WASHINGTON — The Food and Drug Administration gave emergency use authorization Friday to the nation’s first coronavirus vaccine, launching what scientists hope will be a critical counteroffensive against a pathogen that has killed more than 290,000 Americans, shredded the nation’s social and political fabric and devastated the economy.

The historic authorization of the vaccine from Pfizer and BioNTech, just 336 days after the genetic blueprint of a novel coronavirus was shared online by Chinese scientists, sets in motion a highly choreographed and complex distribution process aimed at speeding vaccines throughout the United States to curb the pandemic.

The FDA action came after White House Chief of Staff Mark Meadows told FDA commissioner Stephen Hahn on Friday to be prepared to submit his resignation if the agency did not clear the vaccine by day’s end, according to people familiar with the situation who spoke on the condition of anonymity because they were not authorized to discuss what happened.

Meadows’ threat followed months of efforts by FDA scientists to try to ward off President Trump’s importuning on the vaccine and keep the review process apolitical and transparent in hopes of boosting public confidence in the shots. The FDA already had planned to clear the vaccine Saturday morning, and accelerating the authorization to Friday night was not expected to change the delivery timeline of the first shots.

The White House told Dr. Stephen Hahn, commissioner of the U.S. Food and Drug Administration, to approve the Pfizer vaccine on Friday or submit his resignation. Graeme Jennings/Pool via Associated Press

The nation set a record for COVID-19 deaths Thursday for the second day in a row, surpassing 3,300. The death tally for Friday was 2,950, only slightly lower, bringing the U.S. death toll to nearly 295,000.

Federal officials have said distribution of the first 2.9 million doses of the highly effective vaccine would begin within 24 hours of an authorization. Meanwhile, an advisory committee for the Centers for Disease Control and Prevention, which has recommended that health-care workers and nursing home residents be the first recipients, was expected to bless the vaccine on Saturday, paving the way for inoculations to begin early next week.

The vaccine achievement creates a paradigm for vaccine development, proving that fast and flexible technologies paired with a single-minded focus by pharmaceutical companies and government can accomplish in 11 months what typically takes years. And it marks a rare triumph for the Trump administration, which in many other areas – such as ensuring adequate testing supplies and providing consistent guidance on whether to wear masks – has failed to produce a coherent and sustained response to the crisis.

“It’s an all-capital-letters, followed by several exclamation points,” accomplishment, said Howard Markel, a medical historian at the University of Michigan who predicted that the scientists who are responsible will be lionized for ending the pandemic.

RAPID DEVELOPMENT

Daniel Carpenter, a political scientist at Harvard University, said it was unprecedented to go from the discovery of a disease to the development of a vaccine in 11 months. The shortest timeline previously was for the mumps vaccine, which took four years. Most vaccines are produced for ailments that have been around for a long time, after years of research often marked by failures and disappointments. In the case of AIDS, there still is no vaccine, nearly four decades after HIV was identified.

Pfizer and its Germany-based partner, BioNTech, harnessed a fast, flexible genetic technology that had been in development for decades but never deployed in an approved medical product. It was used to build a vaccine that surpassed all expectations by being 95 percent effective at preventing disease in a clinical trial with tens of thousands of participants. The vaccine has already been approved in Britain, Canada, Saudi Arabia and Bahrain.

Meanwhile, the FDA, working closely with the companies, conducted an accelerated review that compressed into three weeks the typical monthslong scrutiny of safety, effectiveness and data on manufacturing quality.

Operation Warp Speed, the administration’s effort to accelerate the development and distribution of coronavirus vaccines and treatments, has spent billions of dollars on a portfolio of vaccines, with Pfizer-BioNTech’s being the first to cross the finish line. Unlike the other companies, Pfizer and BioNTech did not take government money for research and development, but they did receive a $1.95 billion contract for 100 million doses, about 25 million of which will be delivered this year.

“To get there has required a host of innovations. … Any one of those would have been cause for considerable amazement,” said Francis Collins, director of the National Institutes of Health. “But when you put them together, it’s a path so revolutionary it would be hard to imagine somebody contemplating it five years ago.”

