A new study has provided critical data that shows children play a large role in the community spread of COVID-19.

The comprehensive paediatric study, carried out by Massachusetts General Hospital (MGH) and Mass General Hospital for Children (MGHfC), shows that children are silent spreaders of COVID-19, showing higher levels of the virus in their airways that hospitalised adults in ICU needing COVID-19 treatment.

The study examined viral load, immune response, and hyperinflammation in paediatric COVID-19 cases, showing that out of  192 children ages 0-22, 49 children tested positive for the virus, and an additional 18 children had late-onset, COVID-19-related illness. This breakthrough finding challenges the current hypothesis that, because children have lower numbers of immune receptors for COVID-19, this makes them less likely to become infected or seriously ill.

The study, ‘Pediatric SARS-CoV-2: Clinical Presentation, Infectivity, and Immune Reponses’, has been published in the Journal of Pediatrics.

High levels of the virus found in children

The authors say that although younger children have lower numbers of the virus receptor than older children and adults, this does not correlate with a decreased viral load. According to the authors, this finding suggests that children can carry a high viral load, meaning they are more contagious, regardless of their susceptibility to developing a COVID-19 infection.

Risk of contagion is much greater with a high viral load, and, along with viral load, the researchers examined expression of the viral receptor and antibody response in healthy children, children with acute COVID-19, and a smaller number of children with Multisystem Inflammatory Syndrome in Children (MIS-C).

Lael Yonker, MD, director of the MGH Cystic Fibrosis Center and lead author of the study, said: “I was surprised by the high levels of virus we found in children of all ages, especially in the first two days of infection. I was not expecting the viral load to be so high. You think of a hospital, and of all of the precautions taken to treat severely ill adults, but the viral loads of these hospitalised patients are significantly lower than a ‘healthy child’ who is walking around with a high SARS-CoV-2 viral load.”

This raises the risk for the reopening of schools, day care centres, and other locations that have a high density of children and close interaction with teachers and staff members.

“Kids are not immune from this infection, and their symptoms don’t correlate with exposure and infection,” says Alessio Fasano, MD, director of the Mucosal Immunology and Biology Research Center at MGH and senior author of the manuscript. “During this COVID-19 pandemic, we have mainly screened symptomatic subjects, so we have reached the erroneous conclusion that the vast majority of people infected are adults. However, our results show that kids are not protected against this virus. We should not discount children as potential spreaders for this virus.”

The researchers also studied immune response in MIS-C, a multi-organ, systemic infection that can develop in children with COVID-19 several weeks after infection, which can cause severe cardiac problems, shock, and acute heart failure. “This is a severe complication as a result of the immune response to COVID-19 infection, and the number of these patients is growing,” says Fasano, who is also a professor of Paediatrics at Harvard Medical School (HMS). “And, as in adults with these very serious systemic complications, the heart seems to be the favourite organ targeted by post-COVID-19 immune response.”

Early insights into the immune dysfunction in MIS-C should prompt caution when developing vaccine strategies, notes Yonker.

Increasing the risk of community spread

Although children are less likely to become seriously ill, their high viral load means they can carry the virus into their schools and homes, raising concerns for families in socio-economic groups that are disproportionately impacted by the pandemic, including multi-generational families living with vulnerable adults in the same household. For example, in the MGHfC study, 51% of children with acute COVID-19 infection came from low-income communities compared to 2% from high-income communities.

In order to keep children, teachers, and personnel safe, the study recommends not relying on body temperature or symptom monitoring to identify COVID-19 in the school setting.

The researchers emphasise that infection control measures are vital, including social distancing, universal mask use (when implementable), effective hand-washing protocols, and a combination of remote and in-person learning. They consider routine and continued screening of all students for COVID-19, with timely reporting of the results an imperative part of a safe return-to-school policy.