Antigenic mapping of H2 influenza viruses recognized by ferret and human sera and predicting antigenically significant sites.

Influenza viruses cause hundreds of thousands of infections globally every year. In the past century, seasonal influenza viruses have included H1N1, H2N2, and H3N2 strains. H2N2 influenza viruses circulated in the human population between 1957 and 1968. Previously, our group demonstrated a lack of H2N2 influenza virus immunity in individuals born after 1968, as well as the effectiveness of hemagglutinin (HA)-based vaccines for multiple influenza virus subtypes. In this study, H2 antigenic maps and radial graphs were generated using previously published data from H2 HA vaccinations of ferrets and seasonal influenza vaccinations of humans. The antigenic maps revealed a stark difference in the clustering of HA antigens between ferrets and humans, and the radial graphs showed that specific antigen recognition varies greatly among different influenza preimmune ferrets. These maps also revealed the significant impact that different pre-existing immunities have on antigenic recognition and clustering of antigens after vaccine boost. From these data, we predicted two possible antigenically significant sites containing various mutations that have not been previously reported, and showed that one of these sites is relevant using mouse antisera.IMPORTANCEH2N2 influenza viruses have caused at least one known pandemic in humans, and are poised to cause future pandemics. Investigating the antigenic diversity of H2 hemagglutinin (HA) proteins provides valuable data for designing and understanding the performance of current and future vaccines. Data evaluating the differences in antigen recognition across differing pre-existing immunity can be used to predict antigenically significant sites and evaluate the impact of H1 and H3 infection and immune imprinting on H2 vaccine immunogenicity. This information can direct future studies when both extrapolating animal data to human studies and creating next-generation vaccines. Contrasting the relationships among new, contemporary, and ancestral H2 HA antigens by antigenic cartography is imperative for identifying new variants of concern and updating vaccine formulations.