2% Of People Spread 90% Of Coronavirus, CU Boulder Reports Show

BOULDER, CO — Only a few people are responsible for the majority of coronavirus transmissions, according to two reports released Monday from the University of Colorado Boulder.

“The takeaway from these studies is that most people with COVID don’t get other people sick, but a few people get a lot of people sick,” said Sara Sawyer, a CU Boulder professor of molecular, cellular and developmental biology and senior author of the first study.

“If you don’t have a viral supercarrier sitting near you at dinner, you might be OK. But if you do, you’re out of luck. It’s a game of roulette, so you have to continue to be careful.”

The studies also revealed that half of those infected with the virus aren't contagious at the time of their diagnosis, researchers said.

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Researchers analyzed 72,000 test samples for the first study, university officials said.

A person's "viral load" — the amount of virus particles a person carries — drives contagion, the second CU Boulder study shows.

The two studies are among the largest to analyze trends in asymptomatic people. Researchers looked at saliva samples collected from students, faculty and staff on the CU Boulder campus between Aug. 17 and Nov. 25.

“What is so special about these samples is that they are all from infected people with no symptoms — a snapshot of all these seemingly healthy people you assume it is safe to be around,” Sawyer said.

Just 2 percent of those who tested positive in the samples carried 90 percent of the virus. One student with the highest load carried 5 percent, researchers said.

The research shows that it may be important to encourage those with high viral loads to isolate quickly.

Neither paper has been published in a peer-reviewed journal yet.