A COVID-19 vaccine candidate was 90 percent effective at protecting people from the coronavirus, manufacturers Pfizer and BioNTech said on Monday. The Food and Drug Administration (FDA) previously said it would require any vaccine to be at least 50 percent effective in order to be approved.

“If that headline really number really holds up, that is huge. That is much better than I was expecting and it will make a huge difference,” Ashish Jha, the dean of the School of Public Health at Brown University, told STAT News.

The extraordinary claim is based on early data from a massive trial that’s enrolled 43,538 people so far. Pfizer and BioNTech have only released some of the data publicly in their announcement this morning, and it has not been reviewed by independent scientists. The companies are still gathering information from the trial and cautioned in the announcement that the “final vaccine efficacy percentage may vary.”

Pfizer and BioNTech’s vaccine is built using a still-unproven gene-based technology. The strategy works by introducing a tiny snippet of the coronavirus’s genetic material to the body. Then, cells use instructions encoded by the genetic snippet to create that piece of virus, and the immune system learns to fight against it. Moderna’s vaccine candidate uses the same strategy.

Gene-based vaccines have to be stored at ultracold temperatures, which make them more difficult to transport. The Pfizer / BioNTech vaccine also takes two doses, which have to be given three weeks apart — which makes it more logistically complicated to distribute than vaccines that only need one shot. The companies claim that “protection is achieved” seven days after a patient gets their second dose. It’s not clear how much protection would be offered by just one of the two doses.

Before the vaccine can be used, it needs to be authorized by regulatory bodies, including the FDA, which will look at both how safe and effective the vaccine is. No serious safety concerns for this vaccine have been reported. But the information released today doesn’t include information on how many people developed more severe forms of the disease and how many had milder cases — information the FDA will consider in their evaluation.

The companies say they should have enough safety data from their studies to file for Emergency Use Authorization from the FDA by the third week of November.

Pfizer and BioNTech have an agreement with the US Department of Health and Human Services to provide up to 600 million doses of their vaccine for $1.95 billion. The companies said that they could manufacture 50 million doses of the vaccine this year and 1.3 billion doses in 2021.

Even if this vaccine is authorized by the FDA, it won’t be available to everyone immediately. It will likely be distributed to health care workers first and then to other groups at high risk for severe cases of COVID-19, like essential workers and people with preexisting conditions. A big challenge still ahead is the logistics of getting shots in the arms of people who need them most.

A number of other pharmaceutical companies have vaccine candidates in phase three clinical trials, and initial results from some of those trials could be released soon, as well. More than one could prove to be effective, and the FDA could authorize more than one. The Coalition for Epidemic Preparedness Innovations said last month that it would run studies comparing the options, in the hopes of identifying which could work best.

Developing a vaccine is an important step in efforts to fight the spread of the virus, but it can’t bring the pandemic to an immediate end. It’ll take months — at least — to get people vaccinated. Meanwhile, the virus continues to rage around the globe, and the United States is seeing record-shattering spikes, with more than 100,000 cases reported daily. To slow the rampant spread of the disease, people will still need to wear masks, wash their hands, and keep their distance from each other.

“It is not going to eliminate the need to be prudent and careful with our public health measures,” Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said last month.