MIS-C risk after COVID-19 vaccination falls to one in a million, study finds
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The risk for multisystem inflammatory syndrome in children, or MIS-C, is reduced to just one in a million when a person receives at least one dose of COVID-19 vaccine, researchers reported in The Lancet Child & Adolescent Health.
This is “substantially lower” than the previous estimate of MIS-C among unvaccinated young people in the United States with a confirmed SARS-CoV-2 infection, which was around 200 cases per million, CDC researcher Anna R. Yousaf, MD, and colleagues reported.
“As part of the comprehensive effort to monitor COVID-19 vaccine safety in the United States, CDC has been closely monitoring cases of MIS-C in vaccinated children,” Yousaf said in a press release. “Our results suggest that MIS-C cases following COVID-19 vaccination are rare and that the likelihood of developing MIS-C is much greater in children who are unvaccinated and get COVID-19.”
The CDC defines a case of 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.
Yousaf and colleagues examined data reflecting the first months of COVID-19 vaccine rollout in the U.S., from Dec. 14, 2020, to Aug. 31, 2021, as well 47 reports of potential MIS-C illness that occurred in a person aged 12 to 20 years at any time after a COVID-19 vaccine dose.
Among over 21 million children and adolescents in this age group who received at least one dose of COVID-19 vaccine during the study period, the researchers identified only 21 MIS-C cases, “making the overall reporting rate for MIS-C after vaccination one case per million individuals receiving one or more doses in this age group.”
They separated the cases into those with and without evidence of a past or recent SARS-CoV-2 infection. Of the 21 confirmed cases, 15 (71%) had laboratory evidence of past or recent SARS-CoV-2 infection. The remaining six (29%) did not, a rate of 0.3 cases per million vaccinated individuals.
“As with the individuals in our investigation who had evidence of previous infection outside of the usual period for development of MIS-C, the contribution of vaccination, if any, to the illnesses in individuals without evidence of infection is unknown and cannot be determined with our surveillance data,” they wrote. “It is possible that some of these six individuals had other unrecognized inflammatory conditions.”
In a comment that accompanied the study, Joyce C. Chang MD, MSCE, attending physician in rheumatology at Boston Children’s Hospital, and Mary Beth Son, MD, section chief of rheumatology at Boston Children’s, said the findings “overall are quite reassuring.”
“This timely report is of special interest to health care providers, scientists, and policymakers given ongoing, widespread transmission of the omicron variant,” they wrote.
Unanswered questions remain, however.
“It is unclear whether currently available vaccines will offer similar protection against MIS-C due to different SARS-CoV-2 variants,” they wrote. “Additionally, as the usefulness of serological testing declines among rising rates of seropositivity, we will need better diagnostic tools for MIS-C. The data presented by Yousaf and colleagues show that alternative diagnoses need to be carefully considered among vaccinated children presenting with clinical syndromes mimicking MIS-C.”
References:
Chang JC, Son MBF. Lancet. 2022;doi:10.1016/S2352-4642(22)00061-X.
Yousaf A, et al. Lancet. 2022;doi:10.1016/S2352-4642(22)00028-1.
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