From the study:

>The intervention increased proper mask-wearing from 13.3% in control villages (N=806,547 observations) to 42.3% in treatment villages (N=797,715 observations)... Physical distancing increased from 24.1% in control villages to 29.2% in treatment villages

Mask wearing increased 218% while distancing increased by 21%. I agree this is not proof specifically about masks, the study is about specific public policy programs and not mask wearing in general, but it certainly seems like masks wearing is the biggest contributor to the reduction seen.

> Mask wearing increased 218% while distancing increased by 21%.

You can't just compare "percentage change" of two wildly different things, and leap to the conclusion that the magnitude of change is causal. It begs the entire question: if physical distancing works well, and mask wearing does not work, you could increase mask wearing by whatever percentage you like, and a smaller change in physical distancing would still overwhelm it. We don't know.

But aside from that, you skipped over an important part of what I said: distancing was higher in the surgical mask group. See Table 2.

> It begs the entire question: if physical distancing works well, and mask wearing does not work (...)

There's nothing in the study remotely suggesting that masks have no effect. Instead the study shows that mask wearing combined with other factors have a clear and unquestionable correlation with reduce Covid spread.

Even if you wish to nitpick the contribution of mask wearing in the reduction in Covid spread, it makes absolutely no sense at all to jump to the conclusion that surgical masks have no impact in spreading airborne pathogens as that's precisely what surgical masks do and the whole reason why they are extensively used by the medical community for decades.

> Instead the study shows that mask wearing combined with other factors have a clear and unquestionable correlation with reduce Covid spread.

The study shows that cloth masks (combined with other factors) have no effect on seroprevalence. It shows that surgical masks (combined with other factors) has a small-but-significant effect on seroprevalence. The confidence interval on the surgical mask group overlaps zero, so you can't rule out "no effect". At these small effect sizes, you also can't rule out the role of confounders -- it's possible that behavior change could explain all of it.

In short, neither result is "clear and unquestionable". An accurate description of the results are that they are "weak and debatable".

> The study shows that cloth masks (combined with other factors) have no effect on seroprevalence.

No, not really. If you happen to take a few minutes to read the paper, you'll notice that the study was conducted with a type of cloth mask produced locally which had a filtration efficiency rate of around 37% with a standard deviation of 6%, compared with the surgical mask's filtration efficiency of 95%.

The study also points out that the filtration efficiency of surgical masks washed 10 times with soap was 76%, and that they evaluated a type of cloth mask which can achieve a filtration efficiency of 60%.

Thus, what the study actually states is that they observed that wearing poor quality cloth masks showed high-variance results whose confidence interval includes the point estimate for surgical masks.

In other words, the study actually pointed out that using a specific type of cloth mask produced locally and which was known to have poor filtering efficiency had an effect that lies somewhere between being as good as surgical masks and not wearing anything at all.

> The confidence interval on the surgical mask group overlaps zero, so you can't rule out "no effect".

No, not really. That's not how confidence intervals work. At most, the only conclusion you can objectively draw from the data is that even though the positive effect of wearing surgical masks in the past study is clear and beyond doubt, further studies would be required to increase the resolution of that estimate.

In fact, if you happen to read the study you'll notice that the conclution states quite clearly that "We found clear evidence that surgical masks are effective in reducing symptomatic seropreva- lence of SARS-CoV-2; while cloth masks clearly reduce symptoms, we cannot reject that they have zero or only a small impact on symptomatic SARS-CoV-2 infections (perhaps reducing symptoms of other respiratory diseases)."

Also, your comments feel like a mix of moving the goalpost combined with a considerable amount of cherry-picking. It's a widely known fact that the whole point of wearing masks is primarily to reduce the viral load emitted by the wearer, and a minor benefit is to reduce our own exposure to the virus. Thus I feel that you're trying to misrepresent the whole point of wearing masks by trying to frame it as a "seroprevalence" issue. That was never, at any point in time, the reason why we have the social obligation to wear face masks and respect social distancing.

> If you happen to take a few minutes to read the paper, you'll notice that the study was conducted with a type of cloth mask produced locally which had a filtration efficiency rate of around 37% with a standard deviation of 6%, compared with the surgical mask's filtration efficiency of 95%.

I read it, thanks. The mask they used was much better than what most people are wearing:

> The cloth mask had an exterior layer of 100% non-woven polypropylene (70 grams/square meter [gsm]), two interior layers of 60% cotton / 40% polyester interlocking knit (190 gsm), an elastic loop that goes around the head above and below the ears, and a nose bridge

If a cloth mask with three layers of different materials and a nose bridge is dramatically less efficient than a simple surgical mask, then that's pretty damning for the whole idea of a cloth mask, in general.

