Here is Atul Gawande’s writing about protocols in a hospital to reduce the virus spread:
https://www.newyorker.com/science/medical-dispatch/amid-the-coronavirus-crisis-a-regimen-for-reentry
He does write about (among numerous other things) masks of various types and how much filtration of viruses both outbound (to protect others) and inbound (to protect the wearer) they provide, with references:
- "A study published in Nature last month shows that, if worn properly and with the right fit, surgical masks are effective at blocking ninety-nine per cent of the respiratory droplets expelled by people with coronaviruses or influenza viruses. The material of a double-layered cotton mask—the kind many people have been making at home—can block droplet emissions, as well." https://www.nature.com/articles/s41591-020-0843-2
- "A comparison study found that surgical masks did three times better than homemade masks at blocking outward transmission of respiratory viruses." https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7108646/
- "Don’t ditch your T-shirt mask, though. A recent, extensive review of the research from an international consortium of scientists suggests that if at least sixty per cent of the population wore masks that were just sixty-per-cent effective in blocking viral transmission—which a well-fitting, two-layer cotton mask is—the epidemic could be stopped." https://www.preprints.org/manuscript/202004.0203/v1
- "Benefit to the wearer may be limited, but it’s likely not insignificant: laboratory research has found that surgical masks reduce inhalation of respiratory-droplet-size particles by about three-quarters. Two-layer cotton masks filter about half as much on average, though a good fit can improve that considerably." https://www.medrxiv.org/content/10.1101/2020.04.17.20069567v2.full.pdf
- "There are masks specifically designed to not only protect others but also protect the wearer from infection: N95 respirators. These are masks that are designed to fit tightly around the nose and mouth, so that the air you breathe comes entirely through the mask, not around it. They use a filter material with a higher electrostatic charge that blocks at least ninety-five per cent of airborne particles as small as 0.3 microns. I protect you and I protect me."
- "There’s a more comfortable but more sinister N95—the N95 with a valve. The valve makes exhalation easier by getting rid of outward filtration: I protect me; I expose you. These masks are designed for people working in industrial settings where the protection is against dust or asbestos, not viruses."
The short form of what he claims:
Protect others: surgical or N95 (no valve) > cloth > N95 (with valve) or none
Protect wearer: N95 > surgical > cloth > none
(and surgical and cloth masks protect others better than the wearer)