Forty percent of people with coronavirus infections have no symptoms. Might they be the key to ending the pandemic? - Bio-Defense Network
Aug 2020

Forty percent of people with coronavirus infections have no symptoms. Might they be the key to ending the pandemic?

New research suggests that some of us may be partially protected due to past encounters with common cold coronaviruses.

Ariana Eunjung Cha writes in the Washington Post that 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.

Boston homeless shelter had 147 infected residents, but 88 percent had no symptoms even though they shared their living space. A Tyson Foods poultry plant in Springdale, Ark., had 481 infections, and 95 percent were asymptomatic. Prisons in Arkansas, North Carolina, Ohio and Virginia counted 3,277 infected people, but 96 percent 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 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 no symptoms. The Centers for Disease Control and Prevention last month estimated that rate at about 40 percent.

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 face masks and whether they may filter just enough of the virus so that those wearing them had mild cases or no symptoms at all.

The theory that has generated the most excitement in recent weeks is that some people walking among us might already have partial immunity.

Summary of testing studies from around the world showing the share of people who tested positive for the coronavirus but had no symptoms (Tim Meko)

When SARS-CoV-2 was first identified on Dec. 31, 2019, public health officials deemed it a “novel” virus because it was the first time it had been seen in humans who presumably had no immunity from it whatsoever. There’s now some very early, tentative evidence suggesting that assumption might have been wrong.

One mind-blowing hypothesis — bolstered by a flurry of recent studies — is that a segment of the world’s population may have partial protection thanks to “memory” T cells, the part of our immune system trained to recognize specific invaders. This could originate from cross protection derived from standard childhood vaccinations. Or, as a paper published Tuesday in Science suggested, it could trace back to previous encounters with other coronaviruses, such as those that cause the common cold.

“This might potentially explain why some people seem to fend off the virus and may be less susceptible to becoming severely ill,” National Institutes of Health Director Francis Collins remarked in a blog post this past week.

On a population level, such findings, if validated, could be far-reaching.

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 serology studies. In communities in Boston, Barcelona, 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.”

Some experts have gone so far as to speculate whether some surprising recent trends in the epidemiology of the coronavirus — the drop in infection rates in Sweden where there have been no widespread lockdowns or mask requirements, or the high rates of infection in Mumbai’s poor areas but little serious disease — might be due to preexisting immunity.

Others say it’s far too early to draw such conclusions. Anthony S. Fauci, the United States’ top infectious-disease expert, said in an interview that while these ideas are being intensely studied, such theories are premature. He agreed that at least some partial preexisting immunity in some individuals seems a possibility.

And he said the amount of virus someone is exposed to — called the inoculum — “is almost certainly an important and likely factor” based on what we know about other viruses.

But Fauci cautioned there are multiple likely reasons — including youth and general health — that determine whether a particular individual shrugs off the disease or dies of it. He also emphasized that even those with mild illness may have lingering medical issues.

That reinforces the need, in his view, for continued vigilance in social distancing, masking and other precautions.

“There are so many other unknown factors that maybe determine why someone gets an asymptomatic infection,” Fauci said. “It’s a very difficult problem to pinpoint one thing.”

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