Pfizer's Coronavirus Vaccine Is More Than 90% Effective, Early Data Says

The highly anticipated late-stage results are the first to be announced by a pharmaceutical company conducting a coronavirus vaccine trial.

The pharmaceutical company Pfizer announced extremely promising early results from its coronavirus vaccine trial on Monday morning as the world faces record high daily cases and deaths.

The company, which collaborated with the German pharmaceutical company BioNTech, is the first to report late-stage coronavirus vaccine trial results. The results, which did not include the actual data from their trial and have yet to be peer-reviewed, suggested that people who received the vaccine's two shots three weeks apart experienced 90% fewer cases of COVID-19 compared to those who received placebo injections. The company said no serious side effects have been observed.

The preliminary analysis is based on just 94 patients who developed COVID-19 in Pfizer's trial, which has enrolled over 43,000 patients. The efficacy numbers are expected to fluctuate as the trial continues to collect more data.

The extremely high level of protection is promising — and surprising — news after months of researchers cautioning that early coronavirus vaccines may not offer a high level of protection. The FDA only requires that a vaccine needs to be at least 50% effective in preventing illness.

"That’s pretty striking. We need to again see the data, but those are pretty striking numbers," said Paul Offit, a vaccine expert at Children’s Hospital of Philadelphia, who sits on the FDA vaccine advisory committee. "I’m pleasantly surprised," Offit said, adding that most experts were expecting to see the vaccine be 50 to 60% effective at preventing COVID-19 infections.

Eleven vaccines are currently in late-stage trials worldwide, with four frontrunners in the US sponsored by the federally funded Operation Warp Speed. In an interview with the New York Times, Pfizer's senior vice president, Kathrin Jansen, stated that the company did not take any money from Operation Warp Speed to pay for research and development of its vaccine.

For months, Pfizer had promised that its early results would be ready by October, fueling President Donald Trump's assertions that a vaccine would be ready by Election Day.

The early results instead came on the heels of a bitter election, as Joe Biden clinched the presidency.

Offit added that while the case numbers are still low, the high level of protection is very promising. The company was initially planning to conduct its first analysis when 32 participants developed COVID-19. But Pfizer said that, after discussions with the FDA, it decided to wait until 62 cases developed. While it was in discussion with the agency, 32 more people quickly got infected.

"There is a tyranny of small numbers here," Offit said. "If you stop at 32, how confident are you? When you’re at 94 and it's 90% effective, you gain greater confidence that that’s going to hold up over time."

The drug company said they are continuing to collect safety data required by the FDA, which says that half of the patients in the trial should be monitored for side effects for at least two months following their second shot, before asking the agency for emergency authorization to begin distributing its vaccine. The company expects to meet that milestone by the third week of November.

Once that data is collected, Pfizer projected that it is on track to produce 50 million vaccine doses in 2020 and up to 1.3 billion doses in 2021, to be distributed worldwide.

"These studies are being conducted much faster than we’ve ever seen before, because we’re in the middle of a pandemic," Offit said, pointing out that most vaccine trials take years to conduct.

"You can’t do that here," Offit said. "I’m sure everyone would feel better if this 90% efficacy wasn’t just for several months — that it was effective for a year or two years. But you can’t wait. You can’t do a three- to four-year study when this many people are dying. It’s not practical."

Offit said it would be helpful to receive more data in the future about whether the vaccine can prevent the severe cases of COVID-19 most at risk of causing hospitalizations and deaths, as well as information about whether it prevents asymptomatic infections. Since the vaccine is only months into its clinical trial, it is still not known how long it can prevent infection with the virus.

"It’s a much stronger result than I had anticipated and indicates that other vaccines have a good shot at success as well," Emory University biostatistician David Benkeser told BuzzFeed News by email. He noted that the trial should continue so that we can get more answers about how long immunity may last and whether the vaccine can prevent severe disease. "We’d obviously like to see the actual data, but the results released do look extremely promising."

The Pfizer vaccine belongs to a new class of messenger RNA (mRNA) gene injections, a type of vaccine never approved before for use in people. They carry the genes that instruct human cells to make viral proteins, triggering an immune response. A second frontrunner, produced by the pharmaceutical company Moderna, also uses mRNA for its coronavirus vaccine.

Pfizer last week said it would distribute the two-shot vaccine independently of the US government, from distribution centers in Michigan and Belgium. Its shots require storage at -94 degrees Fahrenheit, necessitating transport in dry ice and storage in specialized "ultra low temperature" refrigerators.

In public comments, FDA officials have indicated they would schedule a meeting of the vaccine advisory board of external experts who vote to recommend new vaccines once a pharmaceutical company requests emergency authorization to distribute its shots to the public. Those meetings usually come 15 days after the agency places a notice in the Federal Register.


This story has been updated with comment from Emory University's David Benkeser.

Topics in this article

Skip to footer