CDC says community use of cloth masks helps control the spread of COVID-19
The novel coronavirus discovered in 2019 (COVID-19) is primarily transmitted by respiratory droplets generated when people cough, sneeze, sing, talk or breathe. This is why the CDC recommends community use of non-valved, multilayer cloth masks to reduce the emission of virus-laden droplets. It’s especially relevant for asymptomatic or presymptomatic infected wearers who feel well and may be unaware of their ability to infect others. These people account for more than 50 percent of transmissions, it is estimated. Face coverings also help reduce inhalation of infected droplets by the wearer. The community benefits from everyone using masks consistently and correctly.
Multilayer cloth masks block not only the release of exhaled respiratory particles into the environment, but also the microorganisms these particles carry. Cloth masks effectively block most large droplets, as well as the exhalation of fine droplets and particles (also often referred to as aerosols), which increase in number with the volume of speech. Such masks can both block up between 50-70 percent of these fine droplets and particles and limit the forward spread of those that are not captured. An 80 percent blockage has been achieved in human experiments that have measured blocking of all respiratory droplets,with cloth masks in some studies. These masks are performing on par with surgical masks as barriers.
Some studies also demonstrate that cloth masks reduce wearers’ exposure to infectious droplets. Multiple layers of cloth with higher thread counts have demonstrated superior performance compared to single layers of cloth with lower thread counts. Some materials, such as silk, have also been found to help repel moist droplets and reduce fabric wetting, thus maintaining breathability and comfort.
As COVID-19 is still a new virus, the data regarding the effectiveness of community masking are limited to observational and epidemiological studies. But a recent investigation into a highexposure event in which two symptomatically ill hair stylists interacted for an average of 15 minutes with each of 139 clients during an eight-day period found that none of the 67 clients who subsequently consented to an interview and testing developed an infection. The stylists and all clients wore masks in the salon as required by local ordinances and company policy. And a study of an outbreak aboard the aircraft carrier USS Theodore Roosevelt, an environment notable for congregate living quarters and close working environments, found that the use of face coverings onboard was associated with a 70 percent reduced risk.
Seven studies have confirmed the benefit of universal masking in community-level analyses: in a unified hospital system; a German city; a U.S. state; a panel of 15 U.S. states and Washington, D.C.; as well as both Canada and the U.S. nationally. Each analysis demonstrated that, following directives from organizational and political leadership for universal masking, new infections fell significantly. Two of these studies and an additional analysis of data from 200 countries that included the U.S. also demonstrated reductions in mortality.
Adopting universal masking policies can help avert future lockdowns, especially if combined with other non-pharmaceutical interventions such as social distancing, hand hygiene and adequate ventilation.
—Centers for Disease Control and Prevention, National Center for Immunization and Respiratory Diseases (NCIRD), Division of Viral Diseases