But while the vaccine enterprise has been impressive, its credibility has been repeatedly threatened by Trump, who for months pressured the FDA to authorize a vaccine before Election Day and, when that did not happen, bitterly accused the agency and Pfizer of deliberately orchestrating delays to harm his re-election prospects. On Friday, he continued his criticism on Twitter, calling the agency “a big, old, slow turtle,” adding, “Get the dam vaccines out NOW.”

The White House maneuvers seemed designed to ensure Trump gets credit just as the vaccine crosses the finish line. But experts said his behavior risked undermining public confidence – not because it would force a vaccine through prematurely but because it could create the appearance that politics, not science, drove the decision.

“There was no plausible way the FDA would not authorize this vaccine, ,,, but this makes it appear (their decision) is politically motivated,” said Dorit Reiss, a professor of law who writes about vaccine policy at the University of California Hastings College of the Law. “Making it appear there was political pressure will undermine trust.”

FDA CHIEF UNDER PRESSURE

Hahn, in a statement Friday, dismissed reports that his job was threatened. “This is an untrue representation of the phone call with the Chief of Staff,” he said. “The FDA was encouraged to continue working expeditiously on Pfizer-BioNTech’s EUA request. FDA is committed to issuing this authorization quickly, as we noted in our statement this morning.”

The White House said in an email that “we don’t comment on private conversations, but the Chief regularly requests updates on progress toward a vaccine.”

The political machinations are in sharp contrast to the impressive scientific achievement of producing a vaccine in record time. The Pfizer-BioNTech product, and the one right on its heels, from biotechnology company Moderna, use a snippet of genetic material encapsulated in a fat bubble to instruct cells to build the spiky proteins that dot the coronavirus. These shots will be the first time the genetic technology has been used in people outside clinical trials.

The government’s big bet on the promising method, which allowed for much faster vaccine development, was controversial but is paying off: Moderna’s shot is expected to be authorized shortly after a review by the FDA’s outside advisers scheduled for Thursday. The biotech companies behind the vaccines, Moderna and BioNTech, have never made a commercial product but ballooned into pharmaceutical heavyweights, with Moderna valued at $60 billion and BioNTech at $30 billion.

“I feel focused, and I feel also that this is a huge task,” said Ugur Sahin, chief executive of BioNTech.

BIG CHALLENGES AHEAD

While a potential lifesaver for those who receive it, the new coronavirus vaccine is not likely to have a dramatic impact on the immediate course of the pandemic. The supply of vaccines will initially fall far short of the 300 million doses some officials had hoped for last spring, when Operation Warp Speed was created.

In addition, formidable challenges lie ahead involving the massive scale-up of manufacturing and a complicated distribution plan overseen by cash-strapped states. On scientific questions, experts still do not know how long the vaccine’s protection lasts.

While the CDC’s Advisory Committee on Immunization Practices has recommended that health-care workers and nursing home residents be first in line for the vaccine, states ultimately will have the final say on which groups get priority. Much of the general population – including younger people who do not have underlying health conditions or jobs that put them at risk – are unlikely to be offered the vaccine before late spring or early summer. And if a significant proportion of Americans spurn the shot, efforts to banish the coronavirus or turn it into a low-level threat could be made much more difficult.

Still, the unquestionably good news on the Pfizer shot arrives as other vaccines also have moved forward: AstraZeneca and the University of Oxford published results in a peer-reviewed journal, China’s Sinopharm announced positive results, and Russia has reported promising data on a vaccine. But even multiple successful vaccines may not prove enough to reach all the world’s people.

“The entire world is seeing the light at the end of the tunnel, but for most of the world, they are still in a very, very long tunnel, and that’s the problem,” said Richard Hatchett, chief executive of the Coalition for Epidemic Preparedness Innovations, a nonprofit group that funds vaccine development. “The reason we’ve developed the vaccine is to end the pandemic, and you don’t end the pandemic until you … protect the most vulnerable people, who are globally distributed.”

The FDA’s action came the day after an agency advisory committee found that the benefits of the Pfizer vaccine exceeded the known risks and recommended that an emergency use authorization be granted for people 16 and older. The agency directed Pfizer to keep a close eye on possible allergic reactions after British health authorities reported two recipients had severe allergic responses after being vaccinated Tuesday.

