Mask this

Based on “the science,” Minnesota Governor Tim Walz is announcing another set of shutdown measures in yet another of his Joe Isuzu come-ons tonight. Coincidentally comes word of the long-awaited Danish mask study. It was finally published this morning. As expected, it found masks were generally not effective in protecting the wearer of the mask from infection by the Covid virus.

This was the largest-ever randomized controlled trial to test protective efficacy. The study was completed in September but the authors were unable to find a journal willing to publish the results until today. Here’s an excerpt (citation at bottom):

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 related New York Times story by Gina Kolata is “Danish Study Questions Use of Masks to Protect Wearers.” Kolata notes: “The study, published in the Annals of Internal Medicine, did not contradict growing evidence that masks can prevent transmission of the virus from wearer to others. But the conclusion is at odds with the view that masks also protect the wearers — a position endorsed just last week by the Centers for Disease Control and Prevention.”

This is also from Kolata’s story:

About 4,860 participants completed the study. The researchers had hoped that masks would cut the infection rate by half among wearers. Instead, 42 people in the mask group, or 1.8 percent, got infected, compared with 53 in the unmasked group, or 2.1 percent. The difference was not statistically significant.

“Our study gives an indication of how much you gain from wearing a mask,” said Dr. Henning Bundgaard, lead author of the study and a cardiologist at the University of Copenhagen. “Not a lot.”

Citation: “Effectiveness of Adding a Mask Recommendation to Other Public Health Measures to Prevent SARS-CoV-2 Infection in Danish Mask Wearers: A Randomized Controlled Trial.”

UPDATE/CORRECTION: I revised the first paragraph in the interest of clarifying the scope of the study consistent with the quotes above. I regret the inaccuracy of my original phrasing.

KEVIN ROCHE adds (link omitted):

I will do a fuller post soon, but the headline result–wearing a mask makes no difference in cases or in level of transmission in the community. It is obvious to all of us now that this is the case, as we can see the case growth in areas of the country with extremely high mask-wearing rates. Coupled with the withdrawal of the county study which purported to show a benefit based on limited time period study, this should put an end to any Governor claiming that mandates are backed by science and data, but it won’t. Expect to see all kinds of nonsense about how this isn’t a very valid study.

Kevin’s promised elaboration will appear at his Healthy Skeptic site.

KEVIN’S FULL POST on “The Danish mask study” is now up.

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