Most children are asymptomatic after confirmed infection with the virus that causes COVID-19, but about one in 1,000 children experience multi-system inflammatory response (MIS-C) for four to six weeks with symptoms including fever, abdominal pain with vomiting and/or diarrhea, rash, and even cardiovascular and neurological problems. If diagnosed early, the condition is readily treatable with immune suppressants such as steroids – left untreated, however, the condition can be fatal.

In an exhaustive analysis by Dr. Carrie Lucas, an assistant professor of immunobiology at Yale University, and colleagues, children with MIS-C were found to have distinct molecules in their blood compared to adults with severe COVID symptoms, as well as healthy children and adults.Specifically, the children with MIS-C had high levels of alarmins, molecules that make up part of the innate immune system which is mobilised quickly to respond to all infections.

“Innate immunity may be more active in children who are infected with virus,” Lucas said. “But on the flip side, in rare cases it may get too revved up and contribute to this inflammatory disease.”

In addition to this children diagnosed with MIS-C were also found to have a marked elevation of certain adaptive immune responses, which are defenses to combat specific, harmful pathogens that typically confer immunological memory. But instead of being protective, the responses produced in these affected children appear to attack a variety of healthy host tissues, a hallmark of autoimmune diseases. This in turn makes the tissue more susceptible to attack by autoantibodies.

Other research findings, meanwhile, have suggested that a child’s innate immune system response may simply be stronger than those of adults, one possible explanation for why they generally experience milder symptoms than adults after infection.

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