Cross-protection against H7N9 influenza strains using a live-attenuated H7N3 virus vaccine

In 2013, avian H7N9 influenza viruses were detected infecting people in China resulting in high mortality. Influenza H7 vaccines that provide cross-protection against these new viruses are needed until specific H7N9 vaccines are ready to market. In this study, an available H7N3 cold-adapted, temperature sensitive, live attenuated influenza vaccine (LAIV) elicited protective immune responses in ferrets against H7N9 viruses. The H7N3 LAIV administered alone (by intranasal or subcutaneous administration) or in a prime-boost strategy using inactivated H7N9 virus resulted in high HAI titers and protected 100% of the animals against H7N9 challenge. Naïve ferrets passively administered immune serum from H7N3 LAIV infected animals were also protected. In contrast, recombinant HA protein or inactivated viruses did not protect ferrets against challenge and elicited lower antibody titers. Thus, the H7N3 LAIV vaccine was immunogenic in healthy seronegative ferrets and protected these ferrets against the newly emerged H7N9 avian influenza virus.