The global region-specific epidemiologic characteristics of influenza: World Health Organization FluNet data from 1996 to 2021.

ABSTRACT

OBJECTIVES: This study aimed to investigate region-specific epidemiologic characteristics of influenza and influenza transmission zones (ITZs). METHODS: Weekly influenza surveillance data of 156 countries from 1996 to 2021 were obtained using FluNet. Joinpoint regression was used to describe global influenza virus trends, and clustering analyses were used to classify the ITZs. RESULTS: The global median average positive rate for total influenza virus was 16.19% (interquartile range 11.62-25.70%). Overall, three major subtypes (influenza H1, H3, and B viruses) showed alternating epidemics. Notably, the proportion of influenza B viruses increased significantly from July 2020 to June 2021, reaching 62.66%. The primary peaks of influenza virus circulation in the north were earlier than those in the south. Global influenza virus circulation was significantly characterized by seven ITZs, including "Northern America" (primary peak week 10), "Eastern & Southern-Asia" (primary peak week 10), "Europe" (primary peak week 11), "Asia-Europe" (primary peak week 12), "Southern-America" (primary peak week 30), "Oceania-Melanesia-Polynesia" (primary peak week 39), and "Africa" (primary peak week 46). CONCLUSION: Global influenza virus circulation was significantly characterized by seven ITZs that could be applied to influenza surveillance and warning.