CDC evaluation of the efficacy of monovalent mRNA vaccines in preventing symptomatic SARS-CoV-2 infection in 3 to 5-year-olds

In a recent study published in the Morbidity and Mortality Weekly Report by the United States Centers for Disease Control and Prevention (CDC), researchers estimate the efficacy of the monovalent messenger ribonucleic acid (mRNA) coronavirus disease 2019 (COVID-19) in preventing symptomatic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections in the pediatric population between the ages of three and five.

Study: 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. Image Credit: Yuganov Konstantin / Shutterstock.com

Background

Although early vaccination efforts were focused on the elderly and at-risk populations, the Advisory Committee on Immunization Practices (ACIP) approved a two-dose regimen of the monovalent mRNA COVID-19 vaccine by Moderna, and a three-dose regimen on the Pfizer-BioNTech monovalent mRNA vaccine, as primary vaccinations for children between the ages of six months and four years in July 2022. Both monovalent mRNA vaccines were approved based on immunobridging, safety, and efficacy data obtained from clinical trials.

About the study

In the present study, data from the Increasing Community Access to Testing (ICATT) program, through which SARS-CoV-2 tests are administered at no cost to individuals above the age of three at community-based testing centers and pharmacies across the U.S., were used to estimate vaccine efficacies.

At these testing points, caregivers or parents of children reported previous SARS-CoV-2 infections, COVID-19-like symptoms, and other underlying health conditions during registration. Vaccination histories of the children, such as the total number of vaccine doses received, the type of vaccine and manufacturer information, as well as the date of the most recent dose, were also collected at these centers.

The results of nucleic acid amplification tests (NAAT) from children with COVID-19-like symptoms were included in a case-control study with a test-negative design.

NAAT results from children were excluded if the caregivers reported an immunocompromised condition or positive SARS-CoV-2 tests in the last three months or if the child had received a non-mRNA or mixed regimen of the COVID-19 vaccine. Any child who had received a vaccine dose in the two weeks leading up to the test date or had received the third vaccine dose in or after December 2022, when bivalent vaccines were being administered to children between the ages of three and five was also excluded from the study.

Vaccine efficacy was evaluated using comparisons of COVID-19 vaccinations and unvaccinated cases among patients with positive SARS-CoV-2 test results and a control group comprising children with negative SARS-CoV-2 tests. This data was stratified based on the number of doses and type of vaccine.

Results

The effectiveness of the primary regimen comprising two doses of the Moderna monovalent mRNA vaccine against symptomatic SARS-CoV-2 infections among children between the ages of three and five was 60% after two weeks to two months from the second dose. This vaccine efficacy decreased to 36% between three and four months from the second dose.

Receipt of three doses of the Pfizer-BioNTech monovalent mRNA vaccine was 31% effective between two weeks to four months after the third dose among three- and four-year-old children.

Thus, complete primary vaccination with the Moderna and Pfizer-BioNTech monovalent mRNA vaccines for children aged three to five and three to four, respectively, was effective in protecting against symptomatic COVID-19 for at least four months after vaccination.

The efficacy of a single monovalent Moderna mRNA COVID-19 vaccine dose was 40% two weeks to one month after the first dose. The efficacy of the Pfizer-BioNTech monovalent mRNA vaccine was 19% between two weeks and one month after the first dose and 40% two weeks to three months after the second dose.

While the data for vaccination efficacy against severe SARS-CoV-2 infections in children is not yet available, these results provide insights into the effectiveness of COVID-19 mRNA vaccines against symptomatic infections. Furthermore, in general, COVID-19 mRNA vaccines have shown higher effectiveness against severe COVID-19 than against symptomatic infections.

The study findings suggest that vaccine effectiveness against symptomatic infection among children between the ages of three and five wanes around three to four months after the second dose of the Moderna monovalent mRNA vaccine, which is similar to what has been observed among adults and older children. While time-stratified data for the Pfizer-BioNTech monovalent mRNA vaccine was not available for the study, the waning of vaccine efficacy is thought to follow the same pattern as that of the Moderna vaccine.

The U.S. CDC has recommended a third dose of the bivalent mRNA vaccine as of December 2022 for children between the ages of six months and four years. Bivalent COVID-19 vaccines have shown increased efficacy against infection with the emergent Omicron variants and severe COVID-19 and hospitalization among adults.

Conclusions

The complete primary series of the Pfizer-BioNTech and Moderna monovalent mRNA vaccines was found to protect children aged three to five against symptomatic SARS-CoV-2 infections for up to four months, after which immunity begins to wane.

The U.S. CDC recommends a booster dose of the bivalent mRNA vaccine for children between six months and five years of age to mitigate this waning immunity and protect against emergent Omicron variants.