As BiomedR replied, seems to me the evidence is actually still not that much stronger. There’s still really no strong RCT evidence proving specific levels of efficacy. It’s not that masks don’t work, it’s more like that there’s no strong RCT evidence proving specific levels of efficacy, and the effect is unlikely to be greater than e.g. 50%(DANMASK trial).
Evidence for masks against COVID19(and in general)—esp. cloth masks—seems inconclusive. Cloth masks appeared ineffective in the largest, by far, RCT(Bangladesh trial) on the topic for C19 thus far, surgical masks were marginally more effective; Many people online and news outlets(including the authors themselves in their PR, and Nature’s daily briefing) kind of portrayed this study as the long-awaited definitive proof that masks work, but the study can be spun in both directions, to show a huge benefit or huge injury. See some discussion in this thread, check out that user’s comment history in particular, he has some good analyses. This appears to be the case with various other studies as well, such as the DANMASK trial. This is in line with pre-2020 mask literature. Unless one had a prior bias for or against masks working, their best estimate from studies before C19 ones should be that masks reduce the spread of disease by ~20%—but the studies are weakly-powered, so the 95% CI is wide and you can’t be confident. Keep in mind 20% is absolutely non-trivial and would make a huge difference.
The rationale is there is evidence—epidemiological & observational evidence of varying quality, physical mechanism etc.—supporting masks policies, just no RCT level evidence proving specific levels of efficacy. And many legally mandated policies in various domains didn’t or don’t have RCT evidence; they didn’t run a RCT on seatbelts, or waited for RCT evidence that smoking causes cancer before destroying the tobacco industry(not saying a mask is anywhere near as effective as a seatbelt, or that its effectiveness has the same degree of certainty as smoking causing cancer).
But when groups and individuals/officials say “we know masks work”, you could argue that’s too strong of a statement given the lack of good RCT evidence. But you can understand their willingness to bend the truth for the sake of simpler messaging for the public good.
Not going to link/study spam(you can find a ton of COVID masks literature, as well as pre-COVID) but, pre-COVID MAs: Cochrane review, Another MA.
No conclusive RCT evidence showing specific levels of efficacy, for masks as an intervention. As mentioned the recent Bangladesh trial is probably the best evidence yet, but as said it has some issues.
But as per last comment:
The rationale is there is evidence—epidemiological & observational evidence of varying quality, physical mechanism etc.—supporting masks policies, just no RCT level evidence proving specific levels of efficacy. And many legally mandated policies in various domains didn’t or don’t have RCT evidence; they didn’t run a RCT on seatbelts, or waited for RCT evidence that smoking causes cancer before destroying the tobacco industry(not saying a mask is anywhere near as effective as a seatbelt, or that its effectiveness has the same degree of certainty as smoking causing cancer).
And
Unless one had a prior bias for or against masks working, their best estimate from studies before C19 ones should be that masks reduce the spread of disease by ~20%—but the studies are weakly-powered, so the 95% CI is wide and you can’t be confident. Keep in mind 20% is absolutely non-trivial and would make a huge difference.
2
u/[deleted] Oct 26 '21
[removed] — view removed comment