Why the U.K. Approved the Pfizer Covid Vaccine First

LONDON — The first rigorously tested coronavirus vaccine was given a green light for use on Wednesday in Britain. Doses of the vaccine, made by the American pharmaceutical giant Pfizer and a small German company, BioNTech, will be injected starting next week, the government said.

In leaping ahead of the United States to allow mass inoculations, Britain added to the pressure on American drug regulators, who were summoned to the White House on Tuesday by President Trump’s chief of staff to explain why they were not ready to do the same.

Why did Britain authorize a vaccine before the U.S.?

The two countries vet vaccines differently.

Rather than accepting the findings of vaccine makers, American regulators painstakingly reanalyze raw data from the trials to validate the results, poring over what regulators have described as thousands of pages of documents. Dr. Stephen Hahn, the commissioner of the Food and Drug Administration, called the United States an outlier when it comes to the rigor of its vaccine reviews, saying on Tuesday that the F.D.A. “is one of the few regulatory agencies in the world that actually looks at the raw data.”

Regulators in Britain and elsewhere in Europe lean more heavily on companies’ own analyses. Instead of sifting through raw trial data and crunching the numbers themselves, regulatory agencies often will study a drugmaker’s reports and, unless there are anomalies, ground their decisions in company-provided documents.

Still, scientists and industry experts said the British regulators maintained high standards, often acting as a bellwether for other countries’ rulings. The regulators themselves said on Wednesday that experts had “unprecedented access” to raw trial data; tested vaccines for quality, batch by batch; and read more than 1,000 pages of documentation.

American and British regulators also have different ways of soliciting outside views.

The F.D.A. consults an independent panel of experts before it decides. In the case of Pfizer’s vaccine, that panel will meet on Dec. 10. British regulators seek opinions from a specialist committee, too, but that group has the flexibility to review data and meet as it needs to, allowing it to move more quickly. In all, the committee met for more than 40 hours about the Pfizer vaccine, its chairman said on Wednesday.

Like American regulators, their British counterparts have been reviewing vaccine data as it arrived. And different teams worked in parallel, rather than waiting for other parts of the review to finish.

“If you’re climbing a mountain, you prepare and prepare,” Dr. June Raine, the chief executive of Britain’s Medicines and Healthcare Products Regulatory Agency, said on Wednesday. “We started that in June.”

When early results arrived on Nov. 10, she said, “We were at base camp.” And later, she said, “When we got the final analysis, we were ready for that last sprint.”

What about the rest of Europe?

Britain broke from the European Union’s regulatory orbit to approve a vaccine early, owing to emergency powers that the bloc gives countries in the case of a pandemic. Once Britain consummates its split from the European Union on Dec. 31, those powers to approve vaccines on its own will become permanent.

The countries that remain in the European Union are waiting for its regulator, the European Medicines Agency, to authorize a vaccine. Like the F.D.A., the European regulator has scheduled a meeting during which it will consult outside experts and offer an opinion on the Pfizer vaccine. That will happen on Dec. 29.

The agency’s job is complicated by its obligation to solicit the views of all 27 E.U. countries. That process has been accelerated during the pandemic, but it will still take several days for countries to weigh in after the Dec. 29 meeting, which is likely to delay vaccinations until early January.

When will the first doses arrive in Britain?

Pfizer plans to ship 800,000 doses to Britain in the coming days. Starting Tuesday night, those doses were being prepared for shipping at a factory in Puurs, Belgium, BioNTech said.

The doses will be packaged in boxes of several thousand doses each, with dry ice keeping them at the South Pole-like temperatures they require, before they are put on trucks or planes and taken to Britain. They will arrive in government distribution warehouses by the weekend, Pfizer said on Wednesday.

British hospitals have already begun emailing staff members to schedule vaccinations, with a London hospital system indicating that its first doses will be given at 7 a.m. on Monday. Britain placed advance orders for 40 million doses of the Pfizer vaccine but most of those are expected to be administered next year. Each patient needs two, a month apart.

Who will be vaccinated first in Britain?

A government advisory body released its list of vaccine priority groups on Wednesday. At the top of the list are nursing home residents and workers, followed by people older than 80 and health and social care workers.

In practice, though, government officials have indicated that frontline hospital workers may be quicker to receive vaccines because of the difficulties of storing and moving the Pfizer vaccine to nursing homes and other sites. It has to be stored at around minus 70 degrees Celsius (minus 94 Fahrenheit) until days before injection.

Pfizer has said that the vaccine can survive for five days in a normal refrigerator. But Britain’s National Health Service still has to consider issues like staffing at non-hospital sites and transport difficulties within the country in deciding how to administer the vaccine.

The British decision will not in itself bring vaccinations closer anywhere else. But Pfizer executives said on Wednesday that they had already heard from other countries that, in light of Britain’s go-ahead, were looking to accelerate their own approval processes.

American regulators, despite months of pressure from Mr. Trump, have maintained that they will follow their plan and review Pfizer’s vaccine to the F.D.A.’s standards.

The United States has pre-ordered 100 million doses of the Pfizer vaccine. Most of its supply will come from a separate factory in Kalamazoo, Mich. Still, many questions remain about how vaccine makers like Pfizer will fulfill the orders of wealthier nations that have procured supplies in advance.

Britain’s ruling offered little relief to poorer countries that could not afford to buy supplies in advance and may struggle to pay for both the vaccines and the exceptional demands of distributing them.