Masks may help reduce viral dose, some experts say
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.
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. Even so, the new paper “reiterates what we say about masks,” she said. “It’s not just a selfless act.”
Some indirect data has been accumulating from people as well. Researchers have tentatively estimated that about 40% 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% 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, Gandhi said, is the data from cruise ships. More than 80% 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%.
“It’s been a real deficiency in the messaging about masking to say that it only protects the other,” said Charles Haas, an expert in risk assessment at Drexel University. “From the get go, that never made sense scientifically.”