Children with no Covid-19 symptoms may shed virus for weeks

Children can shed the novel coronavirus that causes Covid-19, even if they are asymptomatic, or for long after their symptoms have cleared, according to a new study which sheds more light on the significance of the pediatric population in the pandemic's spread.

The study, published in the journal JAMA Pediatrics, followed 91 children at 22 hospitals throughout South Korea, infected with the novel coronavirus SARS-CoV-2, and found that they carried the viral genetic material RNA for a longer period than expected.

"Symptom screening fails to identify most Covid-19 cases in children, and SARS-CoV-2 RNA in children is detected for an unexpectedly long time," the researchers, including those from Seoul National University College of Medicine in South Korea, noted in the study.

In a commentary, published on the study, scientists, including Roberta L. DeBiasi from the The George Washington University School of Medicine and Health Sciences in the US, said children may play an important role in the Covid-19 transmission.

"To our knowledge, no prior studies have systematically focused on the frequency of asymptomatic infection in children or the duration of symptoms and viral shedding in both asymptomatic and symptomatic children," the researchers noted in the commentary.

According to the study, about 22 per cent never developed symptoms, 20 per cent were initially asymptomatic but developed symptoms later, and 58 per cent were symptomatic at their initial test.

Over the course of the research, the scientists said the hospitals where these children stayed continued to test them every three days on average, providing a picture of how long viral shedding continues over time.

The findings revealed that the duration of symptoms varied widely, from three days to nearly three weeks.

The authors of the commentary noted that there was also a significant spread in how long children continued to shed virus and could be potentially infectious.

While the virus was detectable for an average of about two-and-a-half weeks in the entire group, a significant portion of the children -- about a fifth of the asymptomatic patients, and about half of the symptomatic ones -- were still shedding virus at the three-week mark, they said.

The scientists cautioned that children -- a group widely thought to develop mostly mild disease that quickly passes -- can retain symptoms for weeks, and even asymptomatic children continued to shed virus for a long time after initial testing, making them potential key in the transmission of the disease.

However, despite these findings, the commentary noted that a qualitative "positive" or "negative" on testing platforms may not necessarily reflect infectivity.

They explained that some positives may indicate the presence of bits of genetic material that may not be able to make someone sick, or negatives reflecting low levels of virus that may still be infectious.

According to the scientists, testing reliability may be further limited by the testers themselves, with sampling along different portions of the respiratory tract or even by different staff members leading to different laboratory results.

The researchers said it is also unknown whether asymptomatic individuals are shedding different quantities of virus than those with symptoms -- a drawback of the qualitative testing performed by most labs.

Testing only for active virus instead of antibodies ignores the vast number of individuals who may have had and cleared an asymptomatic or mild infection, the scientists added.

"Each of these pieces of information that we, our collaborators and other scientists around the world are working to gather is critical for developing policies that will slow the rate of viral transmission in our community," DeBiasi said.