The drug maker Pfizer announced on Monday that an early analysis of its coronavirus vaccine trial suggested the vaccine was robustly effective in preventing covid-19, a promising development as the world has waited anxiously for any positive news about a pandemic that has killed more than 1.2 million people.
Pfizer, which developed the vaccine with the German drugmaker BioNTech, released only sparse details from its clinical trial, based on the first formal review of the data by an outside panel of experts.
The company said that the analysis found that the vaccine was more than 90 percent effective in preventing the disease among trial volunteers who had no evidence of prior coronavirus infection. If the results hold up, that level of protection would put it on par with highly effective childhood vaccines for diseases such as measles. No serious safety concerns have been observed, the company said.
Pfizer plans to ask the Food and Drug Administration for emergency authorization of the two-dose vaccine later this month, after it has collected the recommended two months of safety data. By the end of the year it will have manufactured enough doses to immunize 15 to 20 million people, company executives have said.
“This is a historical moment,” Kathrin Jansen, a senior vice president and the head of vaccine research and development at Pfizer, said in an interview. “This was a devastating situation, a pandemic, and we have embarked on a path and a goal that nobody ever has achieved — to come up with a vaccine within a year.”
Independent scientists have cautioned against hyping early results before long-term safety and efficacy data has been collected. And no one knows how long the vaccine’s protection might last. Still, the development makes Pfizer the first company to announce positive results from a late-stage vaccine trial, vaulting it to the front of a frenzied global race that began in January and has unfolded at record-breaking speed.
Eleven vaccines are in late-stage trials, including four in the United States. Pfizer’s progress could bode well for Moderna’s vaccine, which uses similar technology. A Moderna spokesman said that it expected interim findings from its study this month.
The news comes just days after Joseph R. Biden Jr. clinched a victory over President trump in the presidential election. Mr. trump had repeatedly hinted a vaccine would be ready before Election Day, Nov. 3. This fall, Pfizer’s chief executive, Dr. Albert Bourla, frequently claimed that the company could have a “readout” by October, something that did not come to pass.
Operation Warp Speed, the federal effort to rush a vaccine to market, has promised Pfizer $1.95 billion to deliver 100 million doses to the federal government, which will be given to Americans free of charge. But Dr. Jansen sought to distance the company from Operation Warp Speed and presidential politics, noting that the company — unlike the other vaccine front-runners — did not take any federal money to help pay for research and development.
“We were never part of the Warp Speed,” she said. “We have never taken any money from the U.S. government, or from anyone.”
She said she learned of the results from the outside panel of experts shortly after 1 p.m. on Sunday, and that the timing was not influenced by the election. “We have always said that science is driving how we conduct ourselves — no politics,” she said.
The data released by Pfizer Monday was delivered in a news release, not a peer-reviewed medical journal. It is not conclusive evidence that the vaccine is safe and effective, and the initial finding of more than 90 percent efficacy could change as the trial goes on.
“We need to see the actual data, and we’re going to need longer-term results,” said Jesse Goodman, a professor of medicine and infectious diseases at Georgetown University. Still, he said, “it’s a testament to hard work and science that we’re getting results that are so good and so fast.”
Other scientists were stunned by the data so far.
“This is really a spectacular number,” said Akiko Iwasaki, an immunologist at Yale University. “I wasn’t expecting it to be this high. I was preparing myself for something like 55 percent.”
If the final vaccine ends up with that level of efficacy, it “would be higher than your regular flu vaccine, and this vaccine could have a serious impact on bending the curve of this outbreak,” said Dr. Saad B. Omer, the director of the Yale Institute for Global Health.
Dr. Jansen said that because the trial is continuing, an independent board reviewing the data has not told her or other company executives other details, such as how many of the people developed mild VERSUS more severe forms of covid-19 — crucial information that the F.D.A. has said it will need to evaluate any coronavirus vaccine. The agency has also asked for other detailed data that could take weeks to review, including about how the company plans to manufacture millions of doses and ensure that the product is consistent and safe.
The trial is expected to continue until 164 people in the 44,000 person trial have developed covid-19, and will also evaluate how well it protects against developing severe forms of the disease, and how well the vaccine protects people who have already been infected with the coronavirus.
Half of the participants received two doses of the vaccine, and half received a placebo. The first analysis was based on 94 volunteers who developed covid-19. Dr. Jansen said the outside board did not say how many of those cases came from participants who had been vaccinated. But with a rate of more than 90 percent effectiveness, most had to have been in the placebo group.
Dr. Jansen said the global surge in coronavirus infections contributed to the speed with which participants in the trial got infected with the virus. “You can see for yourself, the rates are going up everywhere,” she said. “So we think based on our predictions, it shouldn’t take us very long” to get to 164 cases of covid-19.
Dr. Paul Offit, a professor at the University of Pennsylvania and a member of the F.D.A.’s vaccine advisory panel, said the news that Pfizer’s trial was progressing quickly was a good sign for other trials, too.
“If there’s any silver lining in the fact that our country is currently on fire with this virus, it’s that these trials can reach a conclusion much quicker than otherwise,” he said.