Veterans attend a protest in Portland, Ore., on July 31.
Photo: caitlin ochs/ReutersFace masks have become a cultural symbol. To resist them “is nothing more than selfish, libertarian nonsense masquerading as a comic-book defense of freedom,” Thomas Friedman of the New York Times proclaims. Yet the science is far less certain than the moralism.
The question of how well masks prevent transmission and infection requires far more study. The decision to wear a mask would seem to be cost-free, apart from minor discomfort. But absolutism about masks and disregard for scientific uncertainties may promote a false sense of security that encourages risky behavior—including massive political protests.
In February, the Centers for Disease Control and Prevention recommended against wearing face masks and instead urged Americans to “take everyday preventive actions” like staying home when sick and washing hands. These recommendations were guided by the government’s desire to conserve medical masks for health-care workers.
The CDC changed its recommendation in April based on lab tests showing that cloth masks reduce the distance that large respiratory droplets travel after a cough. Like the flu, Covid-19 is believed to be transmitted mainly through these large droplets.
Media figures and public-health officials have also observed that countries where face-mask use is more prevalent have lower infections. In June, the New York Times ran a story with the headline “Is the Secret to Japan’s Virus Success Right in Front of Its Face?” Its answer: Yes. But this piece drew conclusions based on mere correlations. According to a YouGov survey in late June, face-mask use was higher in the U.S. (59%) than in countries with fewer infections, including Taiwan (57%), France (54%), Canada (35%), Netherlands (9%) and Denmark (2%). And Japan (77%) and Hong Kong (83%) have experienced recent infection spikes.
A study in the Journal of the American Medical Association this month reported that a universal mask policy for health-care workers and patients at the Mass General Brigham hospital system reduced Covid-19 infections. The positive test rate among health-care workers peaked at 21.32% in March, declined to 14.65% after masks were mandated for workers, and dropped further, to 11.46%, in late April after the mask mandate extended to patients.
But these numbers roughly track the overall positive test rate in the state. The study notes that the improvements “could be confounded by other interventions inside and outside of the health care system, such as restrictions on elective procedures, social distancing measures, and increased masking in public spaces, which are limitations of this study.”
The only way to ascertain the efficacy of face masks in the real world is to do randomized trials. So far there have been only a dozen examining the efficacy of masks in preventing respiratory illnesses, and conclusions have been difficult to draw because of poor compliance by study participants. None of the six trials published over the past decade found that masks alone had a significant effect on the spread of the flu or similar illnesses in health-care workers or the general population.
The only trial with reusable cloth masks suggested they’re ineffective. They could even increase the risk. In the 2015 study, hospital workers in Vietnam who were given cloth masks were 13 times as likely to develop influenza-like illnesses as those given surgical masks. Face masks are speculated to be more useful in preventing Covid-19 because many infected people are asymptomatic. But some three-fourths of flu cases are also asymptomatic, and most people who develop symptoms are infectious for a couple of days first.
A new independent analysis of cloth masks’ efficacy on the CDC website notes that the mask in the Vietnam trial was “a locally manufactured, double-layered cotton mask”—similar to what many Americans buy today—and that higher infection rates among wearers “may have been because the masks were not washed frequently enough or because they became moist and contaminated.”
“Cloth masks may give users a false sense of protection because of their limited protection against acquiring infection,” the researchers write. “Taking a mask off is a high-risk process because pathogens may be present on the outer surface of the mask and may result in self-contamination during removal.”
This is an important caveat: Fiddling with masks can be more dangerous than not wearing one at all. The American Academy of Pediatrics recommends that “elementary students should wear face coverings if the risk of touching their mouth or nose is not greater than the benefit of reducing the spread of COVID-19.” But the point is lost amid simplistic moralizing about selfish libertarians.
While mask mandates provide a comfort level that is needed to get people back to work and resume economic activity, they may also induce a false sense of security. In early April, as the Trump administration was debating whether to change its guidance on masks, Deborah Birx of the White House virus task force warned that “we don’t want people to get an artificial sense of protection because they’re behind a mask” or “send a signal that we think a mask is equivalent” to social distancing and good hygiene.
Liberal politicians—who railed against antilockdown protests in the spring—have dismissed concerns that leftist demonstrations could spread infection, because participants are wearing masks. But not all are, and many masks aren’t fitted correctly. Protesters probably don’t wash them regularly. And masks don’t eliminate the risk of contagion when large numbers of people are crowded for long periods while talking loudly and breathing heavily.
Masks have benefits, but moralism can be harmful to public health.
Ms. Finley is a member of the Journal’s editorial board.
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