COVID-19 vaccine trial to about 44,000 participants while increasing the diversity of the trial population. The initial target figure for the trial of the covid vaccine that both the companies are jointly developing was up to 30,000 participants, which the companies said they expect to reach by next week.If the study is successful, the companies could submit the vaccine for regulatory approval as early as October, Pfizer 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 companies added in the joint statement on Saturday."The proposed expansion would allow the companies to further increase trial population diversity, and.