY2 510 GSG CT5S 19SC910AY-511-CT5S S511 SC9-10 DSCav1AY2 511 GSG CT5S 20SC910AY-512-CT5S S512 SC9-10 DSCav1AY2 512 GSG CT5S 21SC910AY-513-CT5S S513 SC9-10 DSCav1AY2 513 GSG CT5S 22DSCav1-Fd DSCav DSCav13 513 N / A Foldon 23SC910DSCavAY-Fd SC910AY Fd SC9-10 DSCav1AY2 513 N / A Foldon 02RSV F Fsol Wild Type1 513 N / A N / A 241Wild type RSV-A2 subtype sequenced by the laboratory of Paul Young, University of Queensland2 Pre-fusion stabilized fusion protein (McLellan, Chen et al.2013)3 Pre-fusion stabilized fusion protein (Joyce, Zhang et al.2016)Example 2: Expression and purification The ExpiCHO-S transient expression system (ThermoFisher) was used to screen both the panel antigen constructs with at least two separate independent expressions completed. Each panel was repeated at least once. Antigens were purified by affinity chromatography with MC2S specific resin AVI-8740(Avitide / Repligen; see WO 2024 / 054656 which is incorporated herein by reference in its entirety).Antigens constructed with the SC9-10AY backbone generally had a higher titer (i.e., yield) compared to the Fwt backbone antigens and the control antigens (Figure 1). Example 3: Size exclusion chromatography Size exclusion chromatography (SEC) was conducted with the Superdex™ 200 HR analytical column (Cytiva) to determine the percentage of protein eluting within the retention volume range corresponding to the expected size for the soluble trimer (10-13 ml), compared with high molecular weight (HMW) aggregate (<10 ml) or low molecular weight (LMW) monomer (>13 ml). Either 25 or 50 µg of antigen was loaded. For the Fwt antigens, the trimer peak was less than 35% (Table 4). For the SC9-10AY antigens all the trimer peaks were also less than 35% except for S508 which was between 65-73% trimer (Table 4). Table 4. Size Exclusion Chromatography analysis of antigen panel from two independent experiments. Relative percentages calculated by AUC analysis to determine high molecular weight (HMW) protein (7-10 ml), trimer (10-13 ml) and low molecular weight (LMW) protein (13-16 ml). Expression 1 Expression 2High Low High Low Antigen Trimer Molecular Molecular Molecular Trimer % Molecular % Weight % Weight % Weight % Weight % F504 83.16 9.02 7.82 70.82 16.14 13.05F505 65.48 17.85 16.67 72.31 10.81 16.88F506 54.21 34.71 11.08 61.44 9.25 29.3F507 76.21 13.13 10.66 72.57 10.91 16.52F508 60.9 28.65 10.45 73.61 13.88 12.51F509 70.46 19.15 10.39 88.7 0 11.3F510 NA NA NA 72.85 15.89 11.25F511 73.26 12 14.74 69.36 12.84 17.8F512 76.96 11.36 11.36 68.71 12.35 18.94F513 51.41 28.83 19.76 68.98 0 32.02S504 63.6 21.1 15.2 63.6 21.2 15.2S505 81.18 9.86 8.96 69.28 25.17 5.55S506 83.27 11.26 5.46 68.17 25.27 6.56S507 66.32 29.41 4.27 64.12 31.89 3.99S508 29.96 64.54 5.49 24.91 72.59 2.5S509 67.83 0 32.17 50.13 11.84 38.03S510 65.59 29.56 7.85 53.32 28.62 17.86S511 64.27 33.41 2.31 65.91 27.27 6.82S512 64.8 3.89 31.31 NA NA NAS513 77.04 16.84 6.12 63.39 30.36 6.25 Example 4: ELISA analysis To assess the antigens ability to bind to capture antibodies in a non-conformation dependent mannerELISA was performed with pre-fusion specific monoclonal antibodies, D25 (McLellan, Chen et al. 2013),MPE8 (Corti, Bianchi et al.2013) and AM14 (Gilman, Moin et al.2015). Antigens were also compared tothe SC9-10 Fd control. Generally, the binding ability of the Fwt antigens were poor with a kD greater than 1 nM, while the majority of the SC9-10AY antigens had a kDof less than 1 nM for all three antibodies tested (Table 5). Of note there were clear differences between SC9-10AY antigens that only differed based on the C-terminal length which is linked to MC2S. Antigens S504, S507, S508, S510, S511 and S513 all showed consistent sub nanomolar binding to all 3 antibodies, whereas S505, S506, S509 and S512 did not. The reference polypeptide VXB-211 also showed poor binding for the pre-fusion specific mAb AM14. Table 5. kD for Fwt and SC9-10AY antigens from non-conformation capture ELISA. Experiment codes AY23-037B, AY23-039 and AY23-040. Cells highlighted in grey indicate that kD is below target of 1 nM. D25 MPE8 AM14 Antigen Target: kD < 1 nM Target: kD < 1 nM Target: kD < 1 nM Set 1 Set 2 