Evaluation of Live Attenuated H7N3 and H7N7 Vaccine Viruses for Their Receptor Binding Preferences, Immunogenicity in Ferrets and Cross Reactivity to the Novel H7N9 Virus

Live attenuated influenza vaccine (LAIV) candidates of the H7 subtype, A/Netherlands/219/03 (H7N7, NL03 ca) and A/chicken/British Columbia/CN-6/2004 (H7N3, BC04 ca), were evaluated for their receptor binding specificity and immunogenicity in ferrets. The BC04 ca virus exhibited α2,3-SA and α2,6-SA dual receptor binding preference while the NL03 ca virus preferentially bound to α2,3-SA. Substitution of the Q226 and G228 (Q-G) by the L226 and S228 (L-S) residues in the HA improved binding to α2,6-SA for NL03 ca. The vaccine viruses with L-S retained the attenuation phenotype. NL03 L-S ca replicated more efficiently than the original NL03 ca virus in the upper respiratory tract of ferrets, and induced higher levels of humoral and cellular immune responses. Prior vaccination with seasonal LAIV reduced H7-specific antibody responses, but did not reduce the H7N7 vaccine mediated protection against a heterologous H7N3 BC04 wt virus infection in ferrets. In addition, the H7N3 and H7N7 vaccine immunized ferret sera cross reacted with the newly emerged H7N9 virus. These data, in combination with the safety data from previously conducted Phase 1 studies, suggest that these vaccines may have a role in responding to the threat posed by the H7N9 virus.