Seasonal epidemiological characteristics and dynamic changes of influenza viruses subtypes/lineages in Guangdong, 2014–2020

  Objective  To explore the seasonality, epidemiological characteristics and dynamic changes of different subtypes/lineages of influenza viruses in Guangdong Province and provide evidences for precise prevention and control of influenza in Guangdong.

  Methods  Data on weekly influenza pathogen surveillance from the week 36of 2014 to the week 35 of 2020 were collected in Guangdong. The moving epidemic method (MEM) was used to determine annual epidemic period, and characteristic of seasonality were analyzed. The epidemiologic characteristics and dynamic change of different subtypes/lineages of influenza viruses were compared and analyzed with χ² test.

  Results  Influenza mainly occurred in winter, spring and summer in Guangdong. The incidence peaks mainly occurred in summer before and during 2016–2017 and in winter during and after 2017–2018. Based on data of the epidemic seasons from 2014–2015 to 2018–2019, the positive rate was lowest in age group 0–2 years, but increased with age and reached the peak in age group 7–18 years, then decreased. The distribution of the virus subtypes/lineages varied in different age groups, the proportion of influenza A virus was higher than influenza B virus. Influenza A (H1N1) pdm09 virus and influenza B virus (Yamagata lineage) were mainly detected in winter, influenza A (H3N2) virus in summer, and influenza B virus (Victoria lineage) in spring. Compared with results during before and during 2016–2017, the proportions of infections in age groups 7–18 years and 19–59 years increased, while the proportions of infections in other age groups decreased, and influenza A (H1N1) pdm09 virus and influenza B virus (Yamagata lineage) were mainly detected in winter, influenza A(H3N2) virus in spring, but influenza B virus (Victoria lineage) still in spring during and after 2017–2018.

  Conclusion  From 2017–2018 to now, the annual incidence peak of influenza all occurred in winter. Different subtypes/lineages of influenza viruses had specific epidemiological characteristics and trends. It is necessary to continue to strengthen influenza pathogen surveillance for the precise evaluation of incidence trend and control of influenza.