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Children with no COVID-19 symptoms may be more contagious than sick adults, study finds

Authors of the pediatric study say children may be at increased risk of transmitting the coronavirus even if they show mild or zero symptoms.

A new U.S. study has found children infected with the new coronavirus -- even those with mild or no symptoms -- can have a significantly higher level of the virus in their airways than adult COVID-19 patients in intensive care. That high viral load can increase the risk of transmitting the virus to others, the authors say.

Massachusetts General Hospital (MGH) and Mass General Hospital for Children (MGHfC) say it shows children may play a larger role in community spread than previously thought. It also raises new concerns about the reopening of daycare centers and schools without proper safety measures.

“Kids are not immune from this infection, and their symptoms don’t correlate with exposure and infection,” said study senior author Dr. Alessio Fasano, director of the Mucosal Immunology and Biology Research Center at MGH, in a statement. “We should not discount children as potential spreaders for this virus.”

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The study involved 192 children and young adults ranging in age from zero to 22 years old. Forty-nine tested positive for COVID-19 and 18 others had late-onset illnesses related to COVID-19, according to a statement by MGH. Researchers looked at nose and throat swabs and blood samples.

Data shows that even though young children have fewer immune receptors than older children and adults, they can still carry a high viral load, according to MGH. That means they can be more contagious regardless of their susceptibility to developing COVID-19.

“I was not expecting the viral load to be so high," said Dr. Lael Yonker, lead author of the study and director of the MGH Cystic Fibrosis Center, in a statement. "You think of a hospital, and of all of the precautions taken to treat severely ill adults, but the viral loads of these hospitalized patients are significantly lower than a ‘healthy child’ who is walking around with a high SARS-CoV-2 viral load.”

The fact that some COVID-19 symptoms such as cough, fever and runny nose are similar to other childhood illnesses makes it more difficult to diagnose the virus in children, MGH said.

The study's authors recommend that schools emphasize universal mask use, social distancing, hand washing and a combination of remote and in-person learning. Routine screening of students for COVID-19 is also recommended.

“If schools were to reopen fully without necessary precautions, it is likely that children will play a larger role in this pandemic,” the authors said.

The authors said there was particular concern for lower income families where multiple generations live together. It could increase the risk of children spreading the virus to older adults, such as grandparents.

The study, which MGH said is the most comprehensive study of pediatric COVID-19 patients to date, is published in the peer-reviewed Journal of Pediatrics.

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