Pfizer (NYSE:PFE) and BioNTech (Nasdaq:BNTX) announced today that data support a three-dose primary series of their COVID-19 vaccine in young children.

Topline safety, immunogenicity and vaccine efficacy data from a Phase 2/3 trial in young children evaluating a third 3-µg dose of the vaccine — marketed in the U.S. as Comirnaty — showed a strong immune response and a favorable safety profile similar to placebo in children aged six months to under five years old.

In the trial, 1,678 children received a third dose of the vaccine at least two months after second dose, while omicron was the predominant variant. Non-inferiority was met for both the 6-24 month-old population and the 2-under 5-year-old population for both primary endpoints, with the vaccine well tolerated, leading to no new safety signals.

Vaccine efficacy (a secondary endpoint) registered at 80.3% in the analysis, based on 10 symptomatic COVID-19 cases identified from seven days after the third dose and accrued as of April 29, 2022. Final vaccine efficacy data will be shared once available as the trial protocol specifies for a formal analysis when at least 21 cases have accrued from seven days after the third dose.

Pfizer and BioNTech began a rolling FDA emergency use authorization (EUA) submission for the vaccine in Februrary, with a two-dose series determined to be well-tolerated at the time in the young age group. The companies now plan to submit the new data on three doses to the rolling EUA submission this week, followed by submissions around the world after.

“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,” Pfizer Chair and CEO Albert Bourla said in a news release. “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.”

Just last week, the FDA expanded the authorization for the Pfizer-BioNTech COVID-19 vaccine to allow for booster doses in children between the ages of five and 11.