medwireNews: The incidence and clinical features of multisystem inflammatory syndrome in children (MIS-C) were similar during the delta wave of COVID-19 to those observed during the first year of the pandemic among unvaccinated children and adolescents, Danish research suggests.
Ulrikka Nygaard (Copenhagen University Hospital) and co-investigators also “found vaccine effectiveness to be high against MIS-C,” which they suggest “was due to protection from infection and, possibly, a decreased incidence of MIS-C after breakthrough infection.”
Nygaard and team identified 52 MIS-C cases, defined according to US Centers for Disease Control and Prevention criteria, that occurred among children and adolescents (<18 years) with COVID-19 in Denmark between August 2021 and February 2022, when the delta variant of SARS-CoV-2 (B.1.617.2 and sublineages) was the dominant strain.
Of these, 51 cases were identified among an estimated 175,458 unvaccinated individuals, giving an estimated incidence of one in 3400.
By comparison, the estimates for MIS-C incidence during the pre-delta COVID-19 era were approximately one in 3000–4000 infections in unvaccinated children and adolescents, the researchers note in The Lancet Child & Adolescent Health.
One MIS-C case occurred following a breakthrough infection in a fully vaccinated adolescent, with a resulting estimated incidence of one in 9900 children and adolescents who had received the Pfizer–BioNTech (BNT162b2) vaccine.
When the investigators only considered the later period of the study (December 2021–February 2022), when vaccination rates had increased, MIS-C incidence was one case in 5500 unvaccinated individuals per year and one case in 87,400 vaccinated adolescents per year, corresponding to an incidence rate ratio of 0.063 and a vaccine effectiveness estimate of 94% against MIS-C.
Nygaard et al also report that the clinical phenotypes of MIS-C were similar during the wild-type and delta waves of COVID-19, with patients during both periods presenting with high rates (>80%) of cardiac, gastrointestinal, and dermatologic involvement.
During the first-wave, 52% of patients with MIS-C required treatment in an intensive care unit, compared with 55% during the delta wave, and there were similar rates of hypotension or shock (57 vs 51%).
During both waves, the patients had a median age of 8 years, there was a similar interval between infection and hospital admission (5.3 vs 5.4 weeks), and there were more cases in boys than girls (61% and 73% boys during wild-type and delta waves, respectively).
The only significant difference between the two time periods was that the median length of hospital stay was longer during the first wave than during the delta wave (8.0 vs 5.0 days), which the team suggests “might partly be explained by prompt use of steroids and anakinra in complicated cases” during delta.
Nygaard and co-authors conclude that their “results highlight that MIS-C remains a rare, but serious, complication of SARS-CoV-2 infection in children and adolescents, and that the phenotype has not changed during the pandemic.”
They add: “Knowledge of the incidence of MIS-C after different SARS-CoV-2 variants and the effect of vaccination might contribute to the elucidation of the extent to which MIS-C is a vaccine-preventable disease.”
medwireNews is an independent medical news service provided by Springer Healthcare Ltd. © 2022 Springer Healthcare Ltd, part of the Springer Nature Group
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Lancet Child Adolesc Health 2022; doi:10.1016/S2352-4642(22)00100-6