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VERIFY: You should wear a mask, recent Danish study doesn't prove otherwise

Some have claimed that a new study proves masks aren't effective. But its authors say otherwise, within the study's very text.

A study from Denmark released to the public this week is being shared as evidence that masks aren’t effective in slowing the COVID-19 pandemic.

Detractors point to the study’s conclusions that masks are less effective in protecting the person wearing them than conventional wisdom assumed.

But that doesn’t mean masks are useless in curbing the coronavirus’ spread. In fact, the researchers said that within the study’s text.

THE QUESTION

Is a recent study from the Copenhagen University Hospital in Denmark proof that face coverings and mask orders are useless in trying to prevent COVID-19 spread?

THE ANSWER

No. Experts have urged the public to wear masks to prevent the wearer from unknowingly spreading the virus to other people. This study only researched the potential for masks to protect the wearer, and did so in a setting where most of the general populace was not wearing masks themselves.

In fact, the researchers specifically wrote in their paper that it’s wrong to conclude you shouldn’t wear a mask based on their findings.

WHAT WE FOUND

The study was published in the Annals of Internal Medicine journal Wednesday. If you read through it, you’ll find that the researchers gathered a group of people in Denmark and gave half of them disposable surgical masks to wear out, and gave no masks to the other half. At the end of the study, they tested the participants for COVID-19 antibodies and found that 1.8% of the mask-wearing group had contracted COVID-19 while 2.1% of the no-mask group contracted the disease. The researchers said that their findings run contrary to assumptions that masks could reduce your own chance of contracting COVID-19 by 50%.

But the researchers also wrote within the study’s text itself, “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.”

What’s source control? Essentially, that’s limiting the spread of disease by reducing the ability of sick people to spread it to others.

That’s been the focus of the Centers for Disease Control and Prevention since they first recommended the general population wear masks earlier this year. While their webpage on mask considerations does say masks offer some protection to the wearer, they have greater confidence in masks’ ability to help protect those around you.

And the study’s findings don’t even entirely contradict the CDC’s claim that they may offer the wearer some protection. The press release for the study said, “While the evidence excludes a large personal protective effect of mask wearing, it weakly supports lesser degrees of protection, and cannot definitively exclude no effect.” That means that while it’s possible masks offered the wearer no personal protection, the study’s findings seem to suggest masks offer a small amount of protection to the wearer -- just not as much as 50% reduction in infection.

Regardless, the researchers were not able to test the effectiveness of masks in an ideal setting. The study said, “During the study period, authorities did not recommend face mask use outside hospital settings and mask use was rare in community settings. This means that study participants' exposure was overwhelmingly to persons not wearing masks.”

Denmark did not have a mask mandate at the time of the study and most of the Danish population were not wearing masks. Public health experts have argued COVID-19 spread is most reduced when all people in any given setting are wearing a mask. This study never got an opportunity to test that theory because of the nature of Denmark at the time.

Both the text of the study itself and the press release sent out alongside it reiterate that the study is not evidence that community-wide mask wearing is useless.

The study said, “The potential benefits of a community-wide recommendation to wear masks include combined prevention and source control for symptomatic and asymptomatic persons, improved attention, and reduced potential stigmatization of persons wearing masks to prevent infection of others. Although masks may also have served as source control in SARS-CoV-2–infected participants, the study was not designed to determine the effectiveness of source control.” There are long-established benefits to wearing a mask beyond any potential benefit to protect the wearer, and the study did not research those other potential benefits.

The press release went a step further by referencing CDC guidelines. “They also note that the US Centers for Disease Control recently updated their guidance to acknowledge that masks, when worn by all, may reduce transmission by both source control and personal protection. They say that the DANMASK-19 trial does not conflict with these guidelines, but shows that any contribution to risk reduction through personal protection is likely to be less than through source control.”

And there are recent studies that suggest masks are making a difference when it comes to COVID-19 in the United States. A late-October study from Vanderbilt University found that hospitalization rates in Tennessee counties without mask mandates have been rising faster than rates in the state's counties with mandates. And that study found hospitalization rates were the lowest in counties with the greatest percentage of their population wearing masks.

So yes, the findings from a recent Danish study do suggest that masks provide the wearer with limited protection. But these findings do not suggest masks are useless, nor do they contradict mask guidelines. One of the potential benefits of masks is their ability to reduce the likelihood the wearer spreads virus to others. The study did not research that. But other studies have found masks are having an impact in curbing the spread of COVID-19.

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