Set 1 Set 2 Set 1 Set 2SC9-10AY (Control) 0.006 0.103 0.005 0.062 0.009 0.060Fwt-504-CT5s NA 3.096 NA 0.464 NA 385.200Fwt-505-CT5s NA 318.200 NA Unstable NA UnstableFwt-506-CT5s NA 327.500 NA 1142.000 NA 2284.000Fwt-507-CT5s NA 61.760 NA 0.926 NA 169.300Fwt-508-CT5s NA 4.313 NA 0.161 NA 0.957Fwt-509-CT5s NA Unstable NA Unstable NA UnstableFwt-510-CT5s NA 2.029 NA 0.184 NA 31.140Fwt-511-CT5s NA 183.300 NA 0.029 NA 131.600Fwt-512-CT5s NA 363.800 NA 4.054 NA UnstableFwt-513-CT5s NA Unstable NA Unstable NA UnstableSC910AY-504-CT5s 0.066 0.032 0.061 0.024 0.119 0.062SC910AY-505-CT5s 0.079 0.032 1.400 0.197 2668.000 9.035SC910AY-506-CT5s 0.050 0.025 0.211 0.178 8.154 4.054SC910AY-507-CT5s 0.059 0.033 0.044 0.027 0.048 0.036SC910AY-508-CT5s 0.099 0.060 0.055 0.041 0.070 0.052SC910AY-509-CT5s 7.369 0.697 402.600 Unstable Unstable UnstableSC910AY-510-CT5s 0.095 0.040 0.064 0.029 0.061 0.046SC910AY-511-CT5s 0.088 0.041 0.061 0.030 0.063 0.035SC910AY-512-CT5s 3.466 20.770 Unstable Unstable Unstable UnstableSC910AY-513-CT5s 0.030 0.045 0.050 0.054 0.053 0.055VXB-211 (control) 0.886 1.433 Unstable 0.982 Unstable Unstable Example 5: Lead MC2S stabilized RSV F antigen compared to best-in-class comparators Based on ELISA and SEC data the lead candidate S508 (SEQ ID NO: 17), obtained without signal peptide (SEQ ID NO: 27), was selected to progress into further evaluation and direct assessment relative to twobest in class comparators DS Cav1 Foldon (McLellan, Chen et al.2013) (SEQ ID NO: 23) and SC9-10 AY DSCav1 Foldon (Joyce, Zhang et al.2016) (SEQ ID NO: 2). Firstly, expression level was compared in ExpiCHO-S transient system (Figure 2). Here S508 was demonstrated to express approximately 10- and 5-fold better than the comparator antigens. Freshly expressed antigens Fsol (SEQ ID NO: 24), DS Cav1 Foldon (SEQ ID NO: 23), SC9-10 AY DS Cav1Foldon (SEQ ID NO: 2) and S508 (SEQ ID NO: 17), purified by 101F (McLellan, Chen et al. 2010)immunoaffinity chromatography were analyzed by SDS-PAGE (Figure 3), SEC (Figure 4) and ELISA (Figure 5). Antigens were then incubated at 25 and 40°C for 7 days and analysis repeated. SDS-PAGE analysis shows a single main band for each antigen at the expected MW when freshly prepared. Following incubation there is little change in S508 or Fsol at either temperature, however DS Cav1 Foldon shows the formation of some higher molecular weight bands likely due to aggregation and SC9-10AY DS Cav1 Foldon shows some proteolytic cleavage has occurred (Figure 3). SEC analysis shows aggregation present for Fsol. Lead pre-fusion stabilized antigen S508 and comparator antigens DS Cav1 Foldon and SC9-10AY Fd show majority trimer, however the percentage trimer for S508 is substantially higher with very little aggregate or LMW product present. Both DS Cav1 Foldon and SC9- 10AY DS Cav1 Foldon show an increase in aggregation following incubation at 25 or 40°C (Figure 4). ELISA analysis shows all antigens bind to MPE8 indicating this antibody is not pre-fusion specific. Fsol shows low binding for D25 and AM14 which is reduced following incubation. DS Cav1 Foldon, SC9-10AY DS Cav1 Foldon and S508 are all bound with low nanomolar kD values which are not affected by incubation at 25 or 40°C for 1 week. This is indicative that the antigens are highly stable (Figure 5). Taken together the results show clear advantage of lead MC2S-stabilized RSV F candidate S508 over the best-in-class comparators in terms of protein yield, homogeneity (i.e., trimerization) and stability. Example 6: Large scale production and comparison with licensed comparator vaccines Following the selection of S508 as the lead MC2S-stabilized RSV F candidate, large scale manufacture was completed by a contract manufacturing organization (CMO). Through selection of a stable clonal cell line and process optimization, the production yield was increased to approximately 2 g / L (Figure 6). Liquid stability of the purified drug product was also assessed with a panel of release tests including Capillary Electrophoresis (CE-SDS), SEC and potency ELISA using monoclonal antibody AM14 (Gilman,Moin et al.2015) (Figure 7). Stability analysis revealed no significant