How Effective Are COVID-19 Vaccines in Children Younger Than 12?

A large observational cohort study in North Carolina provided valuable information about the benefits of COVID-19 vaccines in children younger than 12. Find out which age group had the most protection from the vaccine and what was the effect of vaccinating children who had previously been infected with SARS-CoV-2.

CHAPEL HILL, NC – COVID-19 vaccination provides a better cross-variant protective immune response than infection alone in children under the age of 12, although the effectiveness was higher in those younger than age 5 compared to those who were 5-11, according to a new study of nearly 1.4 million children in North Carolina.

University of North Carolina Chapel Hill said they conducted the observational cohort study because “data on the protection conferred by COVID-19 vaccination and previous SARS-CoV-2 infection against omicron (B.1.1.529) infection in young children are scarce.” Resultswere published in The Lancet Infectious Diseases.

Other important findings reported by the authors include that:

  • Vaccination was effective against omicron infection and severe illness (hospital admission or death as composite endpoint), although the effectiveness waned over time.
  • Both the mRNA-1273 and BNT162b2 vaccines were effective.
  • Bivalent boosters were more effective than monovalent boosters.
  • Previous SARS-CoV-2 infection induced strong immunity against future infection, although the immunity waned gradually over time.
  • Vaccination provided additional protection for previously infected children, and omicron infection induced strong immunity in both vaccinated and unvaccinated children.

The study team obtained individual-level records on vaccination with the BNT162b2 and mRNA-1273 vaccines and clinical outcomes from the North Carolina COVID-19 Surveillance System and the COVID-19 Vaccine Management System for 1,368, 721 North Carolina residents aged 11 years or younger from Oct 29, 2021 (Oct 29, 2021, for children aged 5–11 years and June 17, 2022 for children aged 0–4 years), to Jan 6, 2023.

Results indicate that, 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. “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.”

On the other hand, for children 0–4 years of age, 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.

“For both age groups, vaccination and previous infection had better effectiveness against severe illness as measured by hospital admission or death as a composite endpoint than against infection,” the authors advise.

The researchers point out that their findings “can be used to develop effective prevention strategies against COVID-19 in children younger than 12 years.”