A: Mostly others, but if we all wear them in places where maintaining an adequate distance from others is challenging, we can all potentially protect each other.
The key to understanding this is distinguishing transmission via ingress vs. egress.
For the most part, discussion of mask use early in the pandemic focused on preventing INGRESS (i.e., transmission of SARS-CoV-2 from sick individuals to health care workers by health care worker mask use). Prevention of transmission to health care workers who must be in close contact with patients and/or perform medical procedures which generate aerosols that can be readily inhaled requires personal protective equipment such as medical-grade respirator masks that can block small particles with proper fit (hence the emphasis on making sure such masks are available to this group).
Increasingly, focus has turned to preventing EGRESS (i.e., transmission of virus particles from mask wearers to the outside world) in settings where maintaining the recommended distance of 6 ft is difficult. The authors of the article below note, “The good news is that preventing transmission to others through egress is relatively easy. It’s like stopping gushing water from a hose right at the source, by turning off the faucet, compared with the difficulty of trying to catch all the drops of water after we’ve pointed the hose up and they’ve flown everywhere.”
While the peer-reviewed evidence of the effectiveness of cloth mask use remains limited, the authors reviewed the available literature on mask use and respiratory viruses concluding that, “…even a cotton mask dramatically reduces the number of virus particles emitted from our mouths—by as much as 99 percent. This reduction provides two huge benefits. Fewer virus particles mean that people have a better chance of avoiding infection, and if they are infected, the lower viral-exposure load may give them a better chance of contracting only a mild illness.”
In their review, the authors also “looked at a range of mathematical models and other research to learn what would happen if most people wore a mask in public”, stating, “Models show that if 80 percent of people wear masks that are 60 percent effective, easily achievable with cloth, we can get to an effective R0 of less than one.” and “Mask use in combination with physical distancing is even more powerful.”
Based on their review, the authors suggest that even without 100% effectiveness, use of cloth masks in settings where social distancing is challenging can help lower egress, thereby protecting those around you (and their mask use would in turn help protect you).
EDITED TO CLARIFY AUTHORS CARRIED OUT A NON PEER-REVIEWED REVIEW OF THE LITERATURE. Stay tuned for more peer-reviewed evidence!
The Real Reason to Wear a Mask from The Atlantic