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The drugmaker Pfizer said 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.

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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 million to 20 million people, company executives have said.

“This is a historical moment,” said Kathrin Jansen, a senior vice president and the head of vaccine research and development at Pfizer.

Independent scientists have cautioned against hyping early results before long-term safety and efficacy data have 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. Moderna has said it could have early results later this month.

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The news comes just days after Joe Biden clinched a victory over President Trump in the election. 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 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.

She said she learned of the results from the outside panel of experts shortly after 1 p.m. 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 on 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.

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Still, 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, director of the Yale Institute for Global Health.

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 FDA 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.

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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. 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.





Work on the vaccine began in Mainz, Germany, in late January, when Ugur Sahin, the chief executive and cofounder of BioNTech, read about the virus in the Lancet that filled him with dread. “I almost instantly knew that this would affect us,” Sahin said. That same day, the first European cases were detected, in France.

Sahin assembled a 40-person team to work on the vaccine. Many employees canceled vacations and Sahin authorized overtime pay. They called it Project Lightspeed.

BioNTech used a technology that had never been approved for use in people. It takes genetic material called messenger RNA and injects it into muscle cells, which treat it like instructions for building a protein — a protein found on the surface of the coronavirus. The proteins then stimulate the immune system and are believed to result in long-lasting protection against the virus. Other companies, including Moderna, are also using messenger RNA technology.

BioNTech quickly identified 20 vaccine candidates, and began testing them on rodents. But the company lacked the experience and resources to rapidly conduct a major clinical trial. So Sahin called Pfizer. The two companies had been working to develop a flu vaccine since 2018, and within a day of Sahin calling Jansen at Pfizer, the companies agreed to partner on a coronavirus vaccine.

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After early human trials, they determined that two vaccine candidates produced a robust immune response, including antibodies against the virus and powerful immune cells known as T cells. They chose the one with fewer side effects to start a trial with more than 30,000 volunteers in the United States, Argentina, Brazil, and Germany. In September, the company expanded the trial to 44,000 participants.

Even before it began, the Trump administration placed a bet that Pfizer and BioNTech would succeed, announcing its advance purchase deal July 22. At the time, it was the largest such commitment from the US government.











Wide distribution of Pfizer’s vaccine will be a logistical challenge. Because it is made with mRNA, the doses will need to be kept at ultracold temperatures. While Pfizer has developed a special cooler to transport the vaccine, equipped with GPS-enabled thermal sensors, it remains unclear where people will receive the shots, and what role the government will play in distribution. Adding to the challenge, people will need to return three weeks later for a second dose to complete the immunization.