Original mRNA COVID vaccines protect young kids against Omicron, but efficacy wanes


Center for Infectious Disease Research and Policy

By Jim Wappes

Omicron infection for US children 3 to 5 years old, but it is considerably higher 1 to 2 months after vaccination compared with 3 to 4 months, according to a study today in Morbidity and Mortality Weekly Report.

The Centers for Disease Control and Prevention’s (CDC’s) Advisory Committee on Immunization Practices recommended on June 18, 2022, that children 6 months to 5 years old receive either two doses of the Moderna or three doses of the Pfizer-BioNTech vaccine as a complete series. Both were monovalent (single-strain) vaccines, as the new bivalent (two-strain) booster that contains an Omicron variant component was not yet available.

For the study, CDC researchers assessed vaccine efficacy from July 2022 through February 2023, when the Omicron variant was predominant. The Moderna group comprised kids 3 to 5 years old, while Pfizer recipients were 3 to 4 years old.

From 60% protection early on to 36%

The Moderna group received a nucleic acid amplification test (NAAT) from August 1, 2022, through February 5, 2023. In that group, vaccine effectiveness (VE) against symptomatic Omicron infection was 60% (95% confidence interval [CI], 49% to 68%) 2 weeks to 2 months after the second dose and 36% (95% CI, 15% to 52%) 3 to 4 months after the second dose.

Children receiving the Pfizer vaccine were tested with a NAAT from September 9, 2022, to February 5, 2023. VE of three doses against symptomatic Omicron was 31% (95% CI, 7% to 49%) from 2 weeks to 4 months after receipt of the third dose. Both groups also included unvaccinated same-aged children.

Those who are eligible should receive a bivalent vaccine dose.

The authors conclude, “Children should stay up to date with COVID-19 vaccines, including completing the primary series; those who are eligible should receive a bivalent vaccine dose.” The CDC expanded its recommendations for the use of bivalent vaccines to children aged 6 months or older on December 9, 2022.