Effectiveness of monovalent mRNA vaccines against COVID-19 in young children


In a recent report from the CDC, monovalent vaccines from Moderna and Pfizer have shown vaccine effectiveness in children aged 3 to 5 years in at least the first 4 months after vaccination.

Monovalent mRNA vaccines have displayed vaccine effectiveness (VE) in young children aged 3 to 5 years for at least 4 months following vaccination, according to a recent report from the CDC.

Recommendations for the use of the 2-dose monovalent COVID-19 vaccine from Moderna in children aged 6 months to 5 years were issued by the Advisory Committee on Immunization Practices (ACIP) on June 18, 2022. The ACIP also issued recommendations on the 3-dose Monovalent vaccine from Pfizer in this age group.

These recommendations were based on safety and limited efficacy data from clinical trials, with the Increasing Community Access to Testing (ICATT) program used to further determine the efficacy against COVID-19 in children aged 3 years and older. 

Caregivers of minors reported COVID-19 symptoms, infection history, vaccine status, and underlying health conditions at registration to ICATT. Exclusion criteria included being immunocompromised, having a positive COVID-19 test within 3 months, or receiving a non-mRNA vaccine or mixed product regimen.

Nucleic acid amplification tests (NAATs) were performed in participants from August 1, 2022, to February 5, 2023. NAATs of children with 1 or more symptom of COVID-19 were included in the analysis.

The VE of 2 Moderna doses during the ICATT program was 60% from 2 weeks to 2 months after the second dose. From 3 months to 4 months, the VE of the Moderna vaccine decreased to 36%.

The Pfizer vaccine showed a VE of 31% after 3 doses from 2 weeks to 4 months after the third dose. The Moderna vaccine was used in children aged 3 to 5 years, while the Pfizer vaccine was used in children aged 3 to 4 years.

These results indicated protection from COVID-19 for at least 4 months after vaccination. This provided support to the US goal of preventing severe disease and hospitalization.


Fleming-Dutra KE, Ciesla AA, Roper LE, et al. Preliminary estimates of effectiveness of monovalent mRNA vaccines in preventing symptomatic SARS-CoV-2 infection among children aged 3–5 Years — increasing community access to testing program, United States, July 2022–February 2023. MMWR Morb Mortal Wkly Rep. 2023;72:177–182. doi:10.15585/mmwr.mm7207a3

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