Pfizer Inc and BioNTech SE have proposed to the U.S Food and Drug Administration (FDA) to expand the enrollment of their Phase 3 pivotal COVID-19 vaccine trial to up to about 44,000 participants, the companies said on Saturday.

The initial target figure for the trial was up to 30,000 participants, which the companies said they expect to reach by next week.

The proposed expansion would allow the companies to enroll people as young as 16 and people with chronic, stable HIV, hepatitis C and hepatitis B.

"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 companies added in a joint statement.