1. The Danish mask study is probably the only Randomized controlled trial conducted so far to study mask efficacy to prevent COVID. Blinding was of course not possible.
Remember that randomized trials provide superior data compared to observational ones.
acpjournals.org/doi/10.7326/M2…
Remember that randomized trials provide superior data compared to observational ones.
acpjournals.org/doi/10.7326/M2…
2. The primary outcome was SARS-CoV-2 infection in the mask wearer at 1 month by antibody testing, polymerase chain reaction (PCR), or hospital diagnosis.
3. A total of 3030 participants were randomly assigned to the recommendation to wear *surgical* masks, and 2994 were assigned to control; 4862 completed the study. Infection with SARS-CoV-2 occurred in 42 participants recommended masks (1.8%) and 53 control participants (2.1%).
4. The between-group difference was −0.3 percentage point (95% CI, −1.2 to 0.4 percentage point; P = 0.38) (odds ratio, 0.82 [CI, 0.54 to 1.23]; P = 0.335
5. Which means the difference was not statistically significant. The p value was greater than 0.05 and the odds ratio confidence interval crossed 1.0
6. For secondary outcomes the researchers also looked at the incidence of other viral respiratory illnesses being impacted by mask wearing and could not detect a statistically significant difference between mask and no mask wearing.
7. Note that the study used high quality surgical masks with a filtration rate of 98% and not cloth masks that are known to have a much lower and unpredictable efficacy on account of differences in manufacturing parameters and pore size.
8. The present findings are compatible with the findings of a review of randomized controlled trials of the efficacy of face masks for prevention (as personal protective equipment) against influenza virus.
9. The bottom line is that in a study powered to find statistical differences between treatment and control groups, they did not detect statistically significant differences. They did find a slightly decreased incidence of COVID in the mask intervention group compared to control.
10. To reiterate, this used high quality surgical masks in the context of a randomized study and not homemade or commercial cloth masks, which presumably will have even lower rates of efficacy.
11. The most important limitation according to me is that the trial did not address the effects of masks as source control or as protection in settings where social distancing and other public health measures are not in effect.
12. Regardless of your personal viewpoints on mask wearing, the bottom line is that masks provide at best mild to moderate protection if that.
13. If this was a study looking for FDA approval for either a prescription drug or a device, it would not have met any metric for efficacy and not meet any criterion for FDA approval.
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