Virological characteristics of influenza B virus isolated in Anhui province during 2017—2018 surveillance year

Objective To analyze the epidemiological characteristics and the pathogenic features of the influenza B virus strains circulating in Anhui province during 2017-2018 influenza surveillance year. Methods The antigenic characteristics of influenza B virus was analyzed with reference ferret anti-sera. The hemagglutinin (HA) and neuraminidase (NA) genes of influenza B viruses isolated in Anhui during this period were obtained by Sanger dideoxy sequencing. Then the phylogenetic trees and amino acid mutations were analyzed respectively. Results During 2017-2018 influenza season, the activity of B Yamagata lineage virus were stronger than B Victoria lineage virus. Most of B Yamagata lineage viruses had close antigenic relation with the vaccine strain B/Phuket/3073/2013(93.3%), but D196 N substitution was detected on HA protein in all of Yamagata lineage viruses. All of B Victoria lineage viruses had close antigenic relation with the vaccine strain B/Brisbane/60/2008(100%), meanwhile I117 V and N129D were found on HA protein. Phylogenetic analysis on B influenza viruses indicated that Yamagata clade 3 and Victoria clade 1A were predominant strains, however we found that two strains had intra-clade reassortants between HA and NA gene. The NA gene of all strains did not find a molecular mutation that was less sensitive to neuraminidase. Conclusions The WHO recommended influenza vaccine could protect from influenza B virus isolated from Anhui province. However, it is still necessary to pay close attention to its significant epitope variation in order to update the vaccine candidates in time. Key words: Influenza B virus; Antigenic characteristics; Genetic characteristics