Objective  To understand the hemagglutinin and neuraminidase genetic variation of influenza A (H1N1) pdm09 virus in Songjiang, Shanghai, during 2017–2019.

  Methods  A total of 46 strains of influenza A (H1N1) pdm09 virus were randomly selected for hemagglutinin and neuraminidase sequencing analysis. Neuraminidase inhibition test was performed to analyze the susceptibilities of the influenza virus strains to Oseltamivir and Zanamivir.

  Results  In the strains of influenza A (H1N1) pdm09 virus, 46 belonged to 6B.1A branch. Most of the virus strains had evolved into 6B.1A2, 6B.1A5A and 6B.1A6 subclades. The homologies of HA and NA nucleotide sequences between the strains and the WHO 2019/20 vaccine strain A/Brisbane/02/2018 were 98.6%–99.4% and 99.1%–99.7% respectively. Amino acid mutations occurred in 23 loci of HA1 protein. S74R+S164T+T185I HA covariation occurred in 43.48% of the strains, indicating the antigenic drift of the influenza virus. Egg-adaptability analysis founded three amino acid changes in the HA1 gene: D187V, Q223R and E224K.25 amino acid mutations occurred in the NA protein, of which E119K NA mutation occurred in the NA enzyme active site. In neuraminidase inhibition test, all the strains were sensitive to Oseltamivir and Zanamivir.

  Conclusion  The genetic variation existed in the HA and NA gene of influenza A (H1N1) pdm09 virus. It is necessary to strengthen the genetic evolution surveillance for influenza viruses to provide the evidence for the effective prevention and control of influenza.