FDA emergency authorizations are temporary approvals used to accelerate the availability of medical products during a public health emergency. They require less data than regular approvals and can be issued based on a lower standard. In the case of a vaccine, however, the FDA has said it would use rigorous criteria because millions of healthy people are expected to receive it.

THE FIRST SHOTS

The first 2.9 million shots are expected to be shipped to more than 600 sites – mostly large health-care systems – from Pfizer’s freezer farm in Kalamazoo, Mich., in special coolers packed with 50 pounds of dry ice. The vaccines must be kept at sub-Antarctic temperatures, by refreshing the coolers or by storing doses in an ultra-low-temperature freezer.

The government is holding back another 2.9 million doses for the second shot, to be administered 21 days later, and reserving 500,000 doses in case some are lost or spoiled. Officials say it will take time for nursing homes to coordinate with the pharmacy chains responsible for administering shots at those sites. CVS Health plans to administer the first shots of the Pfizer-BioNTech vaccine in nursing homes Dec. 21, according to spokesman T.J. Crawford.

Government officials project that Moderna and Pfizer will be able to deliver 40 million doses of vaccine this year, enough for 20 million people to receive the full regimen. The pace of vaccination is projected to increase in the first months of next year as manufacturing capacity increases and as other vaccines potentially come on line. Data on the effectiveness of a one-shot vaccine from Johnson & Johnson is expected in early January.

But long-term questions about the supply remain. The United States has secured only 300 million shots – enough for 150 million people – from Pfizer-BioNTech and Moderna and needs hundreds of millions of additional doses to cover the populace. The country has secured additional doses from other vaccine makers, but it is still uncertain whether those vaccines will be successful.

FDA scientists, in their review of the Pfizer data, confirmed the vaccine was safe and highly effective at preventing illness after two shots spaced three weeks apart. They identified a promising signal that the vaccine appeared to provide a level of protection even after a single shot, meaning that vaccinations could begin to have an impact sooner than many had expected.

VIRAL POLITICS

In its effort to clear the first coronavirus vaccine, the FDA has faced daunting technical and political challenges.

For months, the agency has tried to balance pressures to expedite the vaccine with the need to keep standards high, to reassure the public that a vaccine produced in record time would be safe and effective.

Adding to the sensitivity was the agency’s effort to bolster its own credibility. Its image was tarnished when earlier in the year it authorized hydroxychloroquine, a malaria medicine that Trump repeatedly touted as a COVID-19 treatment, then revoked that authorization when subsequent data showed it could be harmful.

In August, Hahn overstated the benefits of another treatment, convalescent plasma, during a briefing with Trump. Stung by criticism from the scientific community, Hahn apologized and began speaking out about the importance of agency career scientists’ making independent decisions.

Peter Marks, director of the agency’s Center for Biologics Evaluation and Research, which oversees vaccines, said during a recent American Medical Association webinar that the FDA helped expedite the clinical trial process by eliminating “dead spaces” that typically occur between phases of investigation by vaccine makers.

To ensure that companies understood the FDA’s expectations, the agency took the unusual step of issuing guidelines in June that specified any vaccine should be at least 50 percent effective compared with a placebo, or saltwater shot. A few months later, after it became clear the agency would employ an emergency use authorization to clear the vaccine, the FDA spelled out detailed standards and called for the manufacturers to produce two months of safety data on half of the trial participants.

That safety requirement meant any vaccine would be delayed until after Election Day, infuriating Trump, who tweeted angrily about the FDA and Pfizer. White House ire intensified when Britain authorized the vaccine first, on Dec. 2.

On the AMA webinar, Marks acknowledged that the agency had paid a price for its careful scrutiny. “Unfortunately, there is a cost to being this careful. Another regulatory agency made the vaccine available before we did,” he said. “That’s because we are really taking care to make sure when people get this vaccine, we will have really vetted it for safety.”

Harvard’s Carpenter said being careful will pay off in the long run with greater acceptance of the vaccine, boosting public health. “You need to think about the confidence effects,” he said.