By Ethan Covey
While the incidence of multisystem inflammatory syndrome in children (MIS-C) has fallen since the early days of the COVID-19 pandemic, cases of the rare condition are still occurring, particularly in unvaccinated children (MMWR Morb Mortal Wkly Rep 2024;73[10]:225-228).
“Although MIS-C cases have greatly decreased since the start of the pandemic, they are still being reported,” said Anna Yousaf, MD, a CDC medical officer and lead author of the report. “Most cases of MIS-C in 2023 occurred in unvaccinated children and children whose immunity from prior vaccination had declined over time.
“The best way to prevent MIS-C is by staying up to date with COVID-19 vaccines and taking other preventive actions to protect against SARS-CoV-2 infection,” Dr. Yousaf continued.
The investigation focused on all cases of MIS-C with illness onset during 2023, which were reported to CDC national surveillance as of Feb. 26, 2024.
A total of 117 cases were identified. The overall incidence of MIS-C during 2023 was 0.11 cases per 1 million person-months, which represented an 80% decline compared with that of April through December 2022, and a 98% decrease from the peak of 6.79, which was observed early in the pandemic.
Twenty-six percent of the 2023 cases had illness onset during August through October 2023.
“There was a relative increase in monthly reported MIS-C cases in the fall of 2023 following a period of increased COVID-19 activity,” Dr. Yousaf said. “To better understand MIS-C, investigators looked at cases in 2023 and compared them with cases from earlier in the pandemic. Among the children with MIS-C in 2023, 50% required ICU-level care, 34% experienced shock and 27% had decreased heart function.
“These findings are improved compared with cases from 2020-2021 when 63% of children with MIS-C required ICU-level care, 45% had shock and 31% had decreased heart function,” Dr. Yousaf added.
During 2023, 93% of MIS-C cases occurred among unvaccinated children or those whose immunity from prior vaccination had decreased over time.
“Although 96% of children with MIS-C in 2023 were eligible to receive a COVID-19 vaccine two months or more prior to their MIS-C illness, only 18% received any vaccine dose,” Dr. Yousaf said. “Of these vaccinated children, 60% received their last dose more than 12 months prior to MIS-C onset.”
The findings of the report highlight the continued importance of surveillance for MIS-C as well as COVID-19 vaccination for all eligible individuals.
“Parents, healthcare providers and public health practitioners should be aware that although reported MIS-C cases have decreased since 2020, they are still being reported,” Dr. Yousaf said. “Clinicians should recognize that MIS-C might occur especially during and after periods of increased COVID-19 activity and should be familiar with treatment guidelines. Clinicians and public health practitioners should be aware of the 2023 Council of State and Territorial Epidemiologists and CDC MIS-C surveillance case definition.
“The best way to prevent MIS-C is by staying up to date with COVID-19 vaccines and taking other preventive actions to protect against SARS-CoV-2 infection and other respiratory virus infections,” Dr. Yousaf concluded.
Dr. Yousaf reported no relevant financial disclosures.
