Johnson & Johnson announced yesterday that it had officially asked the Food and Drug Administration to authorize its COVID-19 vaccine, kicking off a process that will send its one-shot immunization through a gauntlet of analysts and experts.

If all goes as expected and the agency agrees that the benefits of the vaccine outweigh the risks, the United States could have a third shot available by the end of February. Experts hope that this vaccine — which only takes one dose and can be stored in the refrigerator — could accelerate the United States’ vaccination campaign.

Over the next few weeks, FDA officials will work at breakneck speeds to review the data submitted by Johnson & Johnson. Then, they’ll write up a report and submit it to the FDA’s independent vaccine advisory committee. That group will meet on February 26th, evaluate the data, and decide if they think the FDA should authorize the vaccine. (Their recommendation isn’t binding, but the agency usually agrees with it.) A day or so later, the FDA could release its decision.

Three weeks may seem like a long time to wait before the committee meets and the FDA makes its decision. And in the context of the pandemic, three weeks is a long time — thousands of people could die in that gap — but it’s actually remarkably fast given the enormity of the task at hand. The agency will use every second of that time to make sure there aren’t any safety concerns with the vaccine and that it can actually do what it claims to do. Skipping steps could erode already fragile trust in vaccination.

“FDA staff feel the responsibility to move as quickly as possible through the review process,” former FDA Commissioner Stephen Hahn said in December, just after Pfizer and BioNTech filed for authorization of their vaccine. “However, they know that they must carry out their mandate to protect the public health and to ensure that any authorized vaccine meets our rigorous standards for safety and effectiveness.”

Rather than just look at the reports done by the pharmaceutical company, the agency takes the raw data and runs its own analysis. Normally, that process takes around a year. For the COVID-19 vaccines, the agency dramatically shortened that timeline. It took 21 days from the time Pfizer and BioNTech filed for authorization for the vaccine to get the green light from the FDA. Agency experts worked in shifts, on nights and weekends, to crank through the data as thoroughly and quickly as possible, Hahn told The Wall Street Journal in December.

The data for this vaccine could be trickier to evaluate than the data for the Moderna and Pfizer / BioNTech vaccines, which were overwhelmingly effective against COVID-19. Johnson & Johnson’s vaccine was less effective overall but still kept anyone who took it alive and out of the hospital, even if they caught COVID-19. It was tested in the United States, Latin America, and South Africa. In South Africa, it encountered the coronavirus variant that appears to reduce vaccine efficacy. Understanding how well the vaccine works will take teasing apart the geographic differences in the trial.

The US has agreements for 100 million doses of the Johnson & Johnson vaccine, enough to protect 100 million people against the deadly effects of COVID-19. By the middle of the month, half a million people in the US will have died from the disease. The one-shot, logistically easy vaccine can’t come fast enough — but for now, it’s coming as fast as it can.