TORONTO -- While most children who contract COVID-19 are asymptomatic, those with a multi-system inflammatory response may have more severe reactions to the virus, a new study shows.

Multi-system inflammatory response (MIS-C) is a condition that affects one in 1,000 children and occurs when different parts of the body – including but not limited to the heart, lungs, and skin – become inflamed. Symptoms of the condition can include fevers, abdominal pain, cardiovascular problems, and neurological problems.

The study states that MIS-C can develop and show a response four to six weeks after a child has contracted COVID-19.

In the Yale-led study released last week, blood samples were analyzed from children that have MIS-C and from children who don’t have the condition, as well as samples from adults who have tested positive for COVID-19 and adults who have not contracted the virus. From the analysis, it was discovered that, “children with MIS-C had immune system signatures distinct from other groups.”

The study also stated that children who were diagnosed with MIS-C showed higher levels of alarmins, which are molecules in the immune system that provide an immediate response to infections.

“Innate immunity may be more active in children who are infected with the virus,” Carrie Lucas, assistant professor of immunobiology at Yale University and author of the study, said in the journal. “But on the flip side, in rare cases it may get too revved up and contribute to this inflammatory disease.”

Through the study, Lucas found that children living with MIS-C had immune responses that reacted more aggressively to the virus, and rather than creating protection, the virus would cause the immune system to attack tissues in the body.

With the increase in MIS-C cases during the pandemic, the U.S. Centers for Disease Control and Prevention (CDC) has been tracking the correlation between children who have tested positive for COVID-19 and the development of MIS-C after contracting the virus since May 2020.

As of May 3, 2021, there have been more than 3,700 cases of children in the U.S. who have reported having MIS-C, and 35 deaths relating to the syndrome according to the CDC. Ninety-nine per cent of patients who were diagnosed with MIS-C tested positive for COVID-19, while one per cent was in close contact with someone who had the virus.

The CDC reported that 60 per cent of children with MIS-C are male, and the average age of patients who developed the syndrome was nine years old.

The study says that if MIS-C is identified in the early stages it can be treated, however if left untreated, it could be fatal in children.