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The science has not changed. KN95 masks still protect against covid.

The science has not changed. KN95 masks still protect against covid.

How to make sense of a study that seemed to imply that KN95 masks were no better than surgical masks in protecting against the coronavirus. In short: That was the wrong interpretation. A high-quality respirator mask provides better protection against respiratory viruses than lower-quality masks.

Now, there is more mask confusion thanks to the release of a new review of masks published by Cochrane Library. “We are uncertain whether wearing masks or N95/P2 respirators helps to slow the spread of respiratory viruses based on the studies we assessed,” the authors concluded.

Some have taken this to mean that masks don’t work to protect against the coronavirus. I received messages from concerned readers who are now doubting whether they should keep masking.

Jeff from Wyoming, for example, writes: “I am an immunocompromised 78-year-old and wonder if I should continue wearing a mask at places like stores, the YMCA and crowded restaurants. I wear masks in these situations but have read that masks are not efficacious.”

Jeff should keep wearing a mask in these settings if his goal is to reduce his chance of contracting the coronavirus. Unmasking because he thinks masks don’t work to protect him is a dangerous misinterpretation of the Cochrane findings.

First, I want to acknowledge that Cochrane is a highly reputable source. Its systematic reviews are considered the gold standard of medical analysis. But, as with all other research, any interpretation of its findings should take into account the methodology, the question being asked and the limitations.

In this case, reviewers examined 78 randomized controlled trials that looked at the impact of physical mitigation measures, including masking. These studies took place around the world. Many were conducted before covid and assessed the impact of masking on preventing influenza and other viral illnesses.

The main question the analysis reviewed was whether physical interventions can “interrupt or reduce the spread of acute respiratory viruses.” This is a population-level question — that is, it primarily asks whether masking reduces the spread of viruses in the community rather than whether it protects individuals from contracting the disease.

The authors acknowledge numerous limitations, the most significant of which is that in many of the studies, compliance with masking was low. And masks work only if they are worn consistently and properly.

Based on the Cochrane review, I think it’s fair to conclude that evidence doesn’t support masking to reduce community transmission if adherence is variable. Controlling highly contagious respiratory viruses such as omicron subvariants is extremely challenging, and intermittent masking is probably ineffective as a population-level intervention.

I also agree with the authors’ conclusion that we need more well-designed randomized controlled trials around masking and, crucially, an accounting of the harms of masking. In certain populations, such as young children, the harms might outweigh the potential benefits, especially if there is limited, if any, benefit of masking to protect others.

But it would be wrong to conclude from the review that everyone should stop masking because masks no longer protect the mask-wearer. Even if mask recommendations might not have a population effect, high-quality masks still work on an individual level if that person consistently wears them.

The science hasn’t changed: Well-fitting N95, KN95 or KF94 masks protect their wearers against covid and other respiratory diseases. John and others who are elderly, immunocompromised or otherwise want to avoid covid should continue wearing them in indoor crowded spaces.


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The science has not changed. KN95 masks still protect against covid. -