“Our results suggest that the recommendation to wear a surgical mask when outside the home among others did not reduce, at conventional levels of statistical significance, the incidence of SARS-CoV-2 infection in mask wearers in a setting where social distancing and other public health measures were in effect, mask recommendations were not among those measures, and community use of masks was uncommon.”
The problem here being that it’s only testing the estimate of 5% protection provided to the wearer (from infection from someone without a mask who is infected), rather than the 70% estimate from the infected person if the infected person is wearing the mask, or the 95% estimate of protection if both infected & non-infected are wearing masks.
“Although the difference observed was not statistically significant, the 95% CIs are compatible with a 46% reduction to a 23% increase in infection” which the 5% reduction assumption is well within.
“Limitation: Inconclusive results, missing data, variable adherence, patient-reported findings on home tests, no blinding, and no assessment of whether masks could decrease disease transmission from mask wearers to others. ” So too many other variables to be confident of the data.