> 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.