Mask-Wearing During the COVID-19 Pandemic (preprint)

ABSTRACT

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 cases 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 nonpharmaceutical interventions, mobility changes, new cases of COVID-19 data and other control variables. The mask-wearing data were obtained from the Imperial College-YouGov multi-country survey of peoples personal habits before and during COVID-19. 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. Results 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. The decline in daily growth rate due to the combined effect of reported mask-wearing, reduced social mobility, and non-pharmaceutical interventions averages 28.1% (95% CI 24.2%-32%). These estimates remain robust across multiple sensitivity analyses. Conclusions 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. Even though the model controls for a large variety of variables that affect spread, and we run a number of robustness checks, it remains possible that some of the decline associated with face masks is related to confounding variables not included in the model. In summary, due to the confounding variables and the variations in the type of mask and its usage, randomized control trials of mask usage in populations are needed to determine the true effect of mask wearing on mitigating the transmission of infectious respiratory diseases.