During the European 2016/17 influenza season, A(H3N2) viruses have predominated and the majority clustered in genetic subclade 3C.2a1. Genetic analyses showed that circulating viruses have undergone considerable genetic diversification of the haemagglutinin gene from the current vaccine virus A/Hong Kong/4801/2014 (clade 3C.2a), but the antigenic data that is limited by the challenges with the antigenic charact...