Pfizer and BioNTech are moving to enlarge the Phase 3 trial of their Covid-19 vaccine by 50%, which could allow the companies to collect more safety and efficacy data and to increase the diversity of the study’s participants.
The companies said in a press release that they would increase the size of the study to 44,000 participants, up from an initial recruitment goal of 30,000 individuals.
The U.S. Food and Drug Administration will have to approve the change before it goes into effect.
“The companies continue to expect that a conclusive readout on efficacy is likely by the end of October,” the press release said. The Pfizer and BioNTech study is likely to be among the first in the U.S. to report efficacy data from a Phase 3 trial.
Expanding the trial will likely make it easier for the company to demonstrate whether the vaccine is effective against SARS-CoV-2, the virus that causes Covid-19. The companies also said that the change will allow the study to include a more diverse population. The companies said the study will now include adolescents as young as 16, people with stable HIV, and those with hepatitis C or hepatitis B.
The companies said that the trial is expected to reach its initial target of 30,000 patients next week. Moderna, which started its trial on the same day as Pfizer, said on Sept. 4 that it is working to increase the diversity of trial participants in its study, “even if those efforts impact the speed of enrollment.”
The Pfizer/BioNTech study could finish sooner than Moderna’s, even though the two began on the same day, for other reasons, as well. Both vaccines require a second shot; Pfizer’s is given after three weeks, while Moderna’s is given after four. The Pfizer trial also starts to count cases of Covid-19 sooner after participants receive their shots than the Moderna study.
But the Pfizer/BioNTech vaccine could also prove to be one of the most difficult of the experimental vaccines to distribute, should they prove effective. The vaccine must be kept at a temperature of -70 degrees Celsius.
There has been political pressure to move a vaccine quickly, with President Trump saying that one could be available before election day. Last week, several drugmakers, including Pfizer, issued a pledge not to move a vaccine forward sooner than was justified by the results of their clinical trials.