Multisystem Inflammatory Syndrome in Children (MIS-C) Associated with Recent Omicron COVID-19 Subtypes is Rare but Involves Severe Cardiovascular Features.

Multisystem inflammatory syndrome in children (MIS-C) is a rare condition following SARS-CoV2 infection. Prior reports demonstrate that frequency of MIS-C and severity of its cardiovascular findings decreased with the emergence of the Omicron variant at the end of 2021. Recent CDC variants of concern are subtypes of Omicron from the lineage of JN.1, which become the predominant circulating subtype in 1/2024. This single center study compares MIS-C prevalence and its cardiovascular findings in patients who developed MIS-C in 1/2024 or later to those associated with older Omicron subtypes (1/2022 to 12/2024). Six patients were hospitalized with MIS-C from 1/2024 to 4/2025 compared to 26 patients from 1/2022 to 12/2023 (p = 0.01). All six patients of the recent cohort developed left ventricular dysfunction compared with four in the prior cohort (6/6 vs. 4/26, p = 0.0002). Troponin elevation was found in all six of the recent cohort and in 11 of the prior cohort (6/6 vs. 11/26, p = 0.019). Vasodilation requiring vasopressor support occurred in five from the recent cohort and two of the prior cohort (5/6 vs. 2/26, p = 0.016). Two recent cohort patients were supported with venoarterial extracorporeal membrane oxygenation; one died secondary to intractable vasodilation. All surviving patients had complete resolution of the cardiovascular findings within one week. MIS-C appears less common in the current era of COVID-19 Omicron variants but may be associated with more severe cardiovascular manifestations. Despite generally rapid recovery of cardiac function, the severity observed in this cohort highlights the need for continued vigilance.