change within the antigen following 6 months incubation at 2-8°C. Similarly, incubation of S508 at 2-8°C, for 9 or 12 months did not or not substantially affect the stability of the antigen assessed by CE-SDS, SEC, and AM14 potency ELISA (Figure 11). Two RSV subunit vaccines have recently been licensed for use in humans based on strong protectiveefficacy data; Arexvy® (GSK) (Papi, Ison et al.2023) and Abrysvo® (Pfizer) (Walsh, Perez Marc et al.2023).Protein antigens were sourced from commercial suppliers for direct comparison with S508. Accelerated stability analysis in which antigens were heated for 1 h at temperatures between 25 and 70 °C and loss in reactivity to monoclonal antibodies quantified (Figure 8). In this analysis, reactivity with 101F antibody (an antibody that recognizes an epitope present on both the pre-fusion and post-fusion conformations) was unaffected, reactivity with pre-fusion specific antibodies D25, MPE8 and AM14 was reduced at elevated temperatures for both Arexvy® and Abrysvo® but remained higher for S508. Next, we directly compared the neutralizing immune response elicited in mice following vaccination with dose matched Arexvy® and S508. Groups of 8 BALB / c mice were immunized twice, three weeks apart, by intramuscular (IM) administration of either 0.5 or 3 µg antigen mixed 1:1 with AddaVaxTMadjuvant (Invivogen). Blood serum collected three weeks following the second dose was heat inactivated and the neutralization of RSV A2 strain was measured by Plaque Reduction Neutralization Titration (Figure 8). At the lower dose level of 0.5 µg of RSV antigen, S508 stimulated a strong neutralizing immune response to RSV A2 (geo mean = 5,272; 95%CI = 2,884 - 10,046), which was approximately 6-fold higher relative to the dose-matched Arexvy® antigen (geomean = 817; 95%CI = 420 - 1,710). At the higher dose level of 3 µg of the RSV antigen, monovalent S508 again stimulated a strong neutralizing immune response to RSV A2 (geomean = 6,124; 95%CI = 4,375 - 8,690), which was approximately 2-fold higher relative to the dose matched Arexvy® antigen (geomean = 2,958; 95%CI = 1,361 - 6,982). In summary the results demonstrate that S508 can be manufactured in high amounts, is compatible with long term liquid stability at 2-8°C, and was shown to elicit a stronger neutralizing immune response in a naïve mouse immunization schedule. Example 7: Immunogenicity to MC2S compared to Foldon BALB / c mice were immunised with either 0.5 or 3 µg of RSV S508 or RSVpreF3 from GSK’s RSV vaccine Arexvy, by intramuscular injection (IM) in 2 doses, 3 weeks apart, with a squalene-based oil-in-water adjuvant, AddaVax (InvivoGen). Three weeks after the second dose, serum was collected and assayed by ELISA to determine total IgG against each antigen, and the ‘tag-specific’ reactivity using an antigen containing either the MC2S domain or the foldon domain with a heterologous ectodomain (Figure 9). For RSV S508, the geometric mean of the relative response to MC2S was 7.2 and 8.1%). In comparison, for the Arexvy RSVPreF3 antigen the geometric mean of the relative response to foldon was around twice as high at 15.5 and 15.4%. Example 8: Comparison between RSV S508 and DSCavEs2 for the potential to deplete neutralising antibodies from a human plasma The ability of each antigen to deplete neutralising antibodies from a pooled human plasma sample was compared either by directly pre-incubating plasma with antigens in solution or with immobilised antigens coupled to CNBR Activated Sepharose (Invitrogen). Consistent with previous reports (Magro, Mas et al. 2012, Ngwuta, Chen et al. 2015), RSV Fsol performed poorly at removing neutralising antibodies from human plasma, whereas both DSCav1 and VXB-213, were highly efficient at depleting neutralising antibodies (Figure 10). Example 9. Phase 1 clinical trial of a vaccine comprising S508 A phase 1 randomized, placebo- and active-controlled (limited to an RSV-antigen as positive control), observer-blind, dose-finding study was conducted to evaluate the safety, reactogenicity, and immunogenicity of four dose levels of VXB-241, a bivalent vaccine comprising the herein provided S508 