MIS-C in 2023: Rarer Than Early in the Pandemic, Mostly in Unvaccinated Children

Multisystem inflammatory syndrome in children (MIS-C) is a rare but serious condition that usually appears 2–6 weeks after a SARS-CoV-2 infection, with fever and inflammation affecting several organs. CDC began national surveillance in May 2020, with state and local health departments reporting cases voluntarily; a new case definition, written with the Council of State and Territorial Epidemiologists (CSTE), took effect on January 1, 2023 (about 87% of cases under the old definition also meet the new one).

Image from CDC's report

Far fewer cases — but not none

117 children and young people had MIS-C starting in 2023. After COVID-19 rose in early summer, 31 cases (26%) began in August–October — about two-thirds more than the 19 in the three months before.

Who got sick

How sick they were

Three patients (3%) died in 2023. Most patients had gastrointestinal (88.9%) and skin or mucous-membrane (88.9%) involvement, and more than half had heart (53.8%) or blood (53.8%) involvement. Most were treated with intravenous immunoglobulin (85.5%) and steroids (80.3%); the median hospital stay was 4 days.

Vaccination

Of the 112 patients old enough to be vaccinated:

• 92 (82.1%) had no COVID-19 vaccine;
• only 20 (18%) had any dose — and 12 of those 20 (60%) had their last dose more than 12 months before falling ill, so their protection had likely waned;
• among the 48 eligible patients with an underlying condition, just 9 (19%) were vaccinated.

What it means

• MIS-C is still happening, if far less often — and the 2023 figures are probably an undercount, since reporting is incomplete and the case definition changed that year. The drop may also reflect immunity from vaccination and past infection and the traits of the variants now circulating.
• Cases have shifted toward younger children, and the illness's features have changed.
• Clinicians should keep MIS-C in mind, especially during and after COVID-19 surges, and know the treatment guidelines.
• Keep reporting cases to health departments.
• CDC recommends that everyone 6 months and older stay up to date with COVID-19 vaccination, to protect against severe illness and complications including MIS-C.

Sources

Based on Anna R. Yousaf, Katherine N. Lindsey, Michael J. Wu, Ami B. Shah, Rebecca J. Free, Regina M. Simeone, Laura D. Zambrano, Angela P. Campbell and the MIS-C Surveillance Authorship Group, "Notes from the Field: Surveillance for Multisystem Inflammatory Syndrome in Children — United States, 2023," MMWR, volume 73, Centers for Disease Control and Prevention; a work of the United States government in the public domain.