A decision on whether Pfizer Inc. and BioNTech SE can market their COVID-19 vaccine for emergency use in the U.S. will come in "days to a week" after a U.S. Food and Drug Administration advisory committee meets Dec. 10, a top regulator said.

"It will all depend a little bit about how things come out," Peter Marks, director of the FDA's Center for Biologics Evaluation and Research, said during a Dec. 9 virtual forum hosted by the Alliance for a Stronger FDA.

But Marks said he was willing to "get off the dime" and say "it'll be from days to a week" following the recommendations of the FDA's Vaccines and Related Biological Products Advisory Committee.

Members of the White House's Operation Warp Speed project, including its senior scientific adviser, Moncef Slaoui, had predicted earlier that the FDA would act within hours of the advisory committee rendering its verdict on the vaccine and shipments of the product could go out to states Dec. 11. But Marks' timeline puts that later.

The FDA panel will vote at the end of the all-day Dec. 10 meeting on whether the totality of the scientific evidence available is sufficient to grant emergency use authorization, or EUA, to the Pfizer-BioNTech two-dose vaccine for preventing COVID-19 in people age 16 or older and if the potential benefits outweigh the risks.

The FDA is not bound by its outside advisers' recommendations, "but we take very seriously what the experts on this committee will tell us," Commissioner Stephen Hahn said during the Dec. 9 forum.

Hahn acknowledged the significance of the FDA meeting and the agency's decision to a nation waiting for a vaccine to end the pandemic, which has taken the lives of nearly 300,000 Americans.

"Who would have thought a year ago that EUA would be part of the national lexicon and that people would even be talking about it," Hahn said.

An FDA analysis of Pfizer's and BioNTech's phase 3 data from a 44,000-person study showed the vaccine, known as BNT162b2, was highly effective in preventing laboratory-confirmed COVID-19. The vaccine also demonstrated a favorable safety profile with no major concerns that would preclude the agency from granting an EUA, regulators said in briefing documents posted Dec. 8 ahead of the advisory committee meeting.

Side effects

However, there were a number of side effects reported in the trial, such as injection site reactions, fatigue, headache, muscle pain, chills, joint pain and fever.

Lymphadenopathy, or swollen or enlarged lymph nodes, and Bell's palsy, a condition that causes temporary weakness or paralysis of the muscles in the face, were also reported and events the FDA said should be monitored for when the vaccine is used in the broader population.

Health officials in the U.K. on Dec. 9 warned that people with a significant history of allergic reactions should not be given the Pfizer-BioNTech vaccine after two people in that country experienced anaphylaxis after getting the first doses of the two-dose shot.

Both people in the U.K., who are healthcare workers, had a history of allergic reactions and were carrying adrenaline auto-injectors to counter the reactions.

The U.K. was the first country to authorize the Pfizer-BioNTech shot, with Bahrain and Canada following days later.

The FDA's Marks said his agency was working with U.K. health officials on investigating the two allergic reactions.

He noted that having a history of allergic reactions was a contraindication for enrollment in trials of the Pfizer-BioNTech vaccine.

"We'll continue to investigate and make sure we understand what's going on here," Marks said. "Obviously, we'll continue to keep the public informed."

But he acknowledged the task ahead of getting people to understand there will be some side effects with the COVID-19 vaccines "and that's normal."

The Pfizer-BioNTech vaccine is based on a messenger RNA platform, as is another product from Moderna Inc. and its partner the U.S. National Institute of Allergy and Infectious Diseases, or NIAID.

Messenger RNA plays a fundamental role in human biology, transferring the instructions stored in DNA to make the proteins required in every living cell.

If authorized by the FDA, the Pfizer-BioNTech and Moderna-NIAID products will be the first mRNA vaccines on the U.S. market.

But Marks said the U.K. health officials had overreacted to the two allergic reaction reports and were too quick in issuing a broad warning.

"I understand the need, that feeling that regulators might have that we've got to get everything out there really fast," he said. "But we also have a responsibility not to yell 'fire' when we don't know. It's like yelling 'fire' in an auditorium here when you smell a little burnt popcorn. We need to go to the popcorn maker and make sure it's not on fire."

One-dose confusion

Marks also said he was concerned about some misinterpretations of a statement in the FDA's Dec. 8 briefing documents that said vaccine efficacy in the trial after the first dose was 82% in the all-available efficacy population and that based on the number of cases accumulated after dose 1 and before dose 2, "there does seem to be some protection against COVID-19 disease following one dose."

Some people had misinterpreted that statement to mean the Pfizer-BioNTech vaccine was effective after a single dose, he said.

"But actually what they meant was those people who received the first dose, if you take that time interval and include the time between that and the second dose and everything going forward, it's [82%] effective if you got the second dose," Marks said. "If you don't get the second dose, we don't really know the effectiveness and we don't know how long the protection lasts."

Marks emphasized people need to get the second dose to experience the full protection of the Pfizer-BioNTech vaccine, which demonstrated efficacy of 95% in preventing symptomatic COVID-19.