Multisystem inflammatory syndrome in children (MIS-C) cases by vaccination status in California

Multisystem inflammatory syndrome in children (MIS-C) is a rare condition occurring after SARS-CoV-2 infection in children under 21 years of age. Children (5-17 years) with MIS-C meeting the Centers for Disease Control (CDC) case definition were reported via California's passive disease surveillance system. Incidence of MIS-C was compared in unvaccinated and Pfizer-BioNTech vaccinated children aged 12-17 and 5-11 years. In the 12-17 year-old age group, there were 66 new cases among 872,936 unvaccinated children and 7 new cases among 2,117,575 vaccinated children. In the 5-11 year-old age group, there were 51 new cases among 2,113,725 unvaccinated children and 9 new cases among 1,221,293 vaccinated children. Compared with vaccinated children, the incident rate ratio of MIS-C was higher among unvaccinated children in both the 12-17-year-old group (22.9, 95 % confidence interval [CI]: 10.5-49.8, p < 0.0001) and the 5-11-year-old group (3.3, 95 % CI: 1.6-6.7, p = 0.0004). While MIS-C is rare, our results suggest that vaccination with the Pfizer-BioNTech vaccine is protective against MIS-C.