Pfizer Vaccine Efficacy Against Omicron in Children 5-11 Years

The Omicron variant led to COVID-19 infections spiking in young children. As such, it is necessary to determine whether children are adequately protected by COVID-19 vaccination.

The highly infectious Omicron strain has since continued to mutate, retaining its status as the predominant COVID-19 variant. A study published in The New England Journal of Medicine, investigators determined the real-world effectiveness of the Pfizer-BioNTech (BNT162b2) vaccine against Omicron infection in children 5-11 years of age.

The investigators utilized available data from the largest healthcare organization in Israel. They identified a study cohort of children aged 5-11 years who were vaccinated on or after November 23, 2021. The children were matched with unvaccinated controls to compare vaccine efficacy during the Omicron wave.

After the first and second Pfizer-BioNTech doses, the investigators documented vaccine effectiveness against SARS-CoV-2 infection and symptomatic COVID-19 disease. The study ran until January 7, 2022, after which the cumulative incidence of these 2 outcomes of interest was determined with a Kaplan-Meier estimator. Vaccine effectiveness was calculated as 1 minus the risk ratio, and was also estimated in age subgroups.

A total of 136127 vaccinated children were included in the study cohort, and they were matched with 94728 unvaccinated controls. At 14-27 days after the first dose of Pfizer-BioNTech, estimated vaccine efficacy against documented COVID-19 infection was 17% (95% confidence interval [CI], 7 to 25). A7 7-21 days after the second dose, vaccine efficacy was estimated to be 51% (95% CI, 39 to 61).

Estimated vaccine effectiveness against symptomatic COVID-19 infection was 18% (95% CI, −2 to 34) at 14-27 days after the first dose of Pfizer-BioNTech, and 48% (95% CI, 29 to 63) at 7-21 days after the second dose.

The investigators noted that vaccine efficacy was higher in the younger children, such as those 5-6 and 7-9 years of age. Among the oldest children in the cohort, those 10-11 years, vaccine efficacy was lowest.

This study was conducted right as Omicron was becoming the dominant variant and causing unprecedented rates of COVID-19 in children, including severe and even fatal infection. These findings suggest 2 doses of the Pfizer-BioNTech mRNA vaccine were moderately protective against documented and symptomatic COVID-19 infection in children 5-11 years of age.

More research is certainly merited to determine whether other COVID-19 vaccines or alternative dosages would prove more effective in young children.