The Incoming Influenza Season - China, the United Kingdom, and the United States, 2021-2022

Introduction: Seasonal influenza activity has declined globally since the widespread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission. There has been scarce information to understand the future dynamics of influenza - and under different hypothesis on relaxation of non pharmaceutical interventions (NPIs) in particular - after the disruptions to seasonal patterns. Methods: We collected data from public sources in China, the United Kingdom, and the United States, and forecasted the influenza dynamics in the incoming 2021-2022 season under different NPIs. We considered Northern China and Southern China separately, due to the sharp difference in the patterns of seasonal influenza. For the United Kingdom, data were collected for England only. Results: Compared to the epidemics in 2017-2019, longer and blunter influenza outbreaks could occur should NPIs be fully lifted, with percent positivity varying from 10.5 to 18.6 in the studying regions. The rebounds would be smaller if the mask wearing intervention continued or the international mobility stayed low, but sharper if the mask-wearing intervention was lifted in the middle of influenza season. Further, influenza activity could stay low under a much less stringent mask-wearing intervention coordinated with influenza vaccination. Conclusions: The results added to our understandings of future influenza dynamics after the global decline during the coronavirus disease 2019 (COVID-19) pandemic. In light of the uncertainty on the incoming circulation strains and the relatively low negative impacts of mask wearing on society, our findings suggested that wearing mask could be considered as an accompanying mitigation measure in influenza prevention and control, especially for seasons after long periods of low-exposure to influenza viruses. Seasonal influenza activity declines globally during the during the coronavirus disease 2019 (COVID-19) pandemic (1-4). For instance, in China, influenza activity, as measured by percentage of submitted specimens testing positive, dropped from 11.8% to 2.0% in 2020-2021 influenza season, compared to the past 5 years (5). The long-period of low-exposure to influenza viruses adds great uncertainty on preparedness for the incoming 2021-2022 influenza season. Influenza vaccination is one of the most effective measures in seasonal influenza prevention and control, but with only a few influenza viruses circulating, it could be difficult to determine the targeted strains for vaccination. In this context, it is of primary importance to identify alternative mitigation measures for the incoming 2021-2022 influenza season, the first season after long periods of virtually no influenza outbreaks worldwide. Using data from China, the United Kingdom, and the United States, we forecasted the influenza activity in the incoming 2021-2022 influenza season under hypothetical scenarios without non-pharmaceutical interventions (NPIs) and with different assumptions on mask-wearing and mobility levels.