This study describes differences in clinical presentation in hospitalized children with acute COVID-19 and MIS-C between the Delta and Omicron (BA.1.1) waves in a tertiary children’s hospital. This retrospective cohort study with case adjudication of hospitalized children with SARS-CoV-2-positive testing or MIS-C diagnosis occurred during the Delta and Omicron waves, from August 2021 until February 2022. There were no differences noted by race, but both waves disproportionally affected black children (24% and 25%). Assigned by a three-person expert panel, incidental diagnoses were higher in the Omicron wave (34% versus 19%). Hospitalization rates of non-incidental cases were higher during Omicron (3.8 versus 5.9 per 1000 PCR-positive community cases). Respiratory-related admissions were prominent during Delta, while Omicron clinical presentations varied, including a high number of cases of croup and seizures. Length of stay and ICU use during Omicron was significantly less than Delta for MIS-C and acute cases. Estimation of vaccination efficacy for preventing hospital admissions was 85.1–91.7% in the early Omicron period. Our estimates suggest that a protective role for vaccination continues into the Omicron wave. The high rate of incidental cases during the Omicron wave should be considered when reviewing more cursory summative data sets. This study emphasizes the need for continued clinical suspicion of COVID-19 even when lower respiratory symptoms are not dominant.

The etiology and pathogenesis of Kawasaki Disease (KD) remain poorly understood. Amongst the diverse infectious and environmental factors examined to be triggers for, or be associated with KD, are immunizations. In this report, we first describe a Caucasian female who presented with classic KD shortly after receiving her routine 4 month vaccination series. Prior published case reports and large epidemiological studies, which explore potential associations between immunizations and KD and other vasculitides, are then comprehensively reviewed. The methodologic challenges which complicate analysis in this area are also considered. This article is protected by copyright. All rights reserved.

With recent reports showing clinical and laboratory overlap of multisystem inflammatory syndrome in children and Kawasaki disease (KD), we addressed the hypothesis that cross coronavirus humoral immunity leads to a parallel postinfectious phenomenon explaining similar pathologic findings in KD and multisystem inflammatory syndrome in children. We demonstrated no cross-reactivity in children with KD but observed some nonspecific interactions postintravenous immunoglobulin infusion.

Recently, numerous reports have suggested association of pediatric Coronavirus Disease 2019 (COVID-19) cases and Kawasaki Disease (KD). KD is a major cause of childhood acquired heart disease and vasculitis in the pediatric population. Epidemiological patterns suggest KD is related to an infectious agent; however, the etiology remains unknown1. As past reports have considered other coronaviruses to be related to KD2,3, these reports of pediatric COVID-19 related inflammatory disorder cases leads to the hypothesis of potential cross-coronavirus reactivity that would account for the past controversial proposals of other coronaviruses and these new cases. We sought to address this hypothesis by assessing the antigen targeting of biobanked plasma samples of febrile children, including those with KD, against SARS-CoV-2 proteins.