At the time of our study, our medical group was only vaccinating healthcare workers and patients ≥75 years of age. The 3 patients that were immunized qualified for early vaccination because they either worked or volunteered in a healthcare setting. These cases occurred ≈1 month after the peak surge of COVID-19 cases in Southern California. At the time these patients sought care, only ≈7% of the adult (≥18 years of age) population who were members of the Kaiser Permanente patient group (≈3,776,000 members) had received ≥1 SARS-CoV-2 vaccine, whereas 3 of the 6 patients in this study who had MIS were vaccinated. These 6 patients were hospitalized at 5 of the 15 Kaiser Permanente medical centers across Southern California. We believe the temporal association after SARS-CoV-2 immunization is worth noting, given the theoretical concern of MIS-C/A after vaccination. We did not identify any patients with MIS after vaccination who did not have recent SARS-CoV-2 infection. It is possible that other case-patients in our member population were hospitalized outside of our 15 medical centers and thus were not captured for this case series.
Overall, MIS is rare in adults. In comparison we treated >50 children with MIS-C during January 2021–February 2021 and >100 since May 2020 among a pediatric population of 960,000.
The Centers for Disease Control and Prevention (CDC) allows for vaccination after a SARS-CoV-2 infection after recovery from the acute illness and after the isolation period, with no recommended minimal interval between infection and vaccination. Most cases of MIS-C/A occur 2–6 weeks after an exposure or infection,[1–3] although we have seen several children brought for care as late as 8–10 weeks after a confirmed infection or exposure. We need to continue to monitor for MIS-C/A after SARS-CoV-2 infection and immunization as more of the population are vaccinated, especially as vaccines are administered to children who are at higher risk for MIS. CDC and the US Food and Drug Administration co-manage VAERS (the Vaccine Adverse Event Reporting System), which is being used to monitor for adverse events after COVID-19 vaccines. MIS-C/A is listed as a postvaccination adverse event of special interest and should be reported to VAERS.
Emerging Infectious Diseases. 2021;27(7):1944-1948. © 2021 Centers for Disease Control and Prevention (CDC)