Revisiting the Science: Do Masks Stop COVID-19?

This post contains a video, which you can also view here. To support more videos like this, head to!


It’s been awhile since I’ve talked about COVID mitigation measures, but I wanted to circle back to this topic based on a HUGE new Cochrane review that has just been published about the effectiveness of masks. And the update is: masks work. Masks absolutely work to reduce the spread of COVID-19 in real world settings. Absolutely, without a doubt.

“But wait,” you may be saying, “my MAGA uncle says that Cochrane Review says masks don’t work. What’s going on?”

Well, what’s going on is that many years ago I read a study suggesting that if you want to educate people about misinformation, it’s important to state the facts very clearly and up front before you even get into the misinformation. So yeah. The preponderance of evidence collected over the past three years tells us that N95 masks are really, really good at slowing the spread of COVID-19, and other masks can also help, though not as much. Masks help keep sick people from blasting the virus into the air, and they help keep healthy people from breathing in those virus particles.

So, what’s all this about a Cochrane review? I’ve talked about these a lot in the past few years: they aren’t new studies, per se, but systematic reviews and meta-analyses that are supposed to look over the dozens or hundreds or even thousands of studies, choosing only those with the highest quality control, and weighing them all to deliver a consensus, like “Tylenol doesn’t really work for tension headaches” or “there’s no evidence that brain boosting supplements boost any brains.” 

So it’s a shame that when Cochrane took on something that has, stupidly, become very politicized, they didn’t do their usual “gold standard” job. 

The review is titled “Physical interventions to interrupt or reduce the spread of respiratory viruses,” and it is available in full online and as always I link to all my sources in the transcript which you can find linked below or at This review did conclude that “Wearing masks in the community probably makes little or no difference to the outcome of influenza-like illness/COVID-19 like illness compared to not wearing masks.”

Immediately, you might note that this is about “respiratory viruses,” and not specifically COVID-19. That’s important, because they lumped in a few studies on the effectiveness of masks versus COVID along with a whole bunch of studies on non-epidemic influenza, which is way less contagious and rarer to contract, meaning that of course you’re going to need way more data to show any result, compared to looking at masks in the middle of the COVID-19 pandemic. 

In fact, epidemiologist Gideon Meyerowitz-Katz decided to remove the data for influenza to see what would happen, and sure enough, the random controlled trials for masking DURING A PANDEMIC showed a clear, modest benefit. He points out that the review is perfectly fine otherwise, but personally I think it’s a pretty big deal that Cochrane released this during a pandemic, knowing that people would assume that the conclusion would be applied during a pandemic. It’s like releasing a review concluding there’s no benefit to wearing a seat belt, without mentioning that most of the data I examined was from a survey of people sitting in parked cars in the grocery store parking lot. It turns out that context is very important!

Unlike Meyerowitz-Katz, I’ve seen other epidemiologists, like Dr. Katelyn Jetelina (who I’ve recommended here in the past) who are critical of much more than just the influenza/COVID screw-up. Jetelina points out that the review only used randomized control trials (RCTs), which is usual for Cochrane and is something I’ve seen scientists criticize about them before. RCTs, in which you randomly assign part of a population to a treatment group and another part of the population to a control group, are very, very good at telling us the answer to certain questions, but not all questions. And in the case of masking during the past three years of the COVID-19 pandemic, we just don’t have very many RCTs to examine, so not only did this review look at different viruses but also different settings, from community spread to hospital settings where healthcare workers sometimes wore masks and sometimes didn’t. Real world data examining what people are actually doing shows unequivocally that masking during this pandemic, especially with N-95s, reduces transmission. The more you mask, the lower your chance of getting COVID. The more people mask AROUND YOU, the lower your chance of getting COVID.

The Cochrane authors’ conclusions are valid, if your MAGA uncle would have bothered to read that far: “The high risk of bias in the trials, variation in outcome measurement, and relatively low adherence with the interventions (i.e. people just didn’t wear masks) during the studies hampers drawing firm conclusions.” And “There is a need for large, well-designed RCTs addressing the effectiveness of many of these interventions in multiple settings and populations, as well as the impact of adherence on effectiveness, especially in those most at risk of (acute respiratory infections).”
It’s absolutely okay if the end result of a systematic review is “Hey, we need more data to fully understand the efficacy of this intervention during a pandemic,” and I really wish they had read the room and made that the obvious takeaway, here. I wonder how much of this review was influenced by past criticisms from scientists who say Cochrane takes far too long to make useful recommendations: personally, I’d rather they take their time and get it right rather than cobble together studies that aren’t actually relevant to our current situation. We were already facing an uphill battle when it comes to convincing people to do the very basic, obvious good thing of just putting a damn mask on when you’re inside public places where case counts are high. If we can’t even get the “gold standard” of systematic reviews to understand the problem, I’m afraid this battle is lost.

Rebecca Watson

Rebecca is a writer, speaker, YouTube personality, and unrepentant science nerd. In addition to founding and continuing to run Skepchick, she hosts Quiz-o-Tron, a monthly science-themed quiz show and podcast that pits comedians against nerds. There is an asteroid named in her honor. Twitter @rebeccawatson Mastodon Instagram @actuallyrebeccawatson TikTok @actuallyrebeccawatson YouTube @rebeccawatson BlueSky

Related Articles

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Back to top button