Effectiveness of Mask Recommendation to Prevent SARS-CoV-2 (Randomized trial)
acpjournals.org
acpjournals.org
First, it's not testing the efficacy of wearing a mask: it's testing the efficacy of telling someone to wear a mask. This is explicitly stated in the "limitations" section.
Second, getting a decent control group is almost impossible. Essentially no one in modern society is unaware of COVID or the recommendation to wear a mask, and essentially no one had failed to form an opinion on whether or not they will comply with that recommendation. And indeed, "variable adherence" is another factor called out in the limitations.
The summary could be reworded "having one more doctor tell someone to wear a mask does not make them less likely to contract COVID-19."
This study is very much not about the efficacy of state- or nation- wide mask mandates.
That's not an accurate summary; that should be "having one more doctor tell someone to wear a mask does not have a large enough effect size on their likelihood of getting COVID-19 for this study to detect." They had 1.8% infected in the extra-recommendation group and 2.1% in the control group.
> Based on the lowest adherence reported in the mask group during follow-up, 46% of participants wore the mask as recommended, 47% predominantly as recommended, and 7% not as recommended."
Personally, I find it easy to believe that people were in fact wearing their masks. To be in the study you it looks like you had to joined voluntarily on your own accord, indicating a participant group with an interest in it:
> Recruitment involved media advertisements and contacting private companies and public organizations
If anything, I find it easy to believe that adherence would be less in the general population than in this study. Particularly stuff like wearing masks incorrectly, eg not covering the nose, leaving gaps, etc.
Edit: it actually looks like the study doesn't include that statistic at all, which is appallingly poor design.
Why do you think that? The study says "A total of 3030 participants were randomly assigned to the recommendation to wear face masks, and 2994 were assigned not to wear face masks".
At the time the study was performed (April and May 2020), it was not common to wear masks in Denmark outside of hospitals. In fact the authorities recommended against wearing masks because there was a shortage and the available masks should be reserved for high risk groups.
There is lots of evidence that wearing mask protects others, that's why surgeons wear surgical masks during surgery.
Surgical masks are not intended to protect the wearer, you need medical respirator for that. The question is how effective they are in doing job they are not designed to do. It seems to be limited, maybe around 30-50% depending on the study.
There is a lack of evidence for the effectiveness of masks during surgery, and they aren't always mandatory to wear:
https://www.cochrane.org/CD002929/WOUNDS_disposable-surgical...
https://www.medpagetoday.com/infectiousdisease/infectioncont...
https://ncbi.nlm.nih.gov/pmc/articles/PMC4480558/
There are obvious hygienic benefits - no-one wants to be splashed with bodily fluids - but there is a lack of evidence that they actually protect the patient.
Discussion
>a recommendation to wear a surgical mask when outside the home among others did not reduce, at conventional levels of statistical significance, incident SARS-CoV-2 infection compared with no mask recommendation.
Important however
> .. The findings, however, should not be used to conclude that a recommendation for everyone to wear masks in the community would not be effective in reducing SARS-CoV-2 infections, because the trial did not test the role of masks in source control of SARS-CoV-2 infection.
Is there any evidence that capturing heavier droplets has any material effect on transmission? No. And we know that transmission is driven by aerosols now. Aerosols are not heavy droplets.
Moreover, at this point, it isn’t challenging to find cities and states with high levels of mask compliance, and spiking cases:
https://mobile.twitter.com/ianmSC/status/1329187274794225666...
https://mobile.twitter.com/ianmSC/status/1329218665187745794...
https://mobile.twitter.com/yinonw/status/1329558423604695046...
https://mobile.twitter.com/ianmSC/status/1329610060125749251...
A great many preprints were created in the the spring (when cases were on the decline in the northern hemisphere) claiming to prove that masks “work”, based on the same kinds of observations. Now that cases are increasing in the northern hemisphere, I eagerly await a revisiting of those publications.
Frankly, I think it's been a huge mistake to discourage valved masks: they're much easier to breath in and more comfortable. Better to encourage the vulnerable to wear high quality, valved N95 masks and protect themselves, than worry about those same people infecting others.
My risk from COVID is something like 1/50th that of my parents.
Because I've seen that claim a lot. But never actually seen a scientific study making that claim.
Whether or not masks protect others seems much harder to isolate but there does seem to be lower R^2 values for countries and areas with more normalized mask wearing. Perhaps it is just a correlation (just seeing masks reminds people of the risk and they modify their behavior).
The purpose and design of surgical masks is to protect others, not the wearer. Mask catches big droplets but is not effective catching small particles. It's hard to wear tightly.
Respirator is designed to protect wearer. Buy N95 respirator and wear it correctly (trim your beard if necessary) if you want to be safe.
A respirator with an exhalation valve, protects the wearer but does not give as good protection to others as respirator without a valve.
I have personally been unable to find a single reliable study of mask efficiency, and the ones about N95 respirator efficiency that I found had the grim conclusion that they don't help much unless expertly fitted, and even health professional aren't very good to fitting them properly.
What I have found are some simulations that make unrealistic assumptions and reach the pre-supposed conclusions.
> Mask catches big droplets but is not effective catching small particles.
Well, then it's all a question of virion size vs mask hole size, then, and how long virions are still active, and what the effect of breath diffusion is. Of which the raw numbers would say that masks are mostly useless. I have not yet seen a model/study/trial that addresses this properly.
I wear an N95, and I encourage everyone else to do the same, but I do recognize that it's not a "fact"
Nobody would take a p-value of 0.38 as evidence. There are a lot of problems with p-values in general, but even uncritical fans of p-values would ignore any study with p = 0.38.
This is negative result.