While there's no single slam-dunk study yet proving this with SARS-Cov-2 (Covid-19), there's so much mutually-reinforcing suggestive evidence that the authorita

While there's no single slam-dunk study yet proving this with SARS-Cov-2 (Covid-19), there's so much mutually-reinforcing suggestive evidence that the authoritative tone of this UCSF professor/researcher/doctor seems justified, to me. In particular, there's a lot of evidence from other similar respiratory viruses. Now also, there are patterns observed in masked-vs-unmasked Covid-19-hotspots for which the idea "masks cut initial infectious dose enough to make infections milder or totally asymptomatic" fits really well. You can watch Dr. Gandhi presenting on this topic with slides & multiple paper/incident references, during a UCSF 'Grand Rounds' a few weeks ago - here's a direct link to where her talk starts: https://youtu.be/Cio3rh6ta3w?t=1740 https://youtu.be/Cio3rh6ta3w?t=1740