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A new theory asks whether wearing a mask is a raw COVID-19 vaccine.

The age-old concept of deliberately exposing people to a pathogen in order to create a protective immune response was first attempted against smallpox and paved the way for the rise of modern vaccines.

As the world waits for a safe and effective coronavirus vaccine, a team of researchers has come up with a provocative new theory: masks could help grossly immunize some people against the virus.

The unproven idea described in a comment posted in last week The New England Journal of Medicine, is inspired by the age-old concept of variolation, the deliberate exposure to a pathogen in order to create a protective immune response. Tried first against smallpox, the risky practice eventually fell out of favor, but paved the way for the rise of modern vaccines.

Masked exposures are not a substitute for a real vaccine. However, data from animals infected with the coronavirus, as well as evidence from other illnesses, suggest that masks, by reducing the number of viruses that hit a person̵

7;s airways, reduce the likelihood of the wearer getting sick.

And if a small number of pathogens still slip through, they could cause the body to produce immune cells that can remember the virus and stick with it to fight it off again.

“You can have this virus but you can be asymptomatic,” said Dr. Monica Gandhi, an infectious disease doctor at the University of California at San Francisco and one of the authors of the comment. “So if you can increase the rate of asymptomatic infections with masks, it may become a way of diversifying the population.”

That doesn’t mean people should wear a mask to purposely vaccinate themselves with the virus. “This is not the recommendation at all,” said Gandhi. “There are no smallpox parties either,” she added, referring to social gatherings where the healthy and the sick meet.

The theory cannot be directly proven without clinical studies comparing the results of people masked in the presence of the coronavirus to those who are not – an unethical experimental setup. External experts, while intrigued by the theory, were reluctant to accept it without further data and advised careful interpretation.

“It seems like a leap,” said Saskia Popescu, an Arizona-based infectious disease epidemiologist who was not involved in the comment. “We don’t have much to support.”

A new theory asks whether wearing a mask is a raw COVID19 vaccine

Data suggests that wearing masks reduces the number of viruses entering a person’s airways and reduces the likelihood of the wearer getting sick.

Wrongly seen, the idea could lull the masked person into a false sense of complacency and potentially put them at higher risk than before, or perhaps even reinforce the misconception that face coverings against the coronavirus are completely useless as they cannot make the wearer impervious to the Infection.

“We still want people to follow all other prevention strategies,” said Popescu. That means staying vigilant to avoid crowds, physical distancing, and hand hygiene – behaviors that overlap in their effects but cannot substitute for one another.

The coronavirus variolation theory is based on two assumptions that are difficult to prove: lower doses of the virus lead to less severe illness, and mild or asymptomatic infections can promote long-term protection against subsequent attacks. Although other pathogens set a precedent for both concepts, evidence for the coronavirus remains sparse, partly because scientists only had a few months to study the virus.

Experiments on hamsters have suggested a relationship between dose and disease. Earlier this year, a team of researchers in China found that hamsters housed behind a barrier made of surgical masks are less likely to be infected by the coronavirus. And those who contracted the virus got sick less than other animals without a mask to protect them.

Some observations in humans appear to support this trend as well. Infection rates appear to decrease in crowded environments where masks are prevalent. And while face coverings may not block all incoming virus particles for everyone, it appears to be associated with less disease. Researchers have discovered largely silent, symptom-free outbreaks in locations from cruise ships to food processing plants, all of which are full of mostly masked people.

Data linking dose to symptoms has been collected for other microbes that attack the human respiratory tract, including influenza viruses and the bacteria that cause tuberculosis.

Despite decades of research, the mechanics of air transfer remains largely “a black box,” said Jyothi Rengarajan, a vaccine and infectious disease expert at Emory University who was not involved in the comment.

This is in part because it is difficult to determine the dose of infection it takes to make a person sick, Rengarajan said. Even if researchers ultimately settle on an average dose, the outcome will vary from person to person, as factors like genetics, a person’s immune status, and the architecture of their nasal passages can all affect how much virus can colonize the airways.

Confirming the second half of the theory of variolation – that masks allow entry into just enough viruses to activate the immune system – could be even more difficult. Although several recent studies have suggested the possibility that mild cases of COVID-19 can provoke a strong immune response to the coronavirus, lasting protection cannot be demonstrated until researchers collect data on infections for months or years after they have subsided.

Overall, the theory “has some merits,” said Angela Rasmussen, a Columbia University virologist who was not involved in the comment. “But I’m still pretty skeptical.”

It was important to remember that vaccines are inherently less dangerous than actual infections, which is why practices like variolation (sometimes called vaccination) are eventually becoming obsolete. Before vaccines were discovered, doctors rubbed smallpox, or pus, into the skin of healthy people. The resulting infections were usually less severe than typical smallpox cases, but “people definitely got smallpox and died of variolation,” Rasmussen said. And, unlike vaccines, variolation can make people contagious to others.

Gandhi acknowledged these limitations and noted that the theory should not be construed as anything else – as a theory. Even so, she said, “Why not increase the chance not to get sick and have some immunity while we wait for the vaccine?”

Katherine J. Wu c.2020 The New York Times Company

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