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Can you help me understand the clinical significance of slowing the spread of COVID from 0.76% to 0.67% (< 0.1% absolute risk reduction) with surgical masks? It's nice to finally have a cluster RCT on masks. But even in a well-done high quality study, a statistically significant finding may not translate to clinical significance and advisable public policy? This study may show us that cloth masks don't provide benefit. But what degree of benefit are surgical masks providing (which also needs to weighed against the potential clinical and societal "costs/harm" of masks)?

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I think it's very telling the only cluster RCT is out of....Bangladesh. We certainly have the resources to conduct more relevant data to our specific situation within the United States. I think taking the whole thing a step further; what should be the endpoint purpose of masks in regard to what many would consider an endemic virus? In other words does the small benefit of slowing the spread in a cloth mask, at a time when a vast majority are either vaccinated or have natural immunity - serve any real medical purpose in light of the fact we will all encounter this virus.

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An 11.6% relative risk reduction for surgical masks isn't terribly compelling. There were a lot of covid like symptoms in both arms (surgical mask and no mask) of the trial with only an one (1) percent absolute risk reduction. So surgical masks aren't that great either....unless, I guess you don't know the difference between a rRR and an aRR.

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If their trial does not help us estimate their effect size, can you really say "surgical masks slowed the spread of symptomatic SARS-CoV2?"

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Figure 3 in https://www.poverty-action.org/sites/default/files/publications/Mask_RCT____Symptomatic_Seropositivity_083121.pdf shows surgical masks providing significant infection reduction for 50 years and older but none for younger age brackets. This step function seems counter-intuitive to me. Shouldn't younger people, who naturally interact more in society, benefit more from higher quality NPI?

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What I want to know is what kind of cloth masks they used in the study. Surgical masks are all similar; cloth masks aren't. You go from single layer bandannas to multi layer cloth masks with a non-woven layer and even a pocket for an additional high end filter. And cloth masks can fit much better since sizing is easier. This study only shows that the cloth masks they used and anything lower quality are less effective. If they did the study with high grade 4 layer masks, well and good, cloth masks don't work. But if they did it with lower grade masks then my high end cloth masks might still work.

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The observed "better" results for surgical masks could still be an indirect effect (in general, the study observed increased "distancing" in intervention villages; it could just be that surgical masks turned more people into hypochondriacs). Such an indirect, psychologically-derived impact would not translate to other cultures or economic contexts.

The results for elderly villagers in the surgical mask villages are especially spurious. How many people are actually over 60 years-old in rural Bangladesh? It seems like less than 10% of the population. Less than .1 of the population of 200 (surgical mask intervention) villages is too small for the statistical confidence the authors asserted.

Note that the study observation period wasn't even during a wave. They only collected blood samples from villagers who reported "symptoms" during household surveys, and there was no baseline seropositivity sampling, contra the author's own distorted text (it seems that "baseline" simply refers to seropositivity in week 1 survey respondents; but it's unclear).

And as commented by Hannah, to what end? What is the point of slowing transmission? It is a seasonal virus.

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Thoughts on higher quality masks? It seems to make sense to only compare cloth to surgical when that was all that was available but if it’s now easier to get a KN95 or N95 should we evaluate those? And if they’re highly effective, and available, why not push for them? Sure, not everyone may want to wear an N95, but some of the KN95s are more comfortable and if the point is to actually limit spread…

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Just another dude on the internet too much. but I'm beginning to go from a pro-mask stance to a perhaps we don't need them for kids < 12 stance. But with some of the anit-mask stuff I've seen, I think it misses a key point about what we know. Enclosed spaces lend themselves to a certain viral load gathering in the air. The fact the virus can slip through a mask doesn't address the rate at which an enclosed space becomes more infectious. As such, I still think promoting masks in such cases makes sense. In my head, adult lungs are potential pumps of transmission dense air in enclosed spaces. But children < 12, or vaccinated adults...perhaps that drops. Curious how others see it.

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Poor trial design, poor control, no baseline. It simply proves people are gullible. https://mail.google.com/mail/u/0/?tab=rm#search/bangla/WhctKKWxdNWvjjzQFwxMlPPNBbVDffJPFLxdGVgxfXJdHTLcVVxpFwzcmcCxdLcGzsDCqXB

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