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Home » Evidence of the effectiveness of masks to prevent COVID is mixed

Evidence of the effectiveness of masks to prevent COVID is mixed

The use of face masks for the prevention of the spread of COVID-19 was a large subject of both scientific and political discussion during the nearly three years of the pandemic. People seem to choose to wear their masks as both medical and political statements. I know I did

But what are the facts about the effectiveness of the cloth and surgical masks that were used widely? That’s where it gets a bit fuzzy — the evidence was all over the place.

A new peer-reviewed study reviewed some of the better studies on the effectiveness of masks in preventing COVID-19 infections. If you were hoping for solid, unequivocal conclusions, the results still are mixed.

So, we are going to review this new review and find out what it tells us about the use of masks during the COVID-19 pandemic.

woman in brown dress holding white plastic bottle painting
Photo by Yaroslav Danylchenko on

COVID-19 and masks paper

A review paper published on 16 May 2023 in the respected Annals of Internal Medicine, by Roger Chou, MD, and Tracy Dana, MLS, both of Oregon Health & Science University in Portland, is the ninth in a series of reviews. The first eight looked at a total of two randomized clinical trials (RCTs) and 10 observational studies. This new study included three RCTs and 21 observational studies.

Here are some of their key results:

  • One good-quality Danish RCT, with 6024 participants, found that a recommendation for mask use was associated with a small but statistically insignificant reduction in COVID risk. In other words, the study could find no statistical difference between using or not using masks. However, adherence to wearing masks by the group that was supposed to wear masks was suboptimal, so that may have biased the results.
  • The strength of evidence remained low for reduced risk for SARS-CoV-2 infection with surgical masks versus no mask on the basis of two prior randomized controlled trials.
  • There were no new studies and insufficient evidence for differences in effectiveness for surgical versus cloth masks and N95 versus surgical masks.

The authors concluded:

Updated evidence suggests that masks may be associated with a small reduction in risk for SARS-CoV-2 infection in community settings. Surgical masks and N95 respirators may be associated with similar infection risk in routine patient care settings, but a beneficial effect of N95 respirators cannot be ruled out.

In other words, masks may provide a small reduction in the risk of COVID-19. From my perspective, wearing masks and getting fully vaccinated reduces the risk of infection and hospitalization, so that may be enough.

In an accompanying editorial, editor-in-chief Christine Laine, MD, MPH, and deputy editor Stephanie Chang, MD, MPH of Annals of Internal Medicine wrote:

There is evidence that masks could work to prevent COVID-19, but substantial gaps remain about whether they do work and under what conditions.

In the face of future viral outbreaks, we must move quickly to fill the gaps with timely studies that avoid the limitations of studies done to date. We may never reach definitive truth about when the benefit of masking interventions outweighs the harms, but it is imperative that we design studies that fill information gaps, interpret the evidence accurately, and are honest about what we do and do not know with certainty when making decisions and setting policy about masking.

In an accompanying opinion piece, Tara Palmore, MD, of George Washington University in Washington, D.C., and David Henderson, MD, of the NIH, stated that the wearing of masks in healthcare settings should remain. They wrote:

Real-world experience shows the effectiveness of mask wearing in clinical settings. Thanks largely to universal masking and use of other personal protective equipment, healthcare personnel have been at far greater risk for acquiring COVID-19 from community than occupational exposures. Transmission from patient to staff and staff to patient when both are masked does occur but is uncommon.

person wearing white face mask
Photo by Griffin Wooldridge on


So there you have it, a big giant “we don’t know” regarding masks and COVID-19 infections. The problem is what do we do when the next pandemic hits (probably a dangerous flu)?

We have weak evidence that masks work and we have weak evidence that masks don’t work. Some would argue that the precautionary principle applies — masks do not have any adverse effects, so even if there is a minor reduction in the risk of contracting a disease, it’s worth wearing. And remember, even a 1% reduction in risk can mean saving thousands of lives.

Despite the wish to make mask mandates some sort of test of political will, it really isn’t. There is just enough evidence that masks save lives that I’m willing to put up with a bit of inconvenience and wear the mask. And when I see another person wearing a mask, we eyeball each other and give a slight nod of the head. Like we know something.


Michael Simpson

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