Virological characteristics of influenza A (H3N2) virus strains isolated in mainland China during 2014-2015 influenza surveillance year

Objective To analyze the antigenic and genetic variation of influenza H3N2 virus strains circulating in mainland China during 2014-2015 influenza surveillance year and to study the matching of circulating virus strains with vaccine strain for providing the guidance for the prevention and control of influenza. Methods Hemagglutinin inhibition test was performed to analyze the antigenicity of 2 516 influenza H3N2 virus strains isolated in mainland China from April 2014 to March 2015. Seventy influenza virus strains isolated from different provinces of China were sequenced and analyzed. Results Clade 3C.3a H3N2 virus was the predominant strain circulating in mainland China during 2014-2015. The clade 3C.2a virus strains were detected in October 2014. Compared with the vaccine strain A/TX/50/12, strains of the two clades showed amino acid mutations in antigenic sites A and B and receptor binding site. Results of the antigenic analysis indicated that up to 95.1% of the tested strains showed lower antigenicity to the vaccine strain A/TX/50/12 isolated from embryonated egg. Conclusion The majority of influenza H3N2 subtype virus strains circulating in the mainland China were not well matched with the vaccine strain A/TX/50/12 recommended by WHO. It is necessary to strengthen the surveillance on influenza virus, to establish a platform for the construction of influenza vaccine strains in China and to improve the efficacy of influenza vaccines. Key words: Influenza virus; Influenza A virus subtype H3N2; Antigenicity; Genetic characteristics