RSV antigen (SEQ ID NO: 27; VXB-213) and antigen VXB-221 (SEQ ID NO: 49), an hMPV fusion protein ectodomain antigen also stabilized by the silenced molecular clamp in a prefusion conformation. VXB- 241 consists of the above-mentioned antigens (i.e., VXB-213 and VXB-221) formulated in phosphate buffered saline, 0.02% polysorbate 80 without any adjuvant. The active control is the marketed RSV vaccine Arexvy (GSK), comprising 120 µg of RSVPreF3-Antigen and AS01E adjuvant. Phosphate buffered saline, 0.02% polysorbate 80 was employed as placebo. In the run-in study, a total of 16 younger adults 18 to 40 years of age (yoa), were randomised in a 1:3 ratio and received either placebo or one of four dose levels of VXB-241; 60 µg (containing 30 µg of VXB- 213 and 30 µg of VXB-221), 120 µg (containing 60 µg of VXB-213 and 60 µg of VXB-221), 240 µg (containing 120 µg of VXB-213 and 120 µg of VXB-221) or 480 µg (containing 240 µg of VXB-213 and 240 µg of VXB-221). In the main study, a total of 128 older adults 60 to 83 yoa were randomised in a 1:1:3 ratio and received either placebo, active comparator, Arexvy, or one of four dose levels of VXB-241; 60 µg (containing 30 µg of VXB-213 and 30 µg of VXB-221), 120 µg (containing 60 µg of VXB-213 and 60 µg of VXB-221), 240 µg (containing 120 µg of VXB-213 and 120 µg of VXB-221) or 480 µg (containing 240 µg of VXB-213 and 240 µg of VXB-221). On Day 1 of the run-in and the main studies, all participants had a blood sample collected and subsequently received the 1st injection of the Investigational Medicinal Product (IMP; i.e., VXB-241), Arexvy (with Arexvy only being administered in the main study), or placebo. Each younger adult in the run-in study, only received a single vaccination and were to remain in the study for ~6-7 months. Each older adult participant has received 1 injection of IMP, with a second dose to be administer at ~12 month after the first dose. These participants will remain in the study for ~24-25 months. Following IMP administration, participants of the run-in and the main studies were instructed to record any post vaccination local and systemic reactions in an electronic diary through Day 8. Reactogenicity was assessed through 10 predetermined adverse events / AEs (referred to as solicited AEs), which are known early reactions to vaccination common to many vaccines, 3 of which are local (pain, redness, swelling at the injection site, also referred to as injection site reactions), and 7 systemic (fever, headache, shivering, fatigue, myalgia, arthralgia, and gastrointestinal symptoms). Participants then returned on Day 8 forpost-dose safety assessment by assessing unsolicited AEs (see Table 7).Throughout both studies all participants had further blood draws on day 30 (1 month post vaccination) and day 182 (6 months post vaccination). Older adults in the main study, will also return to the clinic at day 364 (1 year post vaccination), although the study is ongoing, and this is yet to occur. At this time, participants will be randomised to receive either placebo or vaccination. These participants will then return for further blood draws on day 394 (1 month post booster vaccination), day 546 (6 months post booster vaccination), and day 728 (1 year post booster vaccination). An interim readout was conducted at Day 30 post vaccination at which time the primary safety andimmunogenicity endpoints were assessed as set out in Table 6.Table 6. Primary objectives and endpoints. Objective EndpointSafety. Exclude high incidence of Proportion of older adults with 1 or more unsolicited AEs in early onset unsolicited AEs in older the month after 1st IMP injection (Table 7). adults. Reactogenicity. Exclude highProportion of older adults with 1 or more solicited AEs in incidence of solicited AEs in olderthe 7 days after 1st IMP injection (Tables 8 to 10).adults. Immunogenicity. Confirm that atGeometric mean fold increase (GMFI) of RSV-A, RSV-B, least 1 dose level of VXB-241 is highly hMPV-A, and hMPV-B serum neutralizing antibody titers immunogenic 1 month after 1st IMP from pre-injection baseline (Visit 2) to ~1 month after 1st injection in older adults IMP injection (Visit 