The virus that causes COVID-19 can stay in the body for up to two years in some people, according to new research from UC San Francisco.
Scientists found pieces of the virus in the blood of people infected during the first wave of the pandemic up to 14 months after their initial COVID-19 infection and in tissue samples up to two years after the initial infection.
“About 10% of people between three and 14 months after they had COVID had remnants of the virus floating around in their bloodstream,” said Michael Peluso, an infectious disease researcher in the UC San Francisco School of Medicine, who led both studies.
The research offers potential clues as to why some people develop long COVID. It doesn’t mean that 1 in 10 people have viral remnants in their bodies right now.
“These are samples that were largely collected after the first wave of the pandemic when people had no preexisting immunity and vaccines were not available and there were no treatments available,” Peluso said. “We’re now in a totally different era.
“Nearly everyone has had COVID at least once, nearly everyone has some existing immunity,” he added. "We don’t know if this finding would hold up in the present day.”
In California, 5.4% of residents report long COVID symptoms, according to the CDC. It is estimated that up to 20 million Americans are currently grappling with long COVID.
Scientists are finding biological abnormalities, but they aren’t sure what causes long COVID.
One hypothesis is that remnants of the virus, genetic material or proteins, can stick around in the body and create a kind of chronic infection — known as viral persistence.
To investigate that possibility, researchers looked at blood samples from 171 people who had been infected with COVID as far back as 2020. Using an ultra-sensitive test for the COVID "spike” protein, which helps the virus break into human cells, the scientists found the virus was still present up to 14 months later in some people.
People who had been hospitalized with COVID were twice as likely as people with mild cases to have traces of the virus in their bodies. It was also higher for those who reported being sicker, but were not hospitalized.
“We’re currently seeing this in people with long COVID as well as some people who don’t have long COVID symptoms, but it doesn’t mean there aren’t long term consequences,” Peluso said.
“We know that after a person has a COVID infection they are at higher risk for a variety of different medical complications, including heart attacks and strokes,” he added. “The next step in the research is trying to figure out if having pieces of the virus in your body increases the risk of developing long COVID or risk of other medical events after COVID.”
In another study, researchers detected portions of viral RNA for up to two years after infection in the connective tissue where immune cells are located. There was no evidence that the person had become reinfected.
In some samples, the researchers found that the virus could be active.
Peluso said more research is needed to determine whether the persistence of these fragments drives long COVID and associated risks, such as heart attack and stroke. He said he’s also interested in finding out whether the viral fragments are sparking problems with the immune system and creating dysfunction or autoimmunity, in which the body attacks itself.
“It’s equally possible this virus is just inert and isn’t causing harm, but that’s the next question to figure out,” Peluso said. “The best thing a person can do to avoid getting long COVID is not getting COVID in the first place.”
