Seasonal Trivalent Inactivated Influenza Vaccine Does Not Protect against Newly Emerging Variants of Influenza A (H3N2v) Virus in Ferrets

The recent increase in human cases of influenza A H3N2 variant virus A(H3N2)v highlights the need to assess whether seasonal influenza vaccination provides cross-protection against A(H3N2)v virus. Our data demonstrate that the 2011-2012 trivalent inactivated influenza vaccine (TIV) protected ferrets against homologous H3N2 virus challenge but provided minimal to no protection against A(H3N2)v virus. The complete absence of specific hemagglutination inhibition antibody response to A(H3N2)v is consistent with the poor cross-protection observed among TIV-immune animals.