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One thing this crisis will have taught me is that many doctors, including those who work in academic medicine, are spectacularly dumb. https://www.nejm.org/doi/full/10.1056/NEJMp2006372
Imagine being so stupid that you don't understand that, even if masks only lower the probability of infection a little bit at the individual-level, they could have a huge effect at the population-level by reducing the reproduction rate.
Of course, that's when you accept their premise, but you shouldn't. In the case of the flu, the relation between probability of infection and initial viral load is approximately linear at low doses, but sure masks that block ~80% of droplets don't work 
https://onlinelibrary.wiley.com/doi/full/10.1111/j.1539-6924.2010.01428.x
https://onlinelibrary.wiley.com/doi/full/10.1111/j.1539-6924.2010.01428.x
They also block aerosols, though much less effectively except for N95/FFP2 respirators, but again even a bit of protection could matter a great deal at the population-level and there is evidence droplets play a larger role in transmission of COVID-19. https://medium.com/@Cancerwarrior/covid-19-why-we-should-all-wear-masks-there-is-new-scientific-rationale-280e08ceee71
Anyway, this dumb propaganda is really driving me crazy, so I plan to write the mother of all "actually masks do work (even if we don't know how much the effect is exactly)" articles next week. It will be in French, but maybe I'll translate it in English.
