A new Cochrane review of RCTs casts doubt on the effectiveness of masks in community settings for preventing COVID infection. But adherence to proper masking is often low in such settings. We don’t yet know if people who diligently mask are protected. Here’s how to find out.
What's needed is a "Challenge" RCT. The study would recruit, say, 100 healthy, vaccinated, young adults (volunteers) - i.e., people at extremely low risk of severe COVID. They would be randomly assigned to a treatment group (diligent masking) vs a control group (no masking).
All 100 individuals would then be asked to live in a dormitory for several days alongside a few people who actually have COVID. The treatment group would properly mask 100% of the time (and be monitored to ensure this); the control group & COVID patients wouldn't mask.
Everyone would watch TV together, play Pinochle, hang out, etc. The study would then measure whether the subsequent COVID infection rate is lower in the treatment vs control group. (Variations on this study design could be used to test N95 masks vs surgical masks vs no masks.)
Right now, we're all guessing as to whether - if we diligently mask in grocery stores, schools, airplanes - we're at all protected vs COVID. (Simulation studies of drop filtration thru masks are not good evidence.) An RCT like the above could provide a convincing answer.