, according to a Canadian multicenter cohort study.
The adjusted absolute risk for admission to an intensive care unit was 43.6% among children aged 6 years and older and 46.2% in children aged 13 to 17 years, compared with 18.4% in children aged 5 years or younger.
“We do not understand why teens get more severe MIS-C than younger children,” senior author Joan Robinson, MD, of the University of Alberta, Edmonton, told this news organization. “It is possible that more exposures to other coronaviruses in the past result in them having a more robust immune response to SARS-CoV-2, which results in more inflammation.”
The data were published in the Canadian Medical Association Journal.
A multinational study
The study included data on 232 children admitted with probable or confirmed MIS-C at 15 hospitals in Canada, Iran, and Costa Rica between March 1, 2020, and March 7, 2021. The median age of the children was 5.8 years, 56.0% were boys, and 21.6% had comorbidities.
Although cardiac involvement was common (58.6%), and almost one-third of the cohort (31.5%) was admitted to an ICU, “recovery was typically rapid, with 85% of patients discharged within 10 days,” said Dr. Robinson, for the Pediatric Investigators Collaborative Network on Infections in Canada (PICNIC).
Older age as a risk
The results suggest that older age is associated with increased risk of severe MIS-C. “However, one would then predict that adults would be at even higher risk than teens, whereas the same syndrome in adults (MIS-A) is very, very rare,” said Dr. Robinson.
The study also found that children admitted with ferritin levels greater than 500 μg/L, signaling greater inflammation, also had an increased risk for ICU admission, compared with those with lower levels (adjusted risk difference, 18.4%; relative risk, 1.69). “This is presumably because the more inflammation that the child has, the more likely they are to have inflammation of the heart, which can lead to low blood pressure,” said Dr. Robinson.
Features of MIS-C
Among all patients with MIS-C, gastrointestinal involvement was common (89.2%), as were mucocutaneous findings (84.5%). Children with MIS-C had fever for a median duration of 6 days. “Clinicians who see children in their practice commonly have to determine why a child is febrile. Our study shows that one mainly has to consider MIS-C if febrile children have a rash and one or more of vomiting, diarrhea, or abdominal pain,” said Dr. Robinson.
The study also found that patients with MIS-C who were admitted to the hospital in the latter part of the study period (Nov. 1, 2020, to March 7, 2021) were slightly more likely to require ICU admission, compared with those admitted between March 1 and Oct. 31, 2020. “We cannot provide a clear explanation [for this],” the authors noted. “The features of severe MIS-C were widely publicized by May 2020, so it seems unlikely that severe cases were missed early in the study period. SARS-CoV-2 variants of concern have replaced the wild-type virus. It is possible that the immune response to circulating variants alters the severity of COVID-19 and MIS-C, when compared with wild-type virus.”
Despite initial concerns that pediatric COVID-19 vaccines might cause MIS-C, Dr. Robinson says data suggest this is rarely, if ever, the case, and that vaccines actually prevent the syndrome. She says further studies will be needed to assess MIS-C risk following reinfection with SARS-CoV-2. “I am an optimistic person, and it is my hope that MIS-C following reinfection is rare,” she said. “If this is the case, perhaps we will see very few cases once almost all children have been immunized and/or had SARS-CoV-2 infection.”