MIS-C across three SARS-CoV-2 variants: Changes in COVID-19 testing and clinical characteristics in a cohort of U.S. children.

As new variants of SARS-Co-V 2 have emerged over time and Omicron sub-variants have become dominant, the severity of illness from COVID-19 has declined despite greater transmissibility. There are fewer data on how the history, diagnosis, and clinical characteristics of multisystem inflammatory syndrome in children (MIS-C) have changed with evolution in SARS-CoV-2 variants. We conducted a retrospective cohort study of patients hospitalized with MIS-C between April 2020 and July 2022 in a tertiary referral center. Patients were sorted into Alpha, Delta, and Omicron variant cohorts by date of admission and using national and regional data on variant prevalence. Among 108 patients with MIS-C, significantly more patients had a documented history of COVID-19 in the two months before MIS-C during Omicron (74%) than during Alpha (42%) (p = 0.03). Platelet count and absolute lymphocyte count were lowest during Omicron, without significant differences in other laboratory tests. However, markers of clinical severity, including percentage with ICU admission, length of ICU stay, use of inotropes, or left ventricular dysfunction, did not differ across variants. This study is limited by its small, single-center case series design and by classification of patients into era of variant by admission date rather than genomic testing of SARS- CoV-2 samples.     Conclusion: Antecedent COVID-19 was more often documented in the Omicron than Alpha or Delta eras, but clinical severity of MIS-C was similar across variant eras. What is Known: • There has been a decrease in incidence of MIS-C in children despite widespread infection with new variants of COVID-19. • Data has varied on if the severity of MIS-C has changed over time across different variant infections. What is New: • MIS-C patients were significantly more likely to report a known prior infection with SARS-CoV-2 during Omicron than during Alpha. • There was no difference in severity of MIS-C between the Alpha, Delta, and Omicron cohorts in our patient population.