Children infected with coronavirus can carry high levels of the virus even when they have few or no symptoms, according to a Massachusetts General Hospital study published Thursday that bolsters growing evidence that kids catch the virus even though they rarely get very sick from it.
Coming as parents and school officials wrestle with whether it’s safe to reopen schools, the study adds fuel to worries that children may spread the virus — but it does not show that they do.
“We cannot be cavalier — ‘OK, the kids are fine,’ ” said Dr. Alessio Fasano, director of Mass. General’s Mucosal Immunology and Biology Research Center and senior author of the study, published in the Journal of Pediatrics.
“If they carry the virus in high numbers in their airways, they can definitely spread the virus around,” he said. “We have to be aware of that when we open the schools.”
But other experts who were not involved in research disputed that conclusion. The test used to detect coronavirus only shows the presence of viral genetic material, not live virus, and it doesn’t indicate how infectious a person is, these critics said.
Dr. Cody Meissner, chief of pediatric infectious diseases at Tufts Medical Center, called the study “slanted” and devoid of new insights.
“No one disputes the fact that children get it,” Meissner said. “You can’t really jump to the supposition that this increases the likelihood that children transmit the virus. We have very solid evidence that that’s not the case. . . . The evidence that children are important vectors is simply not there.”
In contrast, Dr. Mark R. Schleiss, a pediatric infectious diseases specialist at University of Minnesota Medical School, called the study “very useful” and “nicely done,” confirming other recent research about “the importance of children in the dissemination and spread of COVID-19.”
Schleiss said it is “biologically plausible” that children with high viral loads would transmit the illness.
The hospital initiated the study to understand why children had seemingly been spared from COVID-19, Fasano said. Instead, researchers found that in fact many had been infected but had no symptoms at all, or mild symptoms hard to distinguish from colds or allergies. As a result children weren’t being tested for the virus.
The study enrolled 192 young people up to age 22 considered at risk for COVID-19 because they had symptoms, had been in contact with an infected person, or lived in a “hot spot” with high rates of infection, such as Chelsea or Revere. The participants provided samples of blood, urine, saliva, and swabs from the nose and mouth for Mass. General’s COVID-19 Biorepository.
About a quarter of the participants — 49 — tested positive for the coronavirus, and all had high amounts of the virus in their noses, although there was no correlation between the amount of virus detected and the severity of symptoms. On average, their viral load was higher than found in adults sick enough to be hospitalized.
“The fact that you have high viral load in your nose and you are sneezing around, you are transmitting the virus,” Fasano said. “They are potential spreaders. This is based on years and years of experience of many other viral infections.”
Fasano advises that schools decrease the density of classrooms and require mask-wearing and frequent hand hygiene.
The findings are not entirely new. A small study published in late July had also found that children have coronavirus in their noses and throats at levels similar to adults. The lead author of that study, Dr. Taylor Heald-Sargent, a pediatric infectious diseases expert at the Ann and Robert H. Lurie Children’s Hospital of Chicago, said the Mass. General study “adds to the growing body of evidence that we need to be careful around children and not assume that they cannot spread the virus.”
But Dr. William V. Raszka, Jr., a pediatric infectious disease specialist at the University of Vermont’s Larner College of Medicine, said the study does nothing to change his thinking. Raszka recently coauthored a commentary saying that children rarely transmit COVID-19, which appeared in another journal, Pediatrics, where he is associate editor.
“Just because you find virus in the nose doesn’t mean children are infectious,” he said. “This article can’t say anything about whether or not children can rarely or frequently transmit the virus.”
The study has no information about where children acquired their infection, and other studies of household contacts suggest that children get infected by adults rather than the other way around, Raszka said.
Dr. Silvia S. Chiang, a pediatric infectious diseases physician at Rhode Island Hospital and assistant professor of pediatrics at Brown University’s Warren Alpert Medical School, agreed that a high viral load doesn’t necessarily mean that someone will transmit the virus.
“You have to get the virus out of your nose into somebody else’s nose. It’s possible that kids don’t cough, sneeze, or talk with as much force as adults,” she said.
Still, Chiang said, the Mass. General data are “certainly not reassuring.” Based on other studies, she said, she believes adolescents may transmit the virus but younger children may not spread it as easily — “but I want to see more data.”
Most of the 49 children who tested positive in the Mass. General study were older than 11.
Fasano acknowledged that a key limitation of his study is that it involves a small sample.
“I’m pretty sure a paper like this will give the impetus for colleagues to look for COVID-19 infection in kids in a more careful way and not brush it off as an issue that does not involve kids,” he said.
The research was supported by the National Institutes of Health, the Cystic Fibrosis Foundation, the Centers for Disease Control and Prevention, Massachusetts General Hospital, and private donors.
This story has been updated to clarify comments from Dr. Silvia Chiang.