Pfizer, BioNTech Data Show High COVID-19 Vaccine Efficacy in Children Ages 5 to 11

Data show 99.2% of children 5 to 11 years of age achieved a seroresponse by 1 month after completing the 2-dose vaccine series.

New data released by Pfizer and BioNTech support the companies’ application for FDA authorization of the COVID-19 vaccine in children 5 to 11 years of age, with a relative vaccine efficacy of more than 90%.

According to a briefing document released by the FDA, clinical data investigated a 10-µg vaccine dose in children 5 to 11 years of age, which is one-third of the dose used for adults and children 16 years of age and older. This dose reduction was chosen to reduce adverse effects (AEs), although it still results in a strong immune response.

The brief also noted the significant increase in COVID-19 cases among children over the past several months, especially during the widespread dissemination of the Delta variant. According to a Pfizer press release, researchers have found a 419% increase in COVID-19 cases among children 17 years of age and younger between August and September 2021, compared with June and July 2021.

Furthermore, although the mortality rate for children is significantly lower than mortality in adults, COVID-19 was among the top 10 leading causes of death for children 5 to 14 years of age between January and May 2021 in the United States.

Based on these data and the clinical trial findings, Pfizer and BioNTech are seeking emergency use authorization (EUA) of a 10-µg dose of the vaccine for children 5 to 11 years of age as a 2-dose primary series given 3 weeks apart. The EUA application is supported by safety and efficacy data, as well as a comprehensive Chemistry, Manufacturing, and Controls data package.

Efficacy of the 10-µg dose in children 5 to 11 years of age was inferred based on the immunobridging analysis, which compared SARS-CoV-2 neutralizing antibodies in a subset of participants in this age group with another group of young adult participants 16 to 25 years of age. Among study participants with no prior evidence of SARS-CoV-2 infection up to 1 month after dose 2, the ratio of 50% neutralizing geometric mean titers in children 5 to 11 years of aged compared to individuals 16 to 25 years of age was 1.04.

Furthermore, 99.2% of children 5 to 11 years of age achieved a seroresponse by 1 month after completing the 2-dose vaccine series. There was no difference in proportions of participants who had seroresponses between the 2 age groups.

In addition to these overall findings, geometric mean titers also increased for both the reference and Delta strains after 2 doses of the 10-µg vaccine dose. The titers at 1 month after dose 2 against the reference strain was 365.3, which was approximately 36.5-times the titers found pre-vaccination. Similarly, the titers at 1 month after vaccination for the Delta variant strain was 294.9, which was approximately 29.5-times the titers pre-vaccination.

Safety data were collected from 2250 participants 5 to 11 years of age, including 1518 who received the vaccine and 750 who received the placebo, with a follow-up time of at least 2 months after the second dose. Supplemental safety data were also collected from an expansion group with an additional 2250 participants. At the time of the most recent data cutoff date, the expansion group had a median follow-up time of 2.4 weeks after the second dose.

Reactogenicity was mostly mild to moderate and short-lived, with a median onset of 1 to 4 days after vaccination and resolution within 1 to 2 days after onset. Local reactions presented mostly as injection site pain, although mild to moderate redness and swelling occurred at higher frequencies in children than was previously reported.

Systemic events included fatigue, headache, and muscle pain, and generally increased in frequency or severity with increasing dose number. However, these AEs were typically milder and less frequent than previously reported in earlier studies.


FDA Briefing Document. Vaccines and Related Biological Products Advisory Committee October 26, 2021, Meeting Document. Released October 22, 2021.