Objective: To compare the characterization of hemagglutination and the sequence of HA1 region of the influenza A (H3N2) virus in Zhejiang province and Japan in recent years.
Methods: Hemagglutinin antigenic analysis of influenza A (H3N2) viruses which were isolated in Zhejiang province was carried out and to compare their characterization of hemagglutination and the sequence of amino acids in HA1 region with the virus strains from Japan during the same period.
Results: The antigenicity and the amino acid sequence in HA1 region of the virus strains prevalent in Zhejiang in recent years have changed to some extent. Most of the virus strains were lack of hemagglutination reaction to chicken red blood cell and became "O" phase virus strains. The amino acid sequence of HA1 region of the virus strains exhibited only 94.82% of its homology with that of A/Wuhan/359/95 strain. The virus strains of Japan in the same period showed similar characteristics.
Conclusion: HA1 gene variation of influenza A (H3N2) viruses was the main cause leading to the spread of influenza in the last years.