Use of equine H3N8 hemagglutinin as a broadly protective influenza vaccine immunogen

Development of an efficacious universal influenza vaccines remains a long-sought goal. Current vaccines have shortfalls such as mid/low efficacy and needing yearly strain revisions to account for viral drift/shift. Horses undergo bi-annual vaccines for the H3N8 equine influenza virus, and surveillance of sera from vaccinees demonstrated very broad reactivity and neutralization to many influenza strains. Subsequently, vaccinating mice using the equine A/Kentucky/1/1991 strain or recombinant hemagglutinin (HA) induced similar broadly reactive and neutralizing antibodies to seasonal and high pathogenicity avian influenza strains. Challenge of vaccinated mice protected from lethal virus challenges across H1N1 and H3N2 strains. This protection correlated with neutralizing antibodies to the HA head, esterase, and stem regions. Vaccinated ferrets were also protected after challenge with H1N1 influenza A/07/2009 virus using whole viral or HA. These data suggest that equine H3N8 induces broad protection against multiple influenzas using a unique antigen that diverges from other universal vaccine approaches.