Masks offer some protection against COVID-19 infection, but not nearly as much as the authorized vaccines. By telling the public they have to continue masking after immunization, we all but guarantee skeptics will forgo both shots and masks.
The CDC caused an uproar in late July when it again recommended that fully vaccinated individuals mask up to reduce the spread of the SARS-COV-2 Delta variant. We published two articles in response to the agency's new guidelines. Dr. Josh Bloom explained why CDC's proposal is a logistical nightmare, and I argued that recommending masks for the immunized undermines the campaign to get more people vaccinated.
The lively responses to both stories drifted away from vaccine efficacy into a debate over the benefits of masking. The CDC's proposal was pointless, some said, because there's no evidence that masks work. Nonsense, others hit back; there's plenty of research showing that masks prevent infection.
I contend that both sides are wrong. Wearing a mask is better than doing nothing, particularly in health care settings, but it offers very little protection compared to getting immunized. With highly effective vaccines available, telling the public to wear face coverings and get shots encourages them to do neither.
The messy science behind masking
Right out of the gate, I want to emphasize that masks offer some level of protection. Since respiratory viruses like SARS-COV-2 are transmitted in aerosols and droplets, it only makes sense that putting a mask over your nose and mouth would decrease their spread and thus the chances of you infecting someone else. The key question is, “how much of a risk reduction are we talking about?” It depends on which study you read.
Several papers have shown that even a "cloth mask is better than no mask in preventing the spread of infection from an infected person to a healthy one," though it offered very little protection to an uninfected wearer. The risk reduction increases with the quality of the mask. The World Health Organization (WHO) also sponsored a systematic review in June 2020 which found that “face mask use could result in a large reduction in risk of infection,” perhaps more than 80 percent in some cases.
But the situation is more complicated than that. As another review, published in January 2021, noted, most of the research WHO examined looked at masking in health care facilities. Only three studies were conducted in community settings, and those were performed before the current pandemic. Importantly, none of the papers considered the relative risks of different masks, and they all looked at masking implemented alongside physical distancing, hand washing, and eye protection. Here's the reviewers summary:
Overall, evidence from [randomized controlled trials] and observational studies is informative, but not compelling on its own … [W]e do not know whether the results from influenza or SARS will correspond to results for SARS-CoV-2, and the single observational study of SARS-CoV-2 might not be replicated in other communities. None of the studies looked specifically at cloth masks.
A 2011 review by the highly respected Cochrane Collaboration found that “masks were the best performing intervention across populations, settings, and threats.” However, an April 2020 pre-print with the same lead author evaluated the efficacy of masks alone and concluded that “there was insufficient evidence to provide a recommendation on the use of facial barriers without other measures.” An updated Cochrane review published in November 2020 reached a similar conclusion, finding that
The pooled results of randomized trials did not show a clear reduction in respiratory viral infection with the use of medical/surgical masks during seasonal influenza.
These results are mixed, and that's likely because they're biased by dozens of variables that are very difficult to control for. The authors of a December 2020 article reviewing 33 studies, including 12 randomized controlled trials, summarized the challenge of studying the effects of masking:
While RCTs might underestimate effects due to poor compliance and controls wearing masks, observational studies likely overestimate effects, as mask wearing might be associated with other risk-averse behaviors.
Wearing face masks may reduce primary respiratory infection risk, probably by 6-15%. It is important to balance evidence from RCTs and observational studies when their conclusions widely differ and both are at risk of significant bias. COVID-19-specific studies are required.
In August 2021, we now have some COVID-specific masking studies. For example, a June 2021 modeling paper published in Science confirmed that mask efficacy was largely determined by the amount of airborne virus people are exposed to. “On the basis of direct measurements of SARS-CoV-2 in air samples and population-level infection probabilities,” the researchers wrote, “we find that the virus abundance in most environments is sufficiently low for masks to be effective in reducing airborne transmission.”
But, as always, the situation is more complicated in the real world. According to a May pre-print published on medRXiv:
Our main finding is that mask mandates and use are not associated with lower SARS-CoV-2 spread among US states. 80% of US states mandated masks during the COVID-19 pandemic. Mandates induced greater mask compliance but did not predict lower growth rates when community spread was low (minima) or high (maxima).
This study, too, had its limitations: it only tracked statewide trends of confirmed and probable COVID-19 infections, which could have obscured the impacts of masking on hospitalizations and deaths. There also may have been differences between cities or counties that were minimized by aggregated state statistics. Nonetheless, the paper's results match previous studies and are worth taking seriously.
I want to stress before moving on that the authors of these studies generally endorsed universal masking in the context of a pandemic, which underscores an important point: it's possible to accept the benefits of an intervention and acknowledge its limitations—to entertain two thoughts at the same time. This kind of nuance allows us to prioritize which interventions we pursue.
Vaccines > masks
In contrast to studies of mask efficacy, the data on immunization are far less variable. Vaccine clinical trials and follow-up studies aren't biased by a lack of compliance, for example, because the researchers administer the intervention at prescribed doses and intervals. Moreover, scientists don't have to account for different types of shots as they do with masks; the studies compare a vaccine to a placebo or another vaccine. There's no concern about properly fitting a vaccine to your face nor reusing a shot. Finally, there are many studies validating the efficacy of the authorized COVID shots in health care and community settings.
I'm being a bit pedantic, but the point is clear. It's much easier to conduct vaccine efficacy studies and thus to issue evidence-based immunization guidelines than to do so with masks. In his analysis of a new paper that confirmed the efficacy of the Pfizer and Moderna shots against Delta, Dr. Chuck Dinerstein put it this way:
Vaccination reduces disease severity for those infected and reduces their ability to transmit the disease to others. It does not eliminate transmissibility or your risk–that would be a miracle, not a medicine. Vaccination remains the key; it is the most protective option for ourselves and those around us.
But it's very difficult to make that case for vaccination to a frustrated public who has watched confusing masking and immunization guidance come and go over the last year and a half. Consider these highlights:
- "Seriously people," the Surgeon General tweeted last February, "STOP BUYING MASKS! They are NOT effective in preventing general public from catching #Coronavirus, but if healthcare providers can't get them to care for sick patients, it puts them and our communities at risk!"
- Actually, masks help prevent infection, the CDC announced last April.
- In fact, masks are probably better than the vaccines will be, then-CDC director Robert Redfield said in September 2020.
- Alright, masks aren't that effective, the agency acknowledged, but you should wear one even after you're vaccinated.
- We changed our minds; vaccines provide sufficient protection; leave the mask at home.
- We changed our minds again; Delta is on the loose, so mask up.
At the same time, the CDC says "available evidence suggests that the COVID-19 vaccines presently authorized in the United States offer protection against known emerging variants, including the Delta variant, particularly against hospitalization and death."
These mixed signals have to stop. We can't tell people the pandemic "could be ended once and for all if everyone would get vaccinated," as Dr. Anthony Fauci did on Friday, and urge them to mask up (a far less effective intervention) just in case the vaccines don't work as intended. With millions of Americans still on the fence about the shots, we are sending the worst possible message.