A new rapid expert consultation from a standing committee of the National Academies of Sciences, Engineering, and Medicine responds to questions from the White House Office of Science and Technology Policy (OSTP) regarding the effectiveness of homemade fabric masks to protect others from the viral spread of COVID-19 from potentially contagious asymptomatic or presymptomatic individuals. The rapid expert consultation does not apply to either N95 respirators or medical masks.
Overall, the available evidence is inconclusive about the degree to which homemade fabric masks may suppress spread of COVID-19 from the wearer to others. There are no studies of individuals wearing homemade fabric masks, in the course of their typical activities. Only limited, indirect evidence exists regarding the effectiveness of these masks for protecting others, when made and worn by the general public on a regular basis, the rapid expert consultation says. That evidence comes primarily from laboratory studies testing the effectiveness of different materials at capturing particles of different sizes.
The evidence from these laboratory studies suggests that while fabric masks may reduce the transmission of larger respiratory droplets, there is little evidence regarding transmission of small aerosolized particulates of the size potentially exhaled by asymptomatic or presymptomatic individuals with COVID-19. The extent of any protection will depend on how the masks are made and used, and on how mask use affects other behaviors to reduce the spread of COVID-19. Any discussion of homemade fabric masks should reinforce the central importance of physical distancing and personal hygiene, such as frequent hand-washing, in reducing spread of infection, the rapid expert consultation says.
Research that assesses the effectiveness of homemade fabric masks could provide the public with instructions on how to make, fit, use, and clean homemade fabric masks; estimates of the protection that they afford users and others and in different environments; and effective reinforcement of other precautionary behaviors.
The National Academies Standing Committee on Emerging Infectious Diseases and 21st Century Health Threats, assembled in early March at the request of OSTP and the U.S. Department of Health and Human Services’ Office of the Assistant Secretary for Preparedness and Response in response to the COVID-19 outbreak, has been providing rapid expert consultations on several topics, such as social distancing, severe illness in young adults, and crisis standards of care.
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