The so-called interim analysis looked at the first 94 confirmed cases of Covid-19 among the over 43,000 volunteers who received either two doses of the vaccine or placebo. It found that less than 10 percent of infections were in participants who received the vaccine and over 90 percent of cases in people who received placebo.
The vaccine provides protection seven days after the second dose and 28 days after the initial dose, according to Pfizer. The ultimate goal of the trial is to reach a total of 164 confirmed cases of coronavirus infection to ensure statistical efficacy of the vaccine.
In a press release, the pharmaceutical giant announces that it plans to apply for permission to use the vaccine in emergencies from the US Food and Drug Administration, FDA, as soon as volunteers have been monitored for two months after receiving their second dose of vaccine. Pfizer expects to reach that marker by the third week of November.
The Phase 3 study of the Pfizer vaccine, conducted with German partner BioNTech, has registered 43,538 participants since July 27. As of Sunday, 38,955 of the volunteers have received a second dose of the vaccine.
"With today's news, we are a significant step closer to giving people around the world a much-needed breakthrough to end this global health crisis," said Pfizer CEO Albert Bourla in a statement.
"We look forward to sharing additional efficiency and safety data generated from thousands of participants in the coming weeks."
Pfizer says it has added a secondary endpoint to its study. It will evaluate whether the vaccines protect humans against severe Covid-19 disease and whether the vaccine can provide long-term protection against Covid-19 disease, even in patients who have been infected in the past.
The FDA has announced that it expects at least 50 percent efficacy from all coronavirus vaccines.