40% of people with coronavirus have no symptoms. Might they be the key to ending the pandemic?

Chron.com:

A high rate of asymptomatic infection is a good thing,” said Gandhi, an infectious-disease specialist at the University of California at San Francisco. “It’s a good thing for the individual and a good thing for society.”

When researcher Monica Gandhi began digging deeper into outbreaks of the novel coronavirus, she was struck by the extraordinarily high number of infected people who had no symptoms.

A Boston homeless shelter had 147 infected residents, but 88% had no symptoms even though they shared their living space. A Tyson Foods poultry plant in Springdale, Ark., had 481 infections, and 95% were asymptomatic. Prisons in Arkansas, North Carolina, Ohio and Virginia counted 3,277 infected people, but 96% were asymptomatic.

During its seven-month global rampage, the coronavirus has claimed more than 700,000 lives. But Gandhi began to think the bigger mystery might be why it has left so many more practically unscathed.

What was it about these asymptomatic people, who lived or worked so closely to others who fell severely ill, she wondered, that protected them? Did the “dose” of their viral exposure make a difference? Was it genetics? Or might some people already have partial resistance to the virus, contrary to our initial understanding?

Efforts to understand the diversity in the illness are finally beginning to yield results, raising hope that the knowledge will help accelerate development of vaccines and therapies – or possibly even create new pathways toward herd immunity in which enough of the population develops a mild version of the virus that they block further spread and the pandemic ends.

“A high rate of asymptomatic infection is a good thing,” said Gandhi, an infectious-disease specialist at the University of California at San Francisco. “It’s a good thing for the individual and a good thing for society.”

The coronavirus has left numerous clues – the uneven transmission in different parts of the world, the mostly mild impact on children. Perhaps most tantalizing is the unusually large proportion of infected people with mild symptoms or none at all. The Centers for Disease Control and Prevention last month estimated that rate at about 40%.

Those clues have sent scientists off in different directions: Some are looking into the role of the receptor cells, which the virus uses to infiltrate the body, to better understand the role that age and genetics might play. Others are delving into masks and whether they may filter just enough of the virus so those wearing them had mild cases or no symptoms at all.

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Hans-Gustaf Ljunggren, a researcher at Sweden’s Karolinska Institute, and others have suggested that public immunity to the coronavirus could be significantly higher than what has been suggested by studies. In communities in Barcelona, Boston, Wuhan and other major cities, the proportion of people estimated to have antibodies and therefore presumably be immune has mostly been in the single digits. But if others had partial protection from T cells, that would raise a community’s immunity level much higher.

This, Ljunggren said, would be “very good news from a public health perspective.”

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