Pfizer (NYSE:PFE) and its partner BioNTech SE (NSDQ:BNTX) aim to expand the recent FDA approval of their COVID-19 vaccine to include booster doses for individuals 16 and older.

The companies have submitted a supplemental Biologics License Application to the FDA, including Phase 3 data drawn from participants aged 15 to 55.

The latest data indicate that a third dose of the Comirnaty vaccine boosts antibody titers and continues to be well tolerated.

Trial investigators administered the booster between 4.8 and 8 months after giving the second dose of the COVID-19 vaccine.

The booster resulted in strong protection against the original or wild-type strain of SARS-CoV-2. Specifically, 99.5% of participants had a four-fold increase in neutralizing antibody levels after the third dose.

The most common side effects were similar to those from earlier doses, including injection-site soreness, fatigue, headache, muscle aches and chills.

The companies had announced on August 16 that they had submitted Phase 1 data to the FDA related to vaccine boosters.

Pfizer and BioNTech also plan to submit the latest data to the European Medicines Agency in the coming weeks.

Not included in the most recent press release was mention of the Delta variant. However, Phase 1 data suggests that a booster dose offers substantially improved protection against Delta, which is now responsible for 98.8% of U.S. infections, according to CDC.

The company is also developing a Delta-specific version of its vaccine and had projected that clinical trials for the modified vaccine would begin this month, subject to regulatory authorization.