The vaccine was estimated to be 91% effective in preventing Multisystem Inflammatory Syndrome in Children (MIS-C) in 12- to 18-year-olds, the study said. MIS-C causes inflammation in children in organs including the heart, lungs, kidneys and brain two to six weeks after a mild or asymptomatic infection.

The estimate is based on the assessment of 283 hospitalized patients aged 12-18 years at 24 children's hospitals in 20 states between July and early December, when the prevalence of the Delta coronavirus variant was high.

All 38 MIS-C patients requiring life support were unvaccinated, the study said.

The results add to a growing body of evidence that vaccination against COVID-19 is likely to prevent disease-related complications in children, including MIS-C, the report said. It was not previously known whether the Pfizer/BioNTech vaccine prevented the condition.

The study's findings have several limitations including questions about vaccine effectiveness against the fast-spreading Omicron variant, the report published in the CDC's Mortality and Morbidity Weekly Report (MMWR) said.

Children aged 5-11 years are at highest risk for MIS-C but only became eligible for the Pfizer-BioNTech vaccine in late October in the United States. They were not included in the analysis, the report said.

(Reporting by Manojna Maddipatla in Bengaluru; Editing by Cynthia Osterman)