The coronavirus diameter is .06-.14 micrometer. It is a fairly large virus ( Ou. et al. 2020). A big question is why, from a physics point of view, a mask should be more effective against exhaled particles than inhaled ones. After all, the air a person breathes out has to get into the room somehow eventually.
What is needed is good studies of mask filtration of the relevant size particle. The studies we have don't seem satisfactory. I wouldn't believe any of the epidemiological studies, since there are too many confounding variables.
- 2009 Medpage Today article on use of masks against disease and during surgery, A very balanced article that discusses conflicting studies.
- Wired magazine had a good pro-mask article that lays out the flip-flop in recommendations and tries to justify them. Note that Ou. et al. 2020 does not in fact really say masks work, because they tested for up to .4 diameter particles and that article's main purpose is to look at how to clean masks.
- Howard et al (2021) is a big survey article, especially useful for its list of articles-- but it surveys the bad as well as the good studies. It is focussed on droplets, or aerosols defined as up to 4 micrometers, so almost everything is irrelevant for small aerosol transmission.
- Dr. Meehan strongly says that masks are useless against viruses and describes how surgeons wear special masks in high-oxygen conditions to prevent droplets even though studies hve shown masks reduce the surgeon's performance. (March 10, 2021). He is not especially an authority.
- Good op-ed on the folly of masks in the American Conservative (August 2021), including the switch from when it was Trump's vaccine to Biden's, the folly of cleaning surfaces, etc.
- New reason to carry a mask. Mr. P. asked if anyone had some string to tie off the intestines of a sheep we were butchering. Voila! Perfect length and elasticity. Carrying masks, you always have string at hand. Might replace the paper napkin for graphs, too.
- [ https://www.nature.com/articles/s41591-020-0843-2 Leung et al in Nature Medicine] did the right kind of exhalation study, but with only 17 covid patients, I don't trust their results despite claimed statistical significance.
April 28th, 2021 - BabylonBee.com.