Masks are Effective, Despite One Flawed Study From Denmark

“I think the overwhelming body of evidence suggests that masks are effective,” the lead author of a study recently cited by America’s Center for Disease Control told the Washington Post.

They were responding to another (very controversial) outlier study whose findings “conflict with those from a number of other studies,” according to the New York Times, citing numerous experts. “Critics were quick to note [that] study’s limitations, among them that the design depended heavily on participants reporting their own test results and behavior, at a time when both mask-wearing and infection were rare in Denmark.”

The Washington Post reports:

In the large, randomized study published Wednesday in the Annals of Internal Medicine, researchers observed more than 6,000 people in Denmark from April to June when mask-wearing was not required in the country. Fewer people in the group that was advised to wear masks contracted the virus — or about a 14 percent reduced risk because of mask-wearing — but the difference was not statistically significant, indicating that the medical masks issued were not particularly effective at preventing the wearers from being infected. Other experts, however, argue that the study was conducted when there was relatively less community spread of the virus and that testing the participants’ antibodies cannot reliably measure whether they had the virus during the time of the study.

“We think you should wear a face mask at least to protect yourself, but you should also use it to protect others,” lead author Henning Bundgaard told The Washington Post. “We consider that the conclusion is we should wear face masks.” Bundgaard said even the small risk reduction masks offer “is very important, considering it is a life-threatening disease…”

“Because the issue has become so politicized, there’s a real risk — and it’s already being used in this way — that studies like this will be sort of cherry-picked and presented as conclusive evidence that masks are completely ineffective,” Columbia University virologist Angela Rasmussen said… In letters and blog posts, public health experts express concern about the design of the study and warn that policymakers could misinterpret the research to mean that masks are ineffective. “However, the more accurate translation is that this study is uninformative regarding the benefits (or lack thereof) of wearing masks outside of the healthcare setting,” one letter states. “As such, we caution decision-makers and the media from interpreting the results of this trial as being anything other than artifacts of weak design.”
Even the Denmark study itself acknowledged its own limitations, citing “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.”

And it also acknowledges large gaps in adherence to proper mask usage among its participants: “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.”

The Post notes that America’s Center for Disease Control reiterated that people do benefit from wearing a mask that can filter out virus-carrying droplets, and last week “cited multiple studies evaluating mechanical evidence that concluded masks can block certain respiratory particles, depending on the material of the mask…”

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