Global projections of potential lives saved from COVID-19 through universal mask use

Background: Social distancing mandates have been effective at reducing the health impacts of COVID19. The ensuing economic downturns and unemployment increases have led many nations to progressively relax mandates. As COVID19 transmission and deaths rise in many low and middle-income countries (LMICs), with continuing widespread transmission elsewhere, policymakers are searching for options to reduce COVID19 mortality without reimposing strict social distancing mandates. Methods: Using a Bayesian meta-regression of 40 studies measuring the impact of mask use on respiratory viral infections, we estimated the reduction in transmission associated with the use of cloth or paper masks used in a general population setting. We used data from daily surveys conducted by Facebook, YouGov, and Premise, on the proportion of people reporting always wearing a mask outside their home for nearly all countries. We predicted deaths and infections until January 1st 2021 under a reference and universal mask use scenario using a deterministic transmission dynamics model with categories for susceptible, exposed, infected and recovered (SEIR). In the reference scenario, we assume continued easing of mandates but with action to re-impose mandates for a period of six weeks, at a level of eight daily deaths per million population. The universal mask scenario assumed scaling up of mask use to 95% over a one-week period. Findings: Use of simple masks can reduce transmission of COVID19 by 40% (95% uncertainty interval [UI] 20% to 54%). Universal mask use would lead to a reduction of 815,600 deaths (95% UI 430,600 to 1,491,000 deaths) between August 26th 2020 and January 1st 2021, the difference between the predicted 3.00 million deaths (95% UI 2.20 to 4.52 million) in the reference and 2.18 million deaths (95% UI 1.71 to 3.14 million) in the universal mask scenario over this time period. Mask use was estimated at 59.0% of people globally on August 18th, ranging from 41.9% in North Africa and the Middle East to 79.2% in Latin America and the Caribbean. The effect of universal mask use is greatest in countries such as India (158,832 fewer deaths in universal mask scenario, 95% UI 75,152 to 282,838 deaths), the United States of America (93,495 fewer deaths; 95% UI 59,329 to 150,967 deaths), and Russia (68,531 fewer deaths; 95% UI 34,249 to 145,960 deaths). Interpretation: The rising toll of the COVID19 pandemic can be substantially reduced by the universal adoption of masks. This low-cost policy, whether customary or mandated, has enormous health benefits and likely large economic benefits as well, by delaying the need for re-imposition of social distancing mandates.