What you need to know

Multisystem inflammatory syndrome in children (MIS-C) is a rare condition associated with COVID-19. It typically appears two to six weeks after a child develops COVID-19 and involves the inflammation of several different body parts, often including the heart.

A study supported by the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) examined medical records to see how many children hospitalized with COVID-19 had symptoms of MIS-C. The researchers found that as SARS-CoV-2, the virus that causes COVID-19, evolved and spread, smaller percentages of children with COVID-19 were hospitalized for MIS-C. This suggests that the severity of MIS-C symptoms has decreased over time.

What did the researchers do?

The researchers examined records from a database called the International Kawasaki Disease Registry (IKDR), which contains health data from Canada, Egypt, India, Italy, Mexico, Spain, and the United States. The IKDR has collected data on MIS-C and Kawasaki disease — a similar and rare condition affecting young children. Between April 1, 2020, and June 1, 2022, the researchers found that 2,017 pediatric patients hospitalized for COVID-19 met the Centers for Disease Control and Prevention criteria for an MIS-C diagnosis.

The researchers then examined whether mutations to SARS-CoV-2, known as variants, were associated with changes in the severity of illness among these hospitalized MIS-C patients. The team compared the outcomes of patients from early stages of the pandemic — when only the original strain of SARS-CoV-2 was circulating — with outcomes from later periods when virus variants dominated as the leading cause of illness and death.

When the pandemic began, 47% of children with COVID-19 who met the criteria for an MIS-C diagnosis had to be admitted to the intensive care unit (ICU). In the next period, when the Alpha variant was the dominant strain of SARS-CoV-2, nearly 49% of children with MIS-C had to be admitted to the ICU. That percentage then continuously declined. By June of 2022, only 37% of children with MIS-C needed intensive care.

Why is this research important?

Although MIS-C is still a serious health concern for children with COVID-19, as viral variants have evolved and vaccination rates have increased, fewer children who developed the condition have needed the most intensive levels of care for it. This is because MIS-C from these variants and Kawasaki disease have similar symptoms. Future research will help us further understand the differences between the two conditions and refine treatments for them. Research can also examine why SARS-CoV-2 variants appear to cause less severe MIS-C symptoms and how this type of MIS-C compares with other hyper-inflammatory syndromes in children.

Where can I go to learn more?

Symptoms of MIS-C lessened during the pandemic, but still serious

• NICHD shares more details about this study.

When Kids Get Sick After COVID-19 Goes Away

• NIH is following children with MIS-C for five years to understand this COVID-related illness.

Kawasaki Disease

• Kawasaki disease affects children under 5 years of age and causes symptoms similar to MIS-C.

Long COVID: An Uncommon Complication in Children

• Although pediatric cases of Long COVID are relatively uncommon, the condition can affect children, and the symptoms may be different from those in adults.

Sources

McCrindle, B. W., Harahsheh, A. S., Handoko, R., Raghuveer, G., Portman, M. A., Khoury, M., Newburger, J. W., Lee, S., Jain, S. S., Khare, M., Dahdah, N., Manlhiot, C., & the International Kawasaki Disease Registry. (2023). SARS-CoV-2 variants and multisystem inflammatory syndrome in children. New England Journal of Medicine, 388(17), 1624–1626. https://doi.org/10.1056/NEJMc2215074