WASHINGTON: Pfizer's COVID-19 vaccine faces one final hurdle as it races to become the first shot greenlighted in the US: a panel of experts who will scrutinize the company’s data for any red flags.

Thursday’s meeting of the Food and Drug Administration’s vaccine advisory panel is likely the last step before a U.S. decision to begin shipping millions of doses of the shot, which has shown strong protection against the coronavirus.

The FDA panel functions like a science court that will pick apart the data and debate — in public and live-streamed — whether the shot is safe and effective enough to be cleared for emergency use. The non-government experts specialize in vaccine development, infectious diseases and medical statistics. The FDA is expected to follow the committee’s advice, although it is not required to do so.

The FDA’s decision comes as the coronavirus continues surging across much of the world, claiming more than 1.5 million lives, including more than 289,000 in the U.S.

Hanging over the meeting is a warning from U.K. officials that people with a history of serious allergic reactions shouldn’t get the vaccine. Government officials there are investigating two reports of reactions that occurred when the country began mass vaccinations.

Still, a positive recommendation and speedy U.S. approval seem nearly certain after FDA scientists issued an overwhelmingly positive initial review of the vaccine earlier this week.

FDA said results from Pfizer’s large, ongoing study showed the shot, which was co-developed with Germany’s BioNTech, was more than 90% effective across people of different ages, races and underlying health conditions, including diabetes and obesity. No major safety issues were uncovered and common vaccine-related side effects like fever, fatigue and injection site pain were tolerable.

“The data presented in the briefing report were consistent with what we heard before and are really exciting,” said Dr. William Moss, head of Johns Hopkins University’s International Vaccine Access Center. “Nothing that I see would delay an emergency use authorization.”

The meeting also gives regulators an opportunity to try to boost public confidence in the breakneck development process that has produced the Pfizer-BioNTech vaccine and a string of other upcoming shots in less than a year. The FDA has also faced weeks of verbal abuse from President Donald Trump for not rushing out a vaccine before Election Day.

“There have been a lot of questions about why it takes us so long or ‘are we being rigorous enough?’” said FDA Commissioner Stephen Hahn in an interview. “I’m hoping that people will see with our transparency that we have taken a very rigorous stance on this.”

Hahn said the agency has already teed up the process to authorize the vaccine by filling out all the legal paperwork in advance, regardless of the ultimate decision.

On Thursday's agenda:

RARE ADVERSE REACTIONS

The FDA uncovered no major safety issues in its review of Pfizer’s 44,000-person study, including no allergic reactions of the type reported in the U.K. But such studies can’t detect rare problems that might only affect a tiny slice of the general population.

FDA reviewers noted four cases of Bell’s palsy that all occurred among people getting the vaccine. They concluded the cases were likely unrelated to the vaccine because they occurred at rates that would be expected without any medical intervention. But the agency did say cases of the nerve disorder should be tracked, given that other vaccines can cause the problem.

“I think we have to be upfront, without scaring people, that we don’t know yet about any potential, rare, long-term adverse events,” Moss said.

EFFICACY QUESTIONS

The FDA found the vaccine highly effective across various demographic groups.

But it's unclear how well the vaccine works in people with HIV and other immune-system disorders.

The study excluded pregnant women, but experts will tease apart the data for any hints in case women get vaccinated before realizing they're pregnant.

A study of children as young as 12 is underway.

IMPACT OF EMERGENCY AUTHORIZATION

Answering some of these questions will require keeping Pfizer’s study going for many more months.

When the FDA panel met in October, experts warned against allowing trial participants who received placebos to switch and get the real vaccine immediately after it receives the FDA's emergency OK. Doing that could make it impossible to get answers to long-term questions, including how long the protection lasts.

Pfizer and BioNTech say they want to allow such participants to get the vaccine either upon request or, at the latest, after six months of follow-up.

The FDA still hasn’t made clear if it will accept that approach.

“FDA is adamant that they want these trials completed,” said Norman Baylor, former director of FDA’s vaccine office, adding that its expert panel members "know that too.”