Reduced cross-protection against influenza A(H3N2) subgroup 3C.2A and 3C.3A viruses among finnish healthcare workers vaccinated with 2013/14 seasonal influenza vaccine

Abstract

Virus strains in the seasonal influenza vaccine for the 2014/15 northern hemisphere season remained unchanged from those in 2013/14. During spring 2014, drifted influenza A(H3N2) viruses, subgroup 3C.3a, were detected in Finland; another subgroup, 3C.2a, emerged in the 2014/15 season and has predominated. We monitored antibody responses against vaccine and epidemic strains (2013/14 and 2014/15) among Finnish healthcare workers after influenza vaccination with the 2013/14 vaccine. The data suggest reduced cross- protection towards both subgroups of drifted A(H3N2) viruses.