Face Masks Against COVID-19: An Evidence Review

Abstract

The science around the use of masks by the general public to impede COVID-19 transmission is advancing rapidly. Policymakers need guidance on how masks should be used by the general population to combat the COVID-19 pandemic. Here,we develop an analytical framework to examine an overlooked aspect of mask usage: masks as source-control targeting egress from the wearer with benefits at the population-level, rather than as PPE used for ingress control for health-care workers with focus on individual outcomes. We consider and synthesize the relevant literature to inform multiple areas: 1) transmission characteristics of COVID-19, 2) filtering characteristics and efficacy of masks, 3) estimated population impacts of widespread community mask use, and 4) sociological considerations for policies concerning mask-wearing. A primary route of transmission of COVID-19 is likely via respiratory droplets, and is known to be transmissible from presymptomatic and asymptomatic individuals. Reducing disease spread requires two things: first, limit contacts of infected individuals via physical distancing and other measures, and second, reduce the transmission probability per contact. The preponderance of evidence indicates that mask wearing reduces the transmissibility per contact by reducing transmission of infected droplets in both laboratory and clinical contexts. Public mask wearing is most effective at reducing spread of the virus when compliance is high. The decreased transmissibility could substantially reduce the death toll and economic impact while the cost of the intervention is low. Given the current shortages of medical masks we recommend the adoption of public cloth mask wearing, as an effective form of source control for now, in conjunction with existing hygiene, distancing, and contact tracing strategies. We recommend that public officials and governments strongly encourage the use of widespread face masks in public, including the use of appropriate regulation.

Identifying airborne transmission as the dominant route for the spread of COVID-19

“…Also, there likely existed remnants of virus transmission after the implementation of regulatory measures, because of circumstances when the measures were not practical or were disobeyed and/or imperfection of the measures. Such limitations, which have been emphasized by the WHO (1), spurred on controversial views on the validity of wearing face masks to prevent the virus transmission during the pandemic (30). However, it is implausible that the limitations of mitigation measures alone contributed dominantly to the global pandemic trend, as exemplified by the success in China.…”

Understanding transmission and intervention for the COVID-19 pandemic in the United States

“…Notably, the uncertainties of face covering in protecting interhuman transmission, which have been emphasized by the WHO (World Health Organization, 2020), have resulted in intensive debates on wearing face masks to prevent inter-human transmission during the pandemic (Howard et al, 2020;Chu et al, 2020) and inconsistent recommendations by U.S. CDC and WHO (US Centers for Disease Control and Prevention, 2020; World Health Organization, 2020). Evidence for the effectiveness of face covering has been recently recognized, showing reduced emissions of respiratory droplets and aerosols when worn by infected individuals (Cheng et al, 2020) and prevented inter-human transmission (Hendrix et al, 2020;Wang et al, 2020).…”

Face masks considerably reduce COVID-19 cases in Germany

“… 11 surveys evidence on the population impacts of a widespread community mask use and stresses that “no randomized control trials on the use of masks … has been published.” The study which is “the most relevant paper” for ref. 11 is one that analyzed “exhaled breath and coughs of children and adults with acute respiratory illness” (ref. 12 , p. 676), that is, used a clinical setting.…”