4) in older adults (Figures 12 and 13). Immunogenicity. Assess theEstimates of dose-response curves for GMFIs of RSV-A, RSV- relationship between VXB-241 dose B, hMPV-A, and hMPV-B serum neutralizing antibody titers level and neutralizing antibody from pre-injection baseline to ~1 month after 1st IMP response in older adults.injection in older adults (Figures 12 and 13).Overall vaccination with VXB-241 was safe and well tolerated. Unsolicited adverse events, also referred to as Treatment Emergent Adverse Events (TEAEs), were recorded in 58 of 128 (45.3%) older adults, with similar rates observed in participants who received placebo, Arexvy or VXB-241 (Table 7). The vast majority of TEAEs were mild or moderate in nature (Grade 1 or 2) and the majority were defined as unrelated to IMP administration upon assessment by a blinded investigator or delegate. Any solicited AEs (either local or systemic) were recorded in 59 of 128 (46.1%) older adults, with local solicited AEs recorded in 31 of 128 (24.2%) older adults and systemic solicited AEs recorded in 38 of 128 (29.7%) older adults (Tables 8-10). Local AEs were most common amongst Arexvy vaccinated participants (16 of 21; 71.4%) compared to participants who received VXB-241 (15 of 86; 17.4%) or placebo (1 of 21; 4.8%), with injection site pain the most frequent local solicitated AE. Systemic AEs were most common amongst Arexvy vaccinated participants (12 of 21; 57.1%) compared to participants who received VXB- 241 (31 of 86; 36.0%) or placebo (5 of 21; 23.8%). Fatigue, headache and muscle pain (myalgia) were the most common systemic AEs. It is likely that the increased rate of solicited AEs for Arexvy (GSK) is due to the inclusion of adjuvant AS01E compared to VXB-241, which does not include any adjuvant, as a similar result reported during the phase 1 trial of Arexvy (GSK) testing when both unadjuvanted and AS01E adjuvanted formulations were tested (Leroux-Roels et al.2022). The number of participants experiencing unsolicited AEs and solicited AEs did not increase with an increase in VXB-213 and VXB-221 antigen doses. At day 30 following IMP administration, there was no change in the RSV-A or RSV-B neutralising titre following vaccination with placebo, however following vaccination with the active control, Arexvy (GSK) the RSV-A titre and RSV-B neutralising titres increased by a geometric mean fold increase (GMFI) of 10.81 and 4.91-fold respectively (Figure 12). Vaccination with VXB-241 resulted in an increase in RSV-A and RSV-B neutralising titres at each dose level tested. At the lowest dose levels tested (60 µg) this increase was below that of Arexvy; RSV-A GMFI = 3.99 and RSV-B GMFI = 3.96. However, at higher dose (120µg, 240 µg or 480µg) the GMFI in RSV-A and RSV-B neutralising titres was similar or higher compared to Arexvy; RSV-A GMFI = 9.72, 15.06 and 11.2, and RSV-B GMFI = 5.59, 8.07 and 8.26, respectively. Of note, the VXB-241 dose level of 240 µg contains the 120 µg of RSV preF (VXB-213), which is equivalent to the dose of RSV preF with Arexvy. At this dose level the GMFI in RSV-A and RSV-B neutralising titres was roughly 50% higher compared to Arexvy (RSV-A: 15.06 vs 10.81, and RSV-B 8.07 vs 4.91). There was no change in the hMPV-A or hMPV-B neutralising titre following vaccination with either placebo or Arexvy (GSK), whereas vaccination with VXB-241 resulted in an increase in hMPV-A and hMPV-B neutralising titres at each dose level tested (Figure 13). No substantial difference in the GMFI of hMPV-A or hMPV-B, was observed between dose levels; hMPV-A GMFI = 4.49 - 7.50, and hMPV-B GMFI = 3.88 – 6.56. Of note, the VXB-241 dose level of 240 µg, which contains the 120 µg of hMPV preF (VXB-221), gave the highest GMFI in hMPV-A and hMPV-B neutralising titres. At this dose level the GMFI against RSVA, RSV-B, hMPV-A and hMPV-B were all substantially higher than that reported in a clinical trial of alternate RSV / hMPV bivalent vaccine (IVX-A12) even in comparison to adjuvanted IVX-A12, where the maximum GMFI were reported as 4-fold and 3-fold for RSV-A and RSV-B, and 5-fold and 4-fold for hMPV-A and hMPV-B (Shapiro, Sanchez-Crespo et al.2025). 

