Objective To examine the relationship of influenza A virus HA genetic drift and its antigenic drift with the epidemiologic situation of H3N2 circulated in Shanghai from 2010 to 2013.
Methods Real-time polymerase chain reactor was used to test the patients with influenza like illness (ILI) who visited Shanghai influenza sentinel hospitals and analyze epidemiologic characteristics of H3N2 viruses. Embryonated eggs were inoculated with virus for amplification of viral yield, and allantoic fluids from virus positive embryos were used to extract viral RNA. HA gene sequences were amplified by reverse transcription polymerase chain reaction and sequenced with ABI 3730xl. The amino acid changes were analyzed with MegAlign software and the phylogenic tree was drawn by MEGA software.
Results H3N2 subtype was the dominant influenza strain in the years of 2010, 2012, and 2013. A seasonal variation of H3N2 influenza incidence in Shanghai was recognized, which concurred with the other regions of China. The H3N2 viruses isolated in 2010 were different in amino acid sequences on HA1 domain protein molecule from the WHO vaccine strains in 2011. There were 35 amino acid substitutions, among which twenty-three positions showed significant changes and six lie in four antigen determinant regions. The phylogenic tree showed the strains isolated after 2011 belonged to a different branch.
Conclusion Antigenic drift of influenza subtype H3N2 is correlated with the influenza epidemics in Shanghai.
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