Conclusion
Our review of the literature offers evidence in favor of widespread mask use as
source control to reduce community transmission: Nonmedical masks use
materials that obstruct particles of the necessary size; people are most
infectious in the initial period postinfection, where it is common to have few or
no symptoms (45, 46, 141); nonmedical masks have been effective in reducing
transmission of respiratory viruses; and places and time periods where mask
usage is required or widespread have shown substantially lower community
transmission.
When used in conjunction with widespread testing, contact tracing,
quarantining of anyone that may be infected, hand washing, and physical
distancing, face masks are a valuable tool to reduce community
transmission.
https://www.pnas.org/content/118/4/e2014564118