Mask-Wearing During the COVID-19 Pandemic

Background: Masks have been widely recommended as a precaution against COVID-19 transmission. Several studies have shown the efficacy of masks at curbing droplet dispersion in lab settings. Using individual response data from the Imperial College London — YouGov personal measures survey, this study investigates reported mask use and its association with the spread of COVID-19.Methods: We examine the association of reported mask-wearing in a population within a country with the growth rate of active COVID-19 cases. The analysis uses country-wide data from weekly surveys of individuals’ mask-wearing behavior in public places, as well as other concurrently implemented non-pharmaceutical interventions (NPIs), mobility changes, new cases of COVID-19 data and other control variables. Because mask-wearing showed substantial variation across countries and over time, we use a reduced form econometric model to relate population-wide changes in mask-wearing to the growth rate in COVID-19.Findings: The results indicate that reported mask-wearing could play an important role in mitigating the growth of COVID-19. Widespread mask-wearing within a country associates with an expected 7% (95% CI: 3.94% — 9.99%) decline in the growth rate of daily active cases of COVID-19 in the country. This daily decline equates to an expected 88.5% drop in the growth of daily active cases over a 30-day period when compared to zero percent mask-wearing, all else held equal. These estimates remain robust across multiple sensitivity analyses and counterfactuals. Taken together with mobility changes and NPIs, the combined association of individual and institutional measures on the decline in the daily growth of COVID-19 is 28.1% (95% CI: 24.2%-32%).Interpretation: Face mask usage as a preventative measure against the transmission of COVID-19 varies widely across countries. This observational study uses data from 24 countries and finds that reported face mask usage associates with a decline in new COVID-19 cases.Funding: No external funding.Declaration of Interests: The authors have no conflict of interest.