Pfizer and BioNTech are looking to expand the enrollment of their Phase 3 COVID-19 vaccine trial to up to approximately 44,000 participants after submitting a proposal to the Food and Drug Administration on Saturday.
According to a press release, the proposed expansion would allow the companies to increase the diversity of the trial's participants, including adolescents as young as 16 years old and people with chronic, stable HIV, Hepatitis C, or Hepatitis B infection, as well as provide additional safety and efficacy data.
The companies noted that the trial is expected to reach its initial enrollment target of up to 30,000 participants by next week.
Pfizer and BioNTech reiterated that results from their vaccine candidate's late-stage trial could be available as early as October.
"The pivotal trial is event-based and there are many variables that will ultimately impact read-out timing, Pfizer and BioNTech said. "As stated previously, based on current infection rates, the companies continue to expect that a conclusive readout on efficacy is likely by the end of October."
The federal government announced in July that it had reached a $1.95 billion agreement with Pfizer and BioNTech for at least 100 million doses following its approval by the FDA. Under the agreement, an additional 500 million doses can be acquired, and U.S. citizens would receive the vaccine for free.
The move came as part of the White House's Operation Warp Speed initiative, which aims to deliver 300 million doses of a safe and effective COVID-19 vaccine by January 2021.
The expansion announcement comes less than a week after the CEOs of the major coronavirus vaccine developers made a joint pledge to avoid applying for FDA approval, even for emergency use, until certain safety and efficacy standards are met.
"We believe this pledge will help ensure public confidence in the rigorous scientific and regulatory process by which COVID-19 vaccines are evaluated and may ultimately be approved," the companies said in the statement.
The joint statement noted that scientific evidence for regulatory approval must come from "large, high quality clinical trials that are randomized and observer-blinded, with an expectation of appropriately designed studies with significant numbers of participants across diverse populations."
Two other vaccine candidates are in late-stage trials, including one made by Moderna Inc. and another made by AstraZeneca and Oxford University.
AstraZeneca and Oxford's vaccine resumed trials on Saturday after being put on hold due to safety concerns. AstraZeneca's chief executive, Pascal Soriot, said this week that despite the pause, the company should still know before the end of the year whether its vaccine candidate is effective against COVID-19.