Objective  To understand the antigenicity and genetic characteristics of influenza B/Victoria (Bv) virus circulating in Guangxi between 2020 and 2021.

  Methods  36 strains of influenza Bv virus between 2020 and 2021 in Guangxi were selected for whole genome sequencing, the hemagglutinin (HA) and neuraminidase (NA) genes were assembled and analyzed. At the same time,antigenicity was analyzed by hemagglutination inhibition test.

  Results  Compared with influenza vaccine strain B/Washington/02/2019, HA and NA genes of influenza Bv virus strains between 2020 and 2021 shared 99.1%−100.0% and 99.1%–99.9% homology, respectively. Phylogenetic tree analysis found that 36 strains of influenza Bv virus all belong to the1A(∆3)B branch, which the same branch with the vaccine strain. But the Guangxi virus strains were further divided into two small branches. Antigenicity analysis showed that the two small branches were not significantly different, and both were similar to the vaccine strains. Analysis of amino acid variation sites revealed that HA protein of the strains carried amino acid mutations of R133G, N150K, and N197D, and the variation involved three antigenic determinants. Neither the active site nor the neuraminidase inhibitor resistance site of NA protein had mutations.

  Conclusion  The influenza Bv virus circulating in Guangxi between 2020 and 2021 matched the composition of the vaccine strain recommended by World Health Organization for the NorthernHemisphere. However, there is persistent variation , and it is still necessary to strengthen the surveillance of influenza virus variation to provide a scientific basis for prevention and control of influenza.