MIS-C cases increased last fall, study finds
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Key takeaways:
- Cases of multisystem inflammatory syndrome in children increased last fall.
- Most MIS-C cases occur among children who have not been vaccinated against COVID-19.
Cases of multisystem inflammatory syndrome in children increased by nearly two-thirds last fall, aligning with an increase in COVID-19 activity, according to a study published in MMWR.
The study found that most cases of multisystem inflammatory syndrome in children (MIS-C) occur in children who are not vaccinated against COVID-19.
In 2020, the CDC published an updated definition of MIS-C, which took effect on Jan. 1, 2023. It replaced a definition from 2020 that required “the presence of fever, systemic inflammation using a number of biomarkers, and involvement of at least two of seven organ systems,” the authors of the new study wrote.
The new case definition no longer requires a duration of subjective or measured fever but does require a C-reactive protein (CRP) test result of 3 mg/dL or more to indicate systemic inflammation, among other changes, the authors noted, adding that 87% of cases reported using the 2020 case definition also meet the 2023 case definition.
As of Feb. 26, 2024, there were 117 new cases of MIS-C identified in 2023. Of these patients, 31 experienced onset of the syndrome from August through October, following an increase in COVID-19 activity earlier in the summer — a 63% increase in cases compared with the previous 3 months.
Overall, however, cases of MIS-C have decreased 98% from a peak during October 2020 to April 2021, according to the authors.
Among the 117 MIS-C cases identified in 2023, 58% occurred in previously healthy children with no underlying medical conditions, 50% required ICU-level care, 34% experienced shock and 27% experienced cardiac dysfunction, the researchers found. Three of the children died.
Additionally, although 96% of the patients with MIS-C were eligible for COVID-19 vaccination, only 18% had any documented evidence of being vaccinated. Among the 20 vaccinated children, 12 had received their last dose over 12 months before onset of MIS-C.
Among all 117 patients, 27.4% had obesity, 13.7% had a chronic lung disease such as asthma, 7.7% had a developmental condition, 5.1% had a cardiovascular condition and 1.7% had an immunosuppressive disorder or malignancy.
The authors reiterated the CDC’s recommendation that all eligible children remain up to date with COVID-19 vaccination.
“MIS-C patients with illness onset in 2023 were predominantly unvaccinated children and those whose vaccine-induced immunity had likely waned,” they wrote. “COVID-19 vaccination remains an important tool for preventing MIS-C.”
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