Antigenic variants of influenza B viruses isolated in Japan during the 2017-2018 and 2018-2019 influenza seasons.

Background: Here, we genetically and antigenically analyzed influenza B viruses (IBVs) isolated in Japan during the 2017-2018 and 2018-2019 influenza seasons.

Methods: A total of 68 IBVs (61 B/Yamagata/16/88-like [B/Yamagata]-lineage and 7 B/Victoria/2/87-like [B/Victoria]-lineage) were antigenically and genetically characterized by using hemagglutination inhibition (HI) assays and phylogenetic analysis, respectively. The susceptibility of IBVs to neuraminidase (NA) inhibitors was assessed by using a fluorescence-based NA inhibition assay.