Influenza’s plummeting and future dynamics: the roles of mask wearing, mobility change and SARS-CoV-2 interference (preprint)

Untangling lessons from the influenza’s plummeting during the COVID-19 pandemic is critical for mitigating seasonal and pandemic influenza. Here we explored a country-specific inference model to estimate the effects of mask-wearing, mobility changes (international and domestic) and SARS-CoV-2 interference in China, England and the United States. We found that mask wearing had a larger reduction than mobility changes in all the regions. Only in 2019-2020, SARS-CoV-2 interference had an observable effect, with values varying at the timing of the influenza season and the speed of SARS-CoV-2 community transmission. Compared to the epidemics in 2017–2019, longer and blunter rebounds could occur in the incoming 2021–2022 season, but the rebound would be smaller if less stringent mask mandates continued or the international mobility stayed low. Our results bear implications for understanding how influenza evolves under non-pharmaceutical interventions and other respiratory diseases, and will inform designing of tailored public health measures.

The Effects of Mask Wearing, Mobility Change and SARS-CoV-2 Interference on Seasonal Influenza in Northern China, Southern China, England, and the United States (preprint)

Background: Seasonal influenza activity typically peaks in winter months but plummets globally during the COVID-19 pandemic. Untangling lessons from the influenza’s unprecedented low profile is critical for informing preparedness for incoming influenza seasons.Methods: We collect data from public sources in Northern China, Southern China, England and the United States. We estimate the individual effects of mask-wearing, mobility change (international and domestic) and SARS-CoV-2 interference, and forecast the influenza activity in the incoming 2021–2022 influenza season, using a country-specific inference model.Findings: The one-week increase of the mask-wearing intervention has a percent reduction of 11·3% to 35·2% on influenza activity in the four regions. The one-week mobility mitigation has smaller effects, 1·7% to 6·5% for the international and 1·6% to 2·8% for the domestic. In 2020–2021, the mask-wearing intervention alone could decline 13·3 to 19·8 percent positivity. The mobility change alone could reduce 5·2 to 14·0 percent positivity, of which 79·8% to 98·2% are attributed to the deflected international travel. Only in 2019–2020, SARS-CoV-2 interference has statical significant effects, and in Northern China and England only, reducing 7·6 (2·4 to 14·4) and 10·2 (7·2 to 13·6) percent positivity respectively. Compared to the epidemics in 2017–2019, longer and blunter rebounds could occur in the incoming 2021–2022 season should the mask-wearing be lifted, but the rebound would be smaller if the international mobility stayed low.Interpretation: Mask-wearing is more effective than mobility mitigation in all the four regions, although the relative advantage depends on the timing and duration of the interventions. Effects of SARS-CoV-2 interference vary at the timing of the influenza season and the speed of SARS-CoV-2 community transmission. The results improve our understandings of nonpharmaceutical interventions and other respiratory disease on influenza, and will inform the tailored public health measures for mitigating seasonal influenza and future pandemics.Funding: National Natural Science Foundation, Chinese Academy of Medical Sciences & Peking Union Medical College, and the Bill & Melinda Gates FoundationDeclaration of Interest: The authors declare no competing interests.