West Nile virus (WNV) is a neurovirulent mosquito-borne flavivirus. High WNV virulence was mainly associated with lineage 1 strains, but recent outbreaks have unveiled circulation of highly virulent lineage 2 strains. Co-expression of flavivirus prM and E glycoproteins drives the assembly of recombinant subviral particles (RSPs) that share antigenic features with virions. Mouse immunization with lineage 1 WNV RSPs induced a potent humoral response against WNV with production of neutralizing antibodies. A single inoculation of RSPs formulated with Al(OH)3 as adjuvant protected mice against a lethal challenge with WNV strains from lineage 1 or 2. The cross-reactivity of the response elicited by these RSPs was analyzed against the related flavivirus Usutu virus (USUV), which shares multiple ecological and antigenic features with WNV. Immunization with WNV-RSPs increased specific, although low, antibody titers found upon subsequent USUV infection.

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Development of safe, cost-effective vaccines is a desirable goal in practically all areas of human and animal health. In the latter field, foot-and-mouth disease (FMD) is paradigmatic of the challenge of designing strategies alternative to the conventional vaccines still used to prevent this highly transmissible, devastating livestock disease (Grubman & Baxt, 2004). Classical FMD vaccines rely on chemically inactivated FMD virus (FMDV) administered with an adjuvant and require about 7 days to induce a protective immunity that requires re-vaccination after 6-12 months to maintain its protective effect (Doel, 2005; Rodriguez & Grubman, 2009). High levels of circulating neutralizing antibodies are considered as the main correlate for FMDV protection, albeit this relationship is not absolute and differences in resistance to virus challenge can be found in animals with similar levels of neutralizing antibodies (McCullough et al., 1992). Duration of the protective immunity is essential in establishing the fitness of any FMD vaccine (Smitsaart & Bergmann, 2017), and boosting at approximately 6 monthly intervals is often required to maintain a protective response in pigs (Cox,