The drugmaker Pfizer said it will not apply for emergency use authorization for its Covid-19 vaccine candidate until at least the third week of November.
Pfizer CEO Dr. Albert Bourla made the announcement in an open letter published Friday. It means the EUA will not come before the presidential election.
"We may know whether or not our vaccine is effective by the end of October," Bourla wrote. But he went on to note that it will take weeks after that time to make sense of the data collected, determine how effective it is and confirm its safety.
Vaccine trials rely on a certain number of infections to occur. If more infections are reported among study participants who received the placebo than the actual vaccine, it's a good signal of efficacy.
But before any drugmaker can apply for emergency use authorization of a Covid-19 vaccine candidate, the Food and Drug Administration will require two months of safety information following the final dose of vaccine. Pfizer's vaccine requires two doses, about a month apart.
"Based on our current trial enrollment and dosing pace, we estimate we will reach this milestone in the third week of November," Bourla wrote.
"We are operating at the speed of science."
Two other drugmakers are testing their Covid-19 vaccines in phase 3 trials in the United States: Moderna and Johnson & Johnson.
AstraZeneca started its phase 3 study in September but halted it shortly afterward because of a safety issue in a study participant in the United Kingdom. That trial remains on hold in the U.S.