Global Epidemiology of Human Infections With Variant Influenza Viruses, 1959-2021: A Descriptive Study.

The epidemiology of cases of variant viruses varied across time periods, geographical regions, and subtypes during 1959-2021. The transmissibility of different variant viruses between humans remains limited. However, given the continuous evolution of viruses and the rapidly evolving epidemiology of cases of variant viruses, improving the surveillance systems for human variant virus infections is needed worldwide.