Whole genome evolution analysis of influenza B viruses in Sichuan province from 2014 to 2016

Objective To understand the epidemiological characteristics of influenza B virus and to analysis the matching of current circulating strains with international vaccine strains, as well as the whole genome variations of influenza B viruses prevalent in Sichuan from 2014 to 2016. Methods The genomes of 29 influenza B virus stains isolated from 2014 to 2016 in Sichuan province were sequenced and assembled. Phylogenetic analysis for each gene segment was conducted using BioEdit and MEGA 5.0 software. Results Influenza B/Yamagata lineage (BY) virus was predominant from 2014 to 2015 while influenza B/Victoria lineage (BV) virus became predominant in 2016. The whole-genome evolution analysis showed that among the 29 strains. 5 strains had inter-lineage reassortants between HA gene of BY virus and NA gene of BV virus. Compared with international vaccine strains B/Massachusetts/2/2012, the HA protein of 15 BY strains had 14 mutations at amino acid sites such as K58R, A118P, N126K, S160I, N176Y, and the mutations were mainly detected in group I branch of the phylogenetic tree. Compared with international vaccine strains B/Brisbane/60/2008, the HA protein of 11 BV strains showed two amino acid mutations at sites of I127V, N139D. No substitution was found in important enzyme active sites and neuraminidase inhibitor resistant sites of the 29 isolates strains. Conclusions Both BY and BV viruses were alternately prevalent in Sichuan from 2014 to 2016. Inter-lineage reassortants of HA/NA genes of BY/BV viruses occurred in 5 strains, causing losses of the protective effect of the vaccine. A bivalent vaccine may be better for the induction of protective immunity. The important amino acid sites on NA were relatively conservative. Key words: Influenza B virus; Genome-wide association study; Hemagglutinin; Neuraminidase; Phylogenetic analysis