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Multisystem Inflammatory Syndrome in Children Following the SARS-CoV-2 Delta Variant in Denmark: Clinical Phenotype and Risk by Vaccination Status and Compared to the Pre-Delta COVID-19 Era
20 Pages Posted: 9 Mar 2022
More...Abstract
Background: Multisystem inflammatory syndrome in children (MIS-C) occurs after infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). MIS-C hospitalizations depends on the risk of MIS-C following specific SARS-CoV-2 variants and vaccine effectiveness.
Methods: This prospective nationwide multicentre cohort study included patients aged 0-17 years in Denmark with MIS-C following the SARS-CoV-2 variant Delta in the period August 1, 2021 to February 1, 2022. The risk of MIS-C was calculated using estimated number of infected individuals by vaccination status. We calculated the incidence rate of MIS-C per 1,000,000 vaccinated and unvaccinated person-years and estimated vaccine effectiveness as 1-IRR (incidence rate ratio) using Poisson regression. Phenotype and risk of MIS-C were compared with MIS-C cases from the first year of the pandemic.
Findings: We identified fifty-one MIS-C cases among unvaccinated individuals and one in a fully vaccinated adolescent. The risk of MIS-C was one in 4,000 [95% CI 3,100-5,400] unvaccinated individuals with SARS-CoV-2 variant Delta and one in 15,800 [95% CI 2,800-500,000] vaccinated adolescents with break-through infections. The estimated vaccine effectiveness against MIS-C following the Delta variant was 94% [95% CI; 55%-99%]; p=0·005) in persons aged 5-17 years. The clinical phenotype during the Delta wave was comparable to the pre-Delta era, e.g. hypotension in 57% vs. 50%, respectively.
Interpretation: We found the phenotype and the risk of MIS-C following infection with the Delta variant similar to previous variants. Further, we found a high vaccine effectiveness against MIS-C, which we suggest was due to protection from infection and, possibly, a decreased risk of MIS-C following break-through infection. Knowledge of the risk of MIS-C following different SARS-CoV-2 variants, and the effect of vaccination, is important for estimating MIS-C hospitalizations with new variants, such as Omicron, and in the debate of COVID-19 vaccination of children.
Trial Registration Details: The study was registered at ClinicalTrials.gov (NCT05186597).
Funding Information: The study was funded by a COVID-19 grant from the National Ministry of Higher Education and Science (grant no. 0237-00004B).
Declaration of Interests: None to declare.
Ethics Approval Statement: The study was approved by the Ethics Committee of Capital Region of Denmark (H-20028631) and the Danish Data Protection Agency (P-2019-29). Informed parental consent was provided before participation. A waiver of requirement of informed consent for cases not prospectively enrolled was obtained by the Danish Patient Safety Authority (3-3013-2907/1).
Keywords: Multisystem Inflammatory Syndrome in Children (MIS-C), SARS-CoV-2, variant Delta, incidence, vaccine effectiveness
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