Wearing a face mask may stave off severe infection with SARS-CoV-2, the virus that causes COVID-19, or could prevent infection entirely, a growing body of research suggests.
Masks “really are protective of you as an individual,” Monica Gandhi, an infectious disease physician at the University of California, San Francisco, tells NPR. That physical barrier—while not impervious to viral penetration—blocks some viral particles from getting into the body, she says. Reducing the amount of exposure could allow the immune system to neutralize the invaders, potentially resulting in a milder infection or no infection at all. She and colleagues present the idea and supporting evidence from animal studies and observational COVID-19 reports in more detail in a paper slated to appear next week in the Journal of General Internal Medicine.
This connection between wearing a mask and milder COVID-19 disease is still correlational and has not been shown as causative, Tsion Firew, an emergency physician at Columbia University who wasn’t involved in the work, tells The New York Times. But it “reiterates what we say about masks,” she says. “It’s not just a selfless act.” In other words, masks don’t just protect those around the wearer from exposure.
Gandhi and her colleagues describe past studies that show that the higher the dose of a virus a mouse receives, the more likely that animal is to die. The team also describes an experiment in which researchers sprayed varying levels of flu virus into the noses of human volunteers. The higher dose of the flu in the spray, the more likely the volunteer was to develop an infection and become ill.
And it appears masks can reduce the dose of the virus that enters the body. Recently, a study in hamsters showed that a barrier made of surgical mask material between animals infected with SARS-CoV-2 and healthy hamsters tamped down the spread of the virus.
“If [the hamsters] were masked they were less likely to get infection, and then even if they got infection they got mild infection,” Gandhi tells Fox Television Stations.
Data from viral outbreaks on cruise ships and poultry plants align with the findings of the hamster study. An analysis of infections of passengers and crew on a cruise ship that departed from Argentina in March showed that after the first reported case of COVID-19, all 217 passengers and crew were given masks, and of the 128 people who eventually contracted the virus, 81 percent were asymptomatic—a much higher proportion than expected. About 40 percent of cases are usually asymptomatic, Gandhi tells The Washington Post. In their paper, Gandhi and colleagues cite several other examples of masks correlating to higher rates of asymptomatic cases, indicating masks are protective not only of others but also the person wearing the mask.
“It’s been a real deficiency in the messaging about masking to say that it only protects the other,” Charles Haas, an environmental engineer and expert in risk assessment at Drexel University who was not involved in the latest work, tells the Times. “From the get go, that never made sense scientifically.”