Coronavirus vaccine (illustrative)
Coronavirus vaccine (illustrative) Olivier Fitoussi/Flash90

Pfizer Inc. (NYSE: PFE) and BioNTech SE (Nasdaq: BNTX) on Monday announced topline safety, immunogenicity and vaccine efficacy data from a Phase 2/3 trial evaluating a third 3-µg dose of the Pfizer-BioNTech COVID-19 vaccine in children six months to under five years of age. Following a third dose in this age group, the vaccine was found to elicit a strong immune response, with a favorable safety profile similar to placebo.

Vaccine efficacy, a secondary endpoint in this trial, was 80.3% in children 6 months to under 5 years of age. This descriptive analysis was based on 10 symptomatic COVID-19 cases identified from seven days after the third dose and accrued as of April 29, 2022. The trial protocol specifies a formal analysis will be performed when at least 21 cases have accrued from seven days after the third dose. Final vaccine efficacy data will be shared once available.

“Our COVID-19 vaccine has been studied in thousands of children and adolescents, and we are pleased that our formulation for the youngest children, which we carefully selected to be one-tenth of the dose strength for adults, was well tolerated and produced a strong immune response,” said Albert Bourla, Chairman and Chief Executive Officer of Pfizer.

“These topline safety, immunogenicity and efficacy data are encouraging, and we look forward to soon completing our submissions to regulators globally with the hope of making this vaccine available to younger children as quickly as possible, subject to regulatory authorization.”

“The study suggests that a low 3-ug dose of our vaccine, carefully selected based on tolerability data, provides young children with a high level of protection against the recent COVID-19 strains,” said Prof. Ugur Sahin, M.D., CEO and co-founder of BioNTech. “We are preparing the relevant documents and expect completing the submission process to the FDA this week, with submissions to EMA and other regulatory agencies to follow within the coming weeks.”

In the Phase 2/3 trial, 1,678 children received a third dose of the 3-µg formulation at least two months after the second dose at a time when Omicron was the predominant variant. The immunogenicity analysis of geometric mean titer (GMT) ratio and seroresponse rate was conducted on a subset of study participants one month following the third dose in children 6 months to under 5 years of age, compared to the second dose in the 16- to 25-year-old population. Non-inferiority was met for both the 6- to 24-month-old population and the 2- to under 5-year-old population for both co-primary endpoints. Three 3-µg doses of the Pfizer-BioNTech COVID-19 vaccine was well-tolerated in this age group, and no new safety signals were identified. The majority of adverse events were mild or moderate.

Studies in adults, adolescents, and children over 5 years of age continue to indicate that three doses of the Pfizer-BioNTech COVID-19 vaccine enhances protection compared to two doses. The safety, immunogenicity and vaccine efficacy data for three doses of the vaccine in children under 5 years of age are consistent with the data seen in adults, suggesting that a third dose will provide similar benefit in children.

In February 2022, the companies initiated a rolling submission for Emergency Use Authorization (EUA) of their COVID-19 vaccine in children 6 months to under 5 years of age, following a request by the US Food and Drug Administration (FDA). At that time, a two-dose series was determined to be well-tolerated in this age group. Pfizer and BioNTech plan to submit these new safety, immunogenicity, and vaccine efficacy data on three doses to the rolling US EUA application this week, with submissions to regulators worldwide to follow.

The Phase 1/2/3 trial has enrolled more than 10,000 children ages 6 months to under 12 years of age in the United States, Finland, Poland, and Spain from more than 90 clinical trial sites. The trial evaluated the safety, tolerability, and immunogenicity of three doses of the Pfizer-BioNTech COVID-19 vaccine in three age groups: ages 5 to under 12 years; ages 2 to under 5 years; and ages 6 months to under 2 years. Based on the Phase 1 dose-escalation portion of the trial, children ages 5 to under 12 years received a two-dose schedule of 10 µg each while children under age 5 received a lower 3 µg dose for each injection in the Phase 2/3 study. The trial enrolled children with or without prior evidence of SARS-CoV-2 infection.