[0003] 

[0004] ReferencesBermingham et al., J Virol 2018, DOI: 10.1128 / JVI.01323-17Corti et al., Nature 2013, DOI: 10.1038 / nature12442Gilman et al., PloS Pathogens 2015, DOI: 10.1371 / journal.ppat.1005035Joyce et al., Nat Struct Mol Biol 2016, DOI: 10.1038 / nsmb.3267Leroux-Roels, et al., J Infect Dis.2022, Safety and immunogenicity of a respiratory syncytial virusprefusion F (RSVPreF3) candidate vaccine in older adults: phase I / II randomized clinical trial Magro et al. (2012). "Neutralizing antibodies against the preactive form of respiratory syncytial virus fusion protein offer unique possibilities for clinical intervention." Proc Natl Acad Sci U S A 109(8): 3089- 3094.McLellan et al., J Virol, 2010, DOI: 10.1128 / JVI.01579-10McLellan et al., Science 2013, DOI: 10.1126 / science.1243283Ngwuta et al. (2015). "Prefusion F-specific antibodies determine the magnitude of RSV neutralizing activity in human sera." Sci Transl Med 7(309): 309ra162.Papi et al., N Engl J Med 2023, DOI: 10.1056 / NEJMoa2209604Shapiro, et al., Open Forum Infect Dis 2025, Randomized Phase 1 Clinical Trial of a Respiratory SyncytialVirus and Human Metapneumovirus Combination Protein-Based Virus-like Particle Vaccine in Adults 60- 75 Years of Age.Walsh et al., N Engl J Med 2023, DOI: 10.1056 / NEJMoa2213836Each of the above-listed publications is incorporated herein by reference in its entirety.

