MIS-C risk during omicron substantially lower than previous waves
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The risk for multisystem inflammatory syndrome in children after infection with SARS-CoV-2 was substantially lower during the omicron wave compared with other variants, researchers from Denmark reported in JAMA Pediatrics.
The CDC defines a case of multisystem inflammatory syndrome in children (MIS-C) as any patient aged younger than 21 years who presents with a fever; laboratory evidence of inflammation; evidence of clinically severe illness requiring hospitalization, with two or more organs involved, who has no alternative plausible diagnosis and has tested positive for current or recent SARS-CoV-2 infection; or reports exposure to a suspected or confirmed case of COVID-19.
At its peak, the previous estimate of MIS-C among unvaccinated young people in the U.S. was 200 cases per million. Researchers in The Lancet Child & Adolescent Health earlier this year reported that the risk for MIS-C is reduced to one in a million when a person receives at least one dose of COVID-19 vaccine.
Researchers examined 583,618 children and adolescents infected with SARS-CoV-2 from Jan. 1 to March 15, 2022, when omicron caused more than 95% of SRS-CoV-2 infections, including about 267,086 who were vaccinated against COVID-19. They identified one vaccinated and 11 unvaccinated patients with MIS-C, and no cases among the 31,516 estimated individuals reinfected.
Ultimately, the researchers determined that the risk for MIS-C among unvaccinated individuals during the omicron wave was significantly lower than during the delta wave (RR = 0.12; 95% CI, 0.06-0.23).
“This could be explained by a reduced ability of omicron to trigger hyperinflammation as it is phylogenetically different and associated with an increased immune escape,” they wrote. “The lower risk could also partly be explained by a reduced risk after reinfection, although only 6% of our included infected individuals had confirmed reinfection, and such a reduced risk after reinfection has not yet been reported.”
References:
Yousaf A, et al. Lancet. 2022;doi:10.1016/S2352-4642(22)00028-1.