A new large study of children in California shows that unvaccinated kids are at a much higher risk of developing multisystem inflammatory syndrome in children (MIS-C) if they were unvaccinated with two doses of Pfizer's mRNA COVID vaccine before contracting COVID-19.
The protection was significant in all children ages 5 to 17 years, but most notable in children ages 12 to 17, where even one dose of vaccine offered strong protection against developing the severe condition.
MIS-C was first identified in the initial months of the pandemic. Clinically similar to Kawasaki disease or toxic shock syndrome, MIS-C occurs 2 to 8 weeks following COVID-19 infection in a small percentage of children.
"MIS-C is severe, with all children hospitalized, half requiring care in the intensive care unit, and 1–2 % dying," the authors wrote. "However, little is known about the effect of vaccination on the development of MIS-C, especially in the youngest children."
Adolescents most protected
In the study, the authors looked at all MIS-C cases in California reported from January 2, 2021, to June 23, 2022. Vaccination history was linked to MIS-C cases.
A fully vaccinated MIS-C case was defined as a case occurring more than 14 days after the second dose of mRNA vaccine, the authors said.
In total, 133 children with MIS-C (60 aged 5 to 11 and 73 aged 12 to 17 ) were included in the study, though California officials noted another 5 cases of MIS-C in children who were partially vaccinated during the study's time frame.
In the 5- to 11-year-old age-group, 85% of those with MIS-C were unvaccinated, and the incidence rate ratio (IRR) of MIS-C in unvaccinated children was 3.3 (95% confidence interval [CI], 1.6 to 6.7) times higher than in fully vaccinated children.
Among 12- to 17-year-olds, 90% of those with MIS-C were unvaccinated, and the IRR of MIS-C in unvaccinated children was 22.9 times higher (95% CI, 10.5 to 49.8).
When partially vaccinated children—those who received one vaccine dose— were added to the analysis with fully vaccinated children, the IRR of MIS-C among unvaccinated children aged 5 to 11 years was 3.4 times higher (95% CI, 1.7 to 6.6), and in the older age-group it was 16.0 times higher (95% CI, 8.4 to 30.3).
These findings further enforce the importance of vaccinating children against SARS-CoV-2.
"Our results suggest that administration of the Pfizer-BioNTech mRNA SARS-CoV-2 vaccine in children, including those in the younger 5 to 11 years of age cohort, decreased the likelihood of developing MIS-C," the authors concluded. "These findings further enforce the importance of vaccinating children against SARS-CoV-2."
