People who do not have coronavirus symptoms can have just as much virus in their system as those who are hospitalized with COVID-19, and some people carry far higher loads of coronavirus than others, according to two new studies by University of Colorado Boulder researchers.
The studies used data from more than 72,000 saliva samples collected primarily from CU Boulder students and some faculty and staff members between Aug. 17 and Nov. 25 through the campus coronavirus monitoring program.
The studies have not yet been peer reviewed and are in the process of being submitted for publication.
The first study looked at the amount of coronavirus — also known as the viral load — in the samples provided by 1,405 people who tested positive. The research found that half of those who tested positive were in a “non-infectious” phase of the disease because of the low amount of the virus in the sample. Just 2% of those who tested positive carried 90% of the virus, giving credence to the concept of “super-carriers,” and also the potential for super-spreaders. One individual accounted for 5% of the virus measured in the study.
But there are also other variables to consider, said BioFrontiers Institute Director Roy Parker, who collaborated on both projects.
A person’s viral load increases and decreases throughout the infection cycle, so the samples given are a snapshot of that cycle, Parker said. And some people produce far more airborne particles, or aerosols, than others — so they might spread the virus even with a smaller viral load.
The second study found a link between high viral loads in students who tested positive and spread the virus to their roommate. One in five CU Boulder students who tested positive for coronavirus while living with a roommate in the residence halls infected their roommate, and those who transmitted the virus had a viral load that was seven times higher than students who did not spread coronavirus to a roommate.
Finding that only 20% of students passed the virus to their roommates was reassuring, said lead author Kristen Bjorkman, COVID scientific director at the BioFrontiers Institute.
“For a lot of students, having a roommate provides mental health benefits, especially when there’s reduced socialization opportunities these days,” she said.
The studies are also reassurance that the protocols put into place in the fall — including monitoring tests, isolation rooms and contact tracing — were worth the time and investment, Bjorkman said. It also motivated the decision to offer more monitoring tests to students living off-campus.
The research would have surprised Parker back in the fall, he said, because it was the expectation that if one roommate got coronavirus, so would the other.
“We’re learning that not every person is as infectious as the next,” Parker said. “Some folks infect a lot of people, and others infect very few.”
Combined, the studies suggest that people who are super-spreaders of coronavirus could carry high levels of the virus in their systems, though it’s unknown why some people carry higher virus loads than others.
“We knew there was diversity with the viral load, but it was surprising to see how concentrated it could be,” Bjorkman said.
One of the most unique aspects of both studies is that they used samples from people who did not have symptoms at the time they were tested.
“There is not always great acceptance of the fact that asymptomatic people can transmit the virus just as much as symptomatic people,” Bjorkman said.
And when those without symptoms are more likely to be out interacting in the community, that can be a problem.
“You can have a very high viral load and be walking around and feel perfectly fine,” Bjorkman said.
Researchers next want to look at why certain people produce more virus than others, Parker said.
“What we would like to do is understand what is it about people that make lots of virus and those who make less, and can we predict who those are?” Parker said.
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