One of the leading COVID-19 vaccine candidates currently in development is getting closer to a potential finish line. Pfizer (NYSE:PFE) said on Wednesday that the recruitment for the crucial U.S. phase 3 clinical trial of its BNT162b2 is more than 50% complete. The company is aiming to recruit 30,000 individuals for the trial.

The news was reported by Pfizer vaccine research and development scientist Dr. Nicholas Kitchin at a meeting of the Centers for Disease Control and Prevention's Advisory Committee on Immunization Practices.

A medical professional writing on a clipboard with a patient in the background

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BNT162b2, which Pfizer is developing in collaboration with Germany's BioNTech (NASDAQ:BNTX), is one of only a handful that is about to advance to phase 3 testing. Enrollment seems to be proceeding quickly; last week, the company said it had recruited over 11,000 individuals. At this pace, enrollment could be complete within only a few more weeks.

The company is confident it can recruit and conduct the late-stage trial quickly and effectively. Pfizer CEO Albert Bourla said in an Aug. 6 interview with The Washington Post that his company could start seeking regulatory approval for BNT162b2 as early as October; that, of course, assumes that the vaccine candidate proves to be efficacious in a relatively fast-moving late-stage trial.

The company has made arrangements with manufacturing partners to make the vaccine, if it is successful in the phase 3 trial and subsequently receives approval from major regulators. In July, Pfizer and BioNTech contracted with the U.S. government to supply up to 600 million doses.

Despite the positive news about BNT162b2, both Pfizer and BioNTech were down in midafternoon trading on Wednesday, in contrast to the gains of the wider market. Pfizer stock was off by 1.1%, while BioNTech had slumped 4.5%. 

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