Claims

1. CLAIMS 1. A chimeric polypeptide comprising a respiratory syncytial virus (RSV) fusion protein and a structure-stabilizing moiety, wherein said RSV fusion protein comprises an amino acid sequence having at least about 90% sequence identity to the amino acid sequence set forth in SEQ ID NO: 26, wherein said RSV fusion protein comprises a C-terminal amino acid sequence consisting of the amino acid sequence IRK or IRR, wherein said structure-stabilizing moiety comprises a first heptad repeat region (FHRR) and a second heptad repeat region (SHRR), wherein said FHRR comprises an amino acid sequence having at least about 90% sequence identity to the amino acid sequence set forth in SEQ ID NO: 30, and wherein said SHRR comprises an amino acid sequence having at least about 90% sequence identity to the amino acid sequence set forth in SEQ ID NO:

31.

2. The chimeric polypeptide according to claim 1, wherein said RSV fusion protein comprises any one or more, preferably all, of the following amino acid residues: (i) a cysteine residue in position 87 in the amino acid sequence set forth in SEQ ID NO: 26 or at a position corresponding to said position; (ii) a cysteine residue in position 93 in the amino acid sequence set forth in SEQ ID NO: 26 or at a position corresponding to said position; (iii) a phenylalanine residue in position 128 in the amino acid sequence set forth in SEQ ID NO: 26 or at a position corresponding to said position; (iv) a leucine residue in position 145 in the amino acid sequence set forth in SEQ ID NO: 26 or at a position corresponding to said position; (v) a cysteine residue in position 228 in the amino acid sequence set forth in SEQ ID NO: 26 or at a position corresponding to said position; (vi) an arginine residue in position 311 in the amino acid sequence set forth in SEQ ID NO: 26 or at a position corresponding to said position; and (vii) a cysteine residue in position 396 in the amino acid sequence set forth in SEQ ID NO: 26 or at a position corresponding to said position.

3. The chimeric polypeptide according to claim 1 or 2, wherein said RSV fusion protein comprises a C-terminal amino acid sequence consisting of the amino acid sequence IRK.

4. The chimeric polypeptide according to any one of claims 1 to 3, wherein said RSV fusion protein comprises the amino acid sequence set forth in SEQ ID NO: 26.

5. The chimeric polypeptide according to any one of claims 1 to 4, wherein said FHRR and said SHRR are linked via a linker, preferably wherein said linker is a peptide linker.

6. The chimeric polypeptide according to claim 5, wherein said linker comprises an amino acid sequence selected from GGSGG (SEQ ID NO: 32), GSG, GS, GGSG (SEQ ID NO: 33), GSGS (SEQ ID NO: 34), AS, GGGS (SEQ ID NO: 35), G4S (SEQ ID NO: 36), (G4S)2 (SEQ ID NO: 37), (G4S)3 (SEQ ID NO: 38), (G4S)4 (SEQ ID NO: 39), G4SG (SEQ ID NO: 40), GSGG (SEQ ID NO: 41), and GSGGS (SEQ ID NO: 42).

7. The chimeric polypeptide according to claim 5 or 6, wherein said linker comprises the amino acid sequence GGSGG (SEQ ID NO: 32).

8. The chimeric polypeptide according to any one of claims 1 to 7, wherein said structure-stabilizing moiety comprises an amino acid sequence having at least about 90% sequence identity to the amino acid sequence set forth in SEQ ID NO:

29.

9. The chimeric polypeptide according to claim 8, wherein said structure-stabilizing moiety comprises the amino acid sequence set forth in SEQ ID NO:

29.

10. The chimeric polypeptide according to any one of claims 1 to 9, wherein said RSV fusion protein and said structure-stabilizing moiety are linked via a linker, preferably wherein said linker is a peptide linker.

11. The chimeric polypeptide according to claim 10, wherein said linker comprises an amino acid sequence selected from GSG, GS, GGSGG (SEQ ID NO: 32), GGSG (SEQ ID NO: 33), GSGS (SEQ ID NO: 34), AS, GGGS (SEQ ID NO: 35), G4S (SEQ ID NO: 36), (G4S)2 (SEQ ID NO: 37), (G4S)3 (SEQ ID NO: 38), (G4S)4 (SEQ ID NO: 39), G4SG (SEQ ID NO: 40), GSGG (SEQ ID NO: 41), and GSGGS (SEQ ID NO: 42).

12. The chimeric polypeptide according to claim 11, wherein said linker comprises the amino acid sequence GSG.

13. The chimeric polypeptide according to any one of claims 1 to 12, wherein said chimeric polypeptide comprises an amino acid sequence having at least about 90% sequence identity to the amino acid sequence set forth in SEQ ID NO:

27.

14. The chimeric polypeptide according to any one of claims 1 to 13, wherein said chimeric polypeptide consists of the amino acid sequence set forth in SEQ ID NO: 27.

