Analysis of antigenicity and hemagglutinin genetic characteristics of influenza A(H1N1)pdm09 virus strains isolated in Shanghai during 2018-2019 influenza surveillance year

Abstract

Objective To analyze the antigenicity, genetic characteristics and variation of the hemagglutinin(HA) protein of influenza A(H1N1)pdm09 virus circulating in Shanghai during 2018-2019 influenza surveillance year. Methods Hemagglutinin inhibition test was performed to analyze the antigenicity of eighty-four influenza A(H1N1)pdm09 virus strains isolated in Shanghai from April 2018 to March 2019. Sixty-five influenza virus strains isolated from different districts of Shanghai were sequenced and analyzed. Results Clade 6B.1 H1N1 virus was the predominant strains circulating in Shanghai. A few epidemic strains belong to the 6B.2 branch. The similarities of clade 6B.1 nucleotide sequences compared with the vaccine strain A/Michigan/45/2015 were 97.1%-98.8%. The homology with the newly recommended vaccine strain A/Brisbane/02/2018 were 97.5%-99.4%. Mainly fifteen amino acids had mutated in the HA protein sequence, and three mutations, S91R, S181T and T202I were involved in three different epitopes which indicated that the antigenic drift had occurred in the influenza virus. Conclusions The majority of influenza A(H1N1)pdm09 subtype virus strains circulating in Shanghai were well matched with the vaccine strain A/Michigan/45/2015 recommended by WHO. It is necessary to continue strengthening the surveillance on influenza virus variation to improve the efficacy of influenza vaccines. Key words: Influenza A(H1N1)pdm09; Hemagglutimin; Antigenicity; Genetic characteristics