Massive Random-Controlled Trial of Face-Mask Protection against COVID-19 “Critics of mask mandates have cited the lack of relevant randomized clinical trials, which assign participants at random to either a control group or an intervention group. But the latest finding is based on a randomized trial involving nearly 350,000 people across rural Bangladesh.”
The pre-print study funded by Givewell.org, “linked surgical masks with an 11% drop in risk, [35% drop for 60+ yrs] compared with a 5% drop for cloth. That finding was reinforced by laboratory experiments whose results are summarized in the same preprint. The data show that even after 10 washes, surgical masks filter out 76% of small particles capable of airborne transmission of SARS-CoV-2, says Mushfiq Mobarak, an economist at Yale University in New Haven, Connecticut, and a co-author of the study. By contrast, the team found that 3-layered cloth masks had a filtration efficiency of only 37% before washing or use.”