> I read it, thanks. The mask they used was much better than what most people are wearing.

Can you give a citation for that? I think you might be in a strange place. Here nearly everybody wears surgical masks, most people were 2 : a surgical and cloth mask.

Also I'm interested in an experimental design or study design you would find acceptable. I saw your comments now on 3 papers showing evidence for mask wearing. It seems you are moving goal posts ever time.

I think it's also important to note that there was no change in physical distancing seen in indoor environments (mosques) - maybe due to the fact that it's obviously easier to spread out when outdoors. I think we are fairly confident by now that the vast majority of spread occurs indoors [1].

[1] https://academic.oup.com/jid/article/223/4/550/6009483

yes, distancing does most of the work in most common situations. a mask can only work when conversing closely for a time indoors. otherwise masks do nothing, no matter the filtration rate of the mask, because there's nothing to filter in the first place. distancing is a more universal and sensible mitigation (we're distanced from nearly all of the world population all the time).

this is why mask mandates, as currently constructed, are misguided and ignorant at best. the mandate should be to wear a mask when you're intimately sharing air (within ~3ft/1m) with another person indoors. the reason we don't have that sort of mandate is because it would mean we'd have to wear them around friends and family rather than those gross strangers who are out to kill us with their ignorance and malice (they're not).

this is also why the current mandates for restaurants (and most retail) makes no sense, as we're only going to be intimately sharing air with our friends and family in those places anyway.

Aren't you sharing air with others in any common indoors space?

I thought that was the whole aerosols debate that's basically settled by now, i.e. virus can stay suspending in the air for extended periods. With the Delta variant's characteristics this is also a much bigger problem (i.e. the same indoor space that might have been ok is no longer ok).

There were early studies with the less infectious variants that showed how people situated far from each other in indoors spaces infect each other.

So the mandate for masking in any common indoor space seems to make a lot of sense.

no, it's not "settled science" like that. the virus must traverse a gauntlet of death before reaching your juicy mucus membranes, including dessication and all manner of external forces that will inactivate it in the meantime. it falls apart in droves outside the body. you need constant exposure to warm, moist, infected exhaust so that the virus has trillions of chances of taking hold in your respiratory system, and it likely takes millions of virus particles making it across for enough to survive the immune response gauntlet inside the body. that a few virus particles in controlled tests miraculously manage to exist for a few minutes in the air has no bearing on real-world transmission rates.

that's why a mask can work (better than distancing) in that one particular situation, but distancing is a better general mitigation.

by the way, those early "studies" on long indoor spread were conjecture-based (e.g., using models), not rigorous science, and have failed to replicate.

I'm not talking about model studies. I am talking about case studies, like: https://www.nytimes.com/2020/04/20/health/airflow-coronaviru...

Also: https://www.the-scientist.com/news-opinion/ferret-study-rein...

Even early on with the Diamond Princess you've seen wide spread of the virus despite passengers being largely confined to their cabins. There were multiple other examples.

We also know the Delta variant is more infectious.

I'm not saying distancing doesn't work. Even if you assume the virus is spread in the indoors air it's not a terrible bad assumptions to think that a person emitting virus continuously will have a higher concentration of virus in their immediate vicinity. So sure, it's layers of defense. The mask is also about limiting the emissions in the first place and distancing indoors is not always practical in public busy spaces.

But sure. It is not settled science. Science takes time. If your point is that we don't understand exactly what happens then sure, but we rarely do for anything in this field anyways.

the diamond princess is especially poor evidence, as it was an after-the-fact investigation (with heavy motivation to find something and gain early notoriety), not a study per se. what likely happened was that there were multiple social infection vectors (not of the long-distance air variety but more the drunk chatting variety) and the crew and passengers distorted their testimony to limit their own liability exposure. the diamond princess case was also the source of the "virus lives for weeks outside the body" mistruth because pcr tests readily amplify partial, dead viral dna/rna just as well as live virus (it has to be 'killed' to be amplified, after all).

but yes, viral concentration is higher near an infected person, but it falls off rapidly (to something like the 3rd power iirc) with distance and time, especially the latter of which being why incidental exposure in public places is unlikely to be material. it's also something a small minority of people have at a given time (on average less than 1% of those around you). it's mainly socializing for extended periods of time where masks can potentially help reduce infection (that's when we're also most likely to let our guard down).

i'd go so far as to posit that sociability (via variables like social graph size/breadth) is likely more correlated to infection than (the lack of) mask usage.

The diamond princess people also ate their meals in a shared space, IIRC. I think they changed that eventually, but by the time they did, the conclusion was hopelessly confounded.