Most coronavirus cases spread from people with no symptoms, CDC says in new report

Morgan McFall-Johnsen
·4 min read
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A diner has his temperature checked at Manhattan restaurant Daniel on September 30, 2020, the first day that indoor dining is allowed in New York City since the beginning of the coronavirus outbreak. Carlo Allegri/Reuters

As coronavirus cases surge higher than ever before across the US, it's important to remember that most of them spread from people with no symptoms.

That includes people who have not yet developed symptoms but may fall ill as their infection progresses. Research shows that people "who feel well and may be unaware of their infectiousness to others" likely account for more than 50% of COVID-19 transmissions, the Centers for Disease Control and Prevention said in a science update on Friday.

That could happen at your Thanksgiving table, warns Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases.

"Right now today, in mid to late November, we're finding that innocent occurrences such as groups of friends and family meeting indoors because of the cold weather for dinner are becoming a major source of asymptomatic spread," he said during a virtual lecture for the University of Virginia School of Medicine on Wednesday. "That seems to be driving infections much more so now than the more obvious settings of bars and other places."

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Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, on June 30, 2020. Al Drago/AFP via Getty Images

The CDC report stressed that masks help reduce asymptomatic spread since they can protect both the mask-wearer and the people around them.

That why experts like Fauci have said the US would benefit from a nationwide mask mandate. If 95% of Americans had started wearing masks at the end of September, it could have saved nearly 130,000 lives by March, according to calculations by the University of Washington's Institute for Health Metrics and Evaluation (IHME).

As of Saturday, nearly 12 million people in the US have been infected with the coronavirus and more than 254,000 have died.

People with no symptoms could drive Thanksgiving infections

Research suggests that asymptomatic people are generally less infectious than those who develop symptoms — they aren't expelling as much of the virus. But the false sense of security that can come with a lack of symptoms can lead those people to be less careful around others. That may be what makes them such significant drivers of the virus's spread.

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A family celebrates Thanksgiving on November 24, 2016 in Stamford, Connecticut. John Moore/Getty

It's unclear just how long asymptomatic people can be infectious. In one case, a 71-year-old hospital patient continued to test positive for the coronavirus — meaning her body still contained traces of the virus' genetic material — for 100 days without developing symptoms.

"We think that at least up to day 70, this patient would have been able to spread the virus to others," Vincent Munster, a virologist at National Institute of Allergy and Infectious Diseases, told Business Insider.

Researchers believe the situation arose because the woman's weakened immune system was unable to mount a substantial defense against the virus. 

In addition, people who do develop symptoms can be infectious before their illness becomes noticeable. In this "pre-symptomatic" stage, the day before you show symptoms can be one of the days you're spewing the most virus.

All of this does not bode well for the holidays.

"You get one person who's asymptomatic and infected, and then all of a sudden four or five people in that gathering are infected," Fauci said last month. "That's the exact scenario that you're going to see in Thanksgiving."

Public-health experts advise keeping Thanksgiving gatherings as small as possible or, if possible, avoiding them entirely. They also suggest moving Thanksgiving outdoors, ensuring good ventilation if you stay indoors, wearing masks when not eating, and getting tested before and after travel.

Susie Neilson contributed to reporting.

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