Lots more research is necessary, here. Aerosols appear to be an important means of COVID-19 transmission, however the evidence still points to large droplet spread as being the predominant means of transmission. (Fomite transmission contributes also, but in minor way.) Thus, in public areas, the six foot distancing rule is an every effective for reducing transmission and should be one of our key messages, along with mask-wearing, hand washing and not touching one's face.

Regarding aerosols and droplets, we still don=E2=80™t know how many virus particles will cause an infection, but it is likely that a droplet will contain more of them than a finer particle. Further, distance, space, dispersion will all generally result in a lower probably of an infectious dose landing on your mucus membranes. Your risk will always be higher when standing within six feet from an infectious person than if standing twenty feet away.

p.s., Yale has 100,000 KN95 masks and we can=E2=80™t fit people to any of them.

p.s.s., We don't normally do spirometry as part of our respirator medical evaluations, unless the person's medical history indicates its necessity.

p.s.s.s., Re the "medical paper mask" comment, ASTM surgical masks used in hospitals are effective droplet protection and do provide some filtration. Years of evidence has proven their effectiveness in preventing disease in healthcare workers. See https://www.cebm.net/covid-19/what-is-the-efficacy-of-standard-face-masks-compared-to-respirator-masks-in-preventing-covid-type-respiratory-illnesses-in-primary-care-staff/ For infection control, these same masks are used in healthcare facility for "source control" (e.g., transporting a TB patient), which I agree is not PPE.

Pete Reinhardt, Yale EHS Director

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