Finally a Properly-Controlled Study on Mask Effectiveness and Guess What It Shows

 


A new study is—as far as I know—the first truly controlled field experiment on mask effectiveness. The conclusion is that masks work. 

We already knew masks work because you can see it for yourself. But it's one thing to see that masks block droplets and another to know that this translates into meaningful protection at the community level.

This latest study involved 600 villages in Bangladesh, which have a combined population of 342,126 adults. Researchers randomly selected some of the villages to be in the treatment group and the rest were in the control group.  

For eight weeks, people in the treatment villages received free masks, information on the importance of masking, role modeling by community leaders, and in-person reminders. Villages in the control group received none of that.

Researchers visited the villages every week over the study period to observe how many people were properly wearing masks and social distancing at mosques, markets, the main entrance roads to villages, and tea stalls. At five and nine weeks they surveyed people about COVID-19 symptoms, and at 10-12 weeks they got blood samples to test for SARS-CoV-2 antibodies.

The intervention more than tripled proper mask wearing, from 13.3% in the control villages to 42.3% in the treatment villages. This effect continued through the experiment and when they checked two weeks after it ended. However, the effect faded to a 10% difference after five months.

There was also a measurable impact on infection rates. The treatment villages had 9.3% to 11.2% (depending on mask type promoted) lower prevalence of antibodies, and the difference was 34.7% for people 60 and older.  

This paper is still under review but it looks to me like it has very solid methodology. It addresses nearly all of the problems with other studies, like no control groups, small sample size, non-random sampling, and no observations of actual mask usage.  

Anti-maskers ignore these flaws if a study's findings support their beliefs. I wonder if they will find some way to spin this one, or if they will just ignore it.

Image by Juraj Varga from Pixabay 



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