Whole genomic analysis of two influenza H3N2 virus strains isolated from Qinghai, China

Background Influenza H3N2 virus has a faster evolution rate than other types of influenza viruses. This study was performed to better understand the molecular evolution of influenza H3N2 in Qinghai Province, China in 2017.Methods Complete sequences of eight gene segments of two influenza H3N2 isolates in 2017 in Qinghai Province were sequenced and analyzed by MEGA 6.06 software.Results Phylogenetic analysis showed that two Qinghai H3N2 isolates were relatively close to the 2016–2017 vaccine strain, 3C.2a-A/Hong Kong/4801/2014. In HA protein, compared with the 2015-2016 WHO recommended vaccine strain A/Switzerland/971 5293/2013, six amino acid substitutions were observed in epitopes A and B in Qinghai isolates in 2017, however, only two amino acid substitutions were observed in epitopes A and B in Qinghai isolates compared with the A/Hong Kong/4801/2014, which indicated 2016-2017 vaccine strain might have a better protection against the strains circulating in Qinghai Province in 2017 . Besides, amino acid substitution of K160T at the glycosylation site of HA and H75P in PB1-F2 in the two Qinghai isolates might affect the antibodies binding ability and the virulence of influenza virus. And there was no key amino acid substitution in the key sites of segment NA, M, NP, NS, PA and PB2.Conclusions The presence of several antigenic site mutations in Qinghai H3N2 isolates confirms the evolution of circulating H3N2 strains. Enhancing the surveillance of influenza epidemic by whole genome sequencing is important to monitor whether the selected vaccine strains are protective against the circulating strains in Qinghai Province.