Masks Are a Tool, Not a Panacea
Surely it is reasonable to expect people who know they are infected with COVID-19 to isolate themselves so they won’t risk infecting others. But pre-symptomatic and asymptomatic people can unknowingly infect people too, wandering about in what amounts to an open-access health commons. Libertarians usually choose to enclose a commons by assigning property rights, so that owners can bear both the benefits and the costs of ownership. Alas, there isn’t an obvious way to erect a fence preventing infected people from causing harm to non-consenting others.
But what about wearing a mask? Is that an enclosure that will work?
At the beginning of the pandemic, several research groups produced initial assessments of masks’ efficacy in blunting the community transmission of the coronavirus. Most agreed that the available evidence either for masks or against them was of pretty poor quality.
For example, an April 2020 National Academies of Sciences, Engineering, and Medicine report on fabric masks’ effectiveness noted that “there are no studies of individuals wearing homemade fabric masks in the course of their typical activities” and added that “the current level of benefit, if any, is not possible to assess.”
Over the succeeding months, fortunately, more studies and analyses have been conducted. The general conclusion is that the widespread adoption of facial coverings in indoor and outdoor crowded spaces does help slow community transmission of COVID-19. As a result, the Centers for Disease Control and Prevention (CDC) updated its guidance last week to encourage facial coverings in community settings.
Initially, the recommendation to wear facial coverings was largely about “source control”—that is, preventing infected people from transmitting their microbes to non-consenting others. The latest CDC guidelines cited studies that suggest face masks can also protect their wearers by reducing their exposure to viral particles.
Let’s review some of the evidence behind the CDC’s recommendations.
A May article in Clinical Infectious Diseases reported a study in which two groups of hamsters were partitioned by surgical masking material. The healthy hamsters were separated from hamsters infected with COVID-19, with the researchers allowing unidirectional airflow from the infected group to the uninfected group. Two-thirds of the unprotected group became infected, whereas only 17 percent of those protected by surgical masks did. And the hamsters in the protected group that did become infected had milder symptoms and lower viral loads than those in the unprotected group.
In April, a team of researchers tested cloth masks made of varying materials, including cotton, silk, chiffon, flannel, various synthetics, and combinations thereof. “Overall, we find that combinations of various commonly available fabrics used in cloth masks can potentially provide significant protection against the transmission of aerosol particles,” they reported in the journal ACS Nano. In June, the journal Physics of Fluids described the results of tests on various facial coverings, including bandanas, folded handkerchief masks, stitched cotton masks, and masks commonly available at pharmacies. All of them significantly impeded the flow of droplets, with bandanas being the least effective and stitched cotton masks the most effective.
In August, some Duke scientists used a laser setup to compare the number of respiratory droplets transmitted through various masks over time while someone was speaking. Surgical masks were fairly effective at reducing respiratory droplets, while the bandanas and neck gaiters they tested were not. (To the researchers’ dismay, some media outlets misreported that neck gaiters were actually worse than no masks at all.) A subsequent study at Virginia Tech found that neck gaiters were about as effective as other cloth masks at blocking aerosols.
In August, another study reported the results from 94 experiment runs with combinations of eight different fabrics, five mask designs, and airflows to simulate both talking and coughing. The researchers noted that “facial coverings or masks can significantly reduce the airborne dispersion of aerosolized particles from exhalation.” As a result, “wearing masks when coupled with social distan
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