How Has COVID Viral Shedding Changed Over Time?

Since the pandemic began, researchers have used several metrics to try to track the infectiousness of COVID-19. One mainstay is viral shedding, which is the subject of a new study that aims to determine just how long kids are infectious after being diagnosed with COVID-19.

The study, which was published in JAMA Pediatrics, looked at data from 76 children between the ages of 7 and 18 who tested positive for COVID-19. The researchers took throat swabs during five home visits over 10 days to track viral shedding over time. They determined that most kids were infectious up through day three of their infection, although 18.4% of kids were still infectious on day five. Three kids (or 3.9% of participants) were still infectious on day 10. 

The results raise a lot of questions about viral shedding and where things stand with going back to school or work after having a positive COVID-19 test result. Infectious disease experts explain.

What Is Viral Shedding?

Viral shedding means that a live virus is still detectable for a period of time after someone is infected with an illness, William Schaffner, MD, an infectious disease specialist and professor at the Vanderbilt University School of Medicine, told Verywell.

“Viral shedding suggests that, during the period of time that someone is ‘shedding’ the live virus, that they might be contagious or able to spread the virus to others,” he said. Over time, the amount of virus that people shed drops.

“The way viruses work is that they invade our cells, multiply and then can spread to other cells in the body or to other individuals,” Thomas Russo, MD, a professor and chief of infectious diseases at the University at Buffalo in New York, told Verywell. “People use the term ‘viral shedding’ to talk about when an individual is expelling a virus into the air.”

What Does Viral Shedding Indicate?

In general, viral shedding indicates how potentially infectious someone is—but not all viral shedding can make people around you sick.

“If you shed the virus at low levels, you might not be infectious,” Russo said.

Study coauthor Eran Bendavid, MD, associate professor of medicine at Stanford University, told Verywell that he and his colleagues wanted to help determine how long kids are infectious with COVID-19 after they get sick. But he also said that viral shedding alone is a “poor measure” of how infectious someone is—that’s why his study also looked at viral shedding that also caused evidence of infection in cell cultures.

“Viral shedding is what a PCR test would pick up, and it does not tell you, in isolation, if the virus is capable of causing disease,” Bendavid said. “Why do researchers continue to look at it? Because it’s easy to measure. Infectivity is much more informative but hard to measure. That’s why our study was important.”

How Has COVID Viral Shedding Changed Over Time?

Other data has been collected on different aspects of viral shedding. A study published in Open Forum Infectious Diseases in August 2020 found that people with COVID-19 with higher levels of viral shedding were more likely to be older, have pre-existing chronic conditions, and have more severe forms of the illness than those who shed less of the virus. But it didn’t track the length of time people were infectious.

Another study published in the journal Emerging Infectious Diseases in 2022 found that adults who had the Omicron COVID-19 variant shed the most virus between days two and five after they were diagnosed. The researchers also found that infectious virus was detected up to nine days after people were diagnosed. 

But Schaffner said that there’s no clear information on how viral shedding has changed over the course of the pandemic, given that studies on the virus—including viral shedding—weren’t as robust early on.

“Early in the pandemic, we were using PCR tests, which could detect pieces of the virus,” he said. “Those could have been dead soldiers. Some studies showed that people could be PCR positive for a week, two weeks, and sometimes even longer after they recovered, even though it’s unlikely they were infectious then.”

Bendavid agrees that it’s hard to know how viral shedding has changed over time with the pandemic.

“There are some reasonable implications—for example, that as the disease has become more mild, that shedding has decreased—but we do not actually know that,” Bendavid said. He also pointed out that his study found that children who were unvaccinated—and likely had a more intense illness—shed virus for the same amount of time as those who were vaccinated.

The Centers for Disease Control and Prevention (CDC) currently suggests that people who test positive for COVID-19 isolate until five days after their symptoms started, with isolation ending after someone has been fever-free for 24 hours without the help of medication. However, the CDC also recommends wearing a mask around others through day 10.

Despite the latest study’s findings, Schaffner said that the CDC is unlikely to shorten isolation recommendations around COVID-19.

Russo agrees. “With these findings, nearly one out of five kids going back to school could infect others—but it’s also important to get kids back in school,” he said. “What protocols are we willing to maintain as a functioning society as the risk of COVID goes down, but isn’t zero? We still need to figure that out,” he said.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.