Virological characteristics of influenza B virus isolated in mainland China during 2014-2015 influenza surveillance year

Objective To analyze the epidemiological characteristics of the influenza B virus strains circulating in mainland China during 2014-2015 influenza surveillance year and to study the genetic similarity between them and the vaccine strains. Methods Hemagglutinin inhibition test was performed to analyze the antigenicity of influenza B virus strains isolated in mainland China during 2014-2015 influenza surveillance year. The nucleotide sequences of those virus strains were determined by using Sanger dideoxy sequencing. The phylogenetic trees were constructed based on the genes encoding the hemagglutinin 1 (HA1). The genetic characteristics of the influenza B virus strains were determined by comparing with the current vaccine strains. Results The influenza B virus strains accounted for 29.94% of all influenza virus strains isolated during 2014 to 2015. The influenza B virus strains belonged to Yamagata lineage were more than that belonged to Victoria lineage. Most of the Yamagata lineage virus strains were antigenically similar to the B/Massachusetts/2/2012 vaccine strain (95.1%). Only 48.3% of the prevalent virus strains were antigenically similar to the quadrivalent vaccine strain B/Brisbane/60/2008-like virus, while 100% of the strains were antigenically similar to the representative circulating strain B/Beijing-Haidian/1386/2013 in mainland China. Phylogenetic analysis showed that 19 Yamagata lineage virus strains were BY-HA/BV-NA intra-lineage reassortants. Mutations associated with drug resistance in genes encoding the neuraminidase (NA) were found in 8 Yamagata lineage strains, resulting in reduced drug sensitivity. Conclusion The WHO recommended trivalent influenza vaccine could protect from Yamagata lineage influenza B virus infection during 2014-2015 influenza surveillance year. However, the Victoria lineage influenza B virus strains were not match with the quadrivalent influenza vaccine strain. This study indicated that the antigenic and genetic characteristics of the prevalent influenza virus strains should be investigated in a timely manner for the selection of appropriate vaccine strains in China. Key words: Influenza B virus; Antigenic characteristics; Genetic characteristics