15. The chimeric polypeptide according to any one of claims 1 to 14, wherein said chimeric polypeptide further comprises an N-terminal signal peptide.

16. The chimeric polypeptide according to claim 15, wherein said signal peptide comprises (or preferably consists of) an amino acid sequence having at least about 90% sequence identity to the amino acid sequence set forth in SEQ ID NO:

28.

17. The chimeric polypeptide according to claim 15 or 16, wherein said signal peptide comprises (or preferably consists of) the amino acid sequence set forth in SEQ ID NO:

28.

18. The chimeric polypeptide according to any one of claims 15 to 17, wherein said chimeric polypeptide comprises (or preferably consists of) an amino acid sequence having at least about 90% sequence identity to the amino acid sequence set forth in SEQ ID NO:

17.

19. The chimeric polypeptide according to any one of claims 15 to 18, wherein said chimeric polypeptide consists of the amino acid sequence set forth in SEQ ID NO:

17.

20. A nucleic acid comprising a nucleic acid sequence encoding the chimeric polypeptide according to any one of claims 1 to 19.

21. The nucleic acid according to claim 20, wherein said nucleic acid is a ribonucleic acid (RNA), preferably a messenger RNA (mRNA), preferably wherein said nucleic acid encodes the chimeric polypeptide according to any one of claims 15 to 19.

22. A complex comprising three subunits, wherein each subunit is a chimeric polypeptide according to any one of claims 1 to 14.

23. A composition comprising the chimeric polypeptide according to any one of claims 1 to 14, the nucleic acid according to claim 15 or 16, or the complex according to claim 22, preferably wherein said composition is a pharmaceutical composition.

24. A kit comprising the chimeric polypeptide according to any one of claims 1 to 14, the nucleic acid according to 20 or 21, the complex according to claim 22, or the composition according to claim 23.

25. The chimeric polypeptide according to any one of claims 1 to 14, the nucleic acid according to claim 20 or 21, the complex according to claim 22, the composition according to claim 23, or the kit according to claim 24, for use in the immunization and / or the vaccination of a subject.

26. A method for the immunization and / or the vaccination of a subject, wherein the method comprises administering the chimeric polypeptide according to any one of claims 1 to 14, the nucleic acid according to claim 20 or 21, the complex according to claim 22, the composition according to claim 23, or the kit according to claim 24 to said subject.

27. Use of the chimeric polypeptide according to any one of claims 1 to 14, the nucleic acid according to claim 20 or 21, or the complex according to claim 22, in the manufacture of a medicament for the immunization and / or the vaccination of a subject.

28. The chimeric polypeptide according to any one of claims 1 to 14, the nucleic acid according to claim 20 or 21, the complex according to claim 22, the composition according to claim 23, or the kit according to claim 24, for use in the prevention of an RSV infection.

29. A method for the prevention of an RSV infection, wherein the method comprises administering the chimeric polypeptide according to any one of claims 1 to 14, the nucleic acid according to claim 20 or 21, the complex according to claim 22, the composition according to claim 23, or the kit according to claim 24, to a subject in need thereof.

30. Use of the chimeric polypeptide according to any one of claims 1 to 14, the nucleic acid according to claim 20 or 21, or the complex according to claim 22, in the manufacture of a medicament for the prevention of an RSV infection.

31. A nucleic acid vector comprising the nucleic acid according to claim 20.

32. A host cell comprising the nucleic acid according to claim 20 or 21, and / or the nucleic acid vector according to claim 31.

33. A method of production of a chimeric polypeptide, wherein the method comprises: (i) culturing the host cell according to claim 32; or (ii) expressing a chimeric polypeptide from the nucleic acid according to claim 20 or 21, and / or the nucleic acid vector according to claim 31, optionally in a cell-free transcription- translation system.

34. A method of production of an antigen-binding molecule that specifically binds to an RSV fusion protein, the method comprising:(i) immunizing an animal with the chimeric polypeptide according to any one of claims 1 to 14, or the nucleic acid according to claim 20 or 21, or the composition according to claim 23; (ii) identifying and / or isolating a B cell from the immunized animal, which specifically binds to the RSV fusion protein; and (iii) producing the antigen-binding molecule expressed by that B cell.

35. An antigen-binding molecule obtainable by the method according to claim 34.

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