"Researchers have long known that masks can prevent people from spreading airway germs to others — findings that have driven much of the conversation around these crucial accessories during the coronavirus pandemic. But now, as cases continue to rise across the country, experts are pointing to an array of evidence suggesting that masks also protect the people wearing them, lessening the severity of symptoms, or in some instances, staving off infection entirely.
Different kinds of masks “block virus to a different degree, but they all block the virus from getting in,” said Dr. Monica Gandhi, an infectious disease physician at the University of California, San Francisco. If any virus particles do breach these barriers, she said, the disease might still be milder.
Dr. Gandhi and her colleagues make this argument in a new paper slated to be published in the Journal of General Internal Medicine. Drawing from animal experiments and observations of various events during the pandemic, they contend that people wearing face coverings will take in fewer coronavirus particles, making it easier for their immune systems to bring any interlopers to heel.
Dr. Tsion Firew, an emergency physician at Columbia University who wasn’t involved in the work, cautioned that the links between masking and milder disease haven’t yet been proved as cause and effect. Even so, the new paper “reiterates what we say about masks,” she said. “It’s not just a selfless act.”
Ideas about the importance of viral dose in the development of disease have cropped up in the medical literature since at least the 1930s, when two researchers formally noted that mice exposed to larger quantities of germs were more likely to die. More recently, scientists have gone as far as to puff different amounts of a flu virus up the noses of human volunteers. The more virus in this nasal plume, they found, the likelier the participants were to get infected and experience symptoms. That sort of experiment can’t be done ethically for the new coronavirus, given how dangerous it is. But earlier this year, a team of researchers in China tried something similar in hamsters: They housed coronavirus-infected and healthy animals in adjoining cages, some of which were separated by buffers made of surgical masks. Many of the healthy hamsters behind the partitions never got infected. And the unlucky animals who did got less sick than their “maskless” neighbors. Some indirect data has been accumulating from people as well. Researchers have tentatively estimated that about 40 percent of coronavirus infections do not produce any symptoms. But when some people wear masks, the proportion of asymptomatic cases seems to skyrocket, reportedly surpassing 90 percent during one outbreak at a seafood plant in Oregon. Wearing a face covering doesn’t make people impervious to infection, but these trends of asymptomatic cases could suggest that masks lead to milder disease, potentially reducing hospitalizations and deaths.
Particularly compelling, Dr. Gandhi said, is the data from cruise ships, which pack big groups of people into close quarters. More than 80 percent of those infected aboard Japan’s Diamond Princess in February — before masking had become common practice — came down with symptoms, she noted. But on another vessel that left Argentina in March, and on which all passengers were issued surgical masks after someone onboard came down with a fever, the level of symptomatic cases was below 20 percent.
Some independent experts say the paper is a welcome update, given the pervasive idea that wearing a mask is a mostly altruistic act.
“It’s been a real deficiency in the messaging about masking to say that it only protects the other,” said Charles Haas, an environmental engineer and expert in risk assessment at Drexel University. “From the get go, that never made sense scientifically.”
In other settings, too, from hospitals to hair salons, face coverings may have driven down rates of overall infection, perhaps preventing disastrous outbreaks. And countries like Japan, Taiwan and South Korea, where outbreaks quickly sparked a wave of widespread masking, managed to rein in the number of coronavirus-related hospitalizations and deaths early on.
Even in the United States, the slow upward tick in mask-wearing has coincided with what appears to be a more modest death rate, compared to the surge that occurred after the virus first made landfall in North America. These trends have also likely been influenced by increased testing, a downward shift in the average age of people contracting the virus and improvements in coronavirus treatments. Still, masks probably aren’t hurting things, Dr. Gandhi said.
The idea that face coverings can curb disease severity, although not yet proven, “makes complete sense,” said Linsey Marr, an expert in virus transmission at Virginia Tech. “It’s another good argument for wearing masks.”