MRNA Vaccines Efficacious Against Omicron Infections in Children Younger Than 12

Both mRNA (BNT162b2, Pfizer and mRNA-1273, Moderna) COVID-19 vaccines were effective against Omicron (B11529) acute infection and severe disease for children under 12 years of age, according to a new study published in The Lancet Infectious Diseases.

This observational study had 2 cohorts: 5-11 years and 0-4 years of age.

“For children 5–11 years of age, the effectiveness of primary vaccination against infection, compared with being unvaccinated, was 59.9% (95% CI 58.5–61.2) at 1 month, 33·7% (32.6–34.8) at 4 months, and 14.9% (95% CI 12.3–17.5) at 10 months after the first dose,” the investigators wrote. “Compared with primary vaccination only, the effectiveness of a monovalent booster dose after 1 month was 24.4% (14.4–33.2) and that of a bivalent booster dose was 76.7% (45.7–90.0). The effectiveness of omicron infection against reinfection was 79.9% (78.8–80.9) after 3 months and 53.9% (52.3–55.5) after 6 months.”

For younger children, 0-4 years of age, the efficaciousness of the vaccines were similar during the first 2 months to the older children, but the duration of protection was better over time in the younger cohort.

“The effectiveness of primary vaccination against infection, compared with being unvaccinated, was 63.8% (57·0–69·5) at 2 months and 58·1% (48.3–66.1) at 5 months after the first dose, and the effectiveness of omicron infection against reinfection was 77.3% (75.9–78.6) after 3 months and 64.7% (63.3–66.1) after 6 months,” the investigators wrote of the younger cohort.

The authors said vaccination and previous COVID-19 infection had better effectiveness against severe illness for both cohorts.

The Omicron variant emerged in the United States in December 2021, and within a matter of weeks was the dominant strain in the country.

Study Parameters
This was an observational cohort study, looking at children’s mRNA vaccination records and outcomes from the North Carolina COVID-19 Surveillance System and the COVID-19 Vaccine Management System.

This included 1,368,721 state residents aged 11 years or younger. The investigators used the Cox regression to estimate the time-varying effects of primary and booster vaccination and previous infection on the risks of omicron infection, hospital admission, and death.

According to the authors, one of the bigger limitations for this study was the short follow-up period, and that it could not help to determine the long-term understanding of vaccination and previous infection.

The investigators explained the study provided some important data in these age groups where there was a paucity of information. Along with pointing out the effectiveness of both mRNA vaccines in this age group, this study demonstrated bivalent vaccines were more efficacious than monovalent shots and that previous infection increased immunity against future infection.

“…surveillance data are crucially important to our understanding of the protection conferred by vaccination and previous infection in young children,” the authors wrote.