An FDA expert panel is discussing Pfizer’s COVID-19 shot as the pandemic rages. Here’s the 1 key question they’re considering.

• A group of independent experts is meeting Thursday to discuss what is likely to be the first coronavirus vaccine available in the US.
• The US Food and Drug Administration convened the advisory committee to vet Pfizer’s COVID-19 shot.
• The panel will ultimately vote “yes” or “no” to whether the FDA should green-light the shot.
• Even if the advisory group votes in favour of OK’ing the vaccine, the FDA still has the ultimate authority to make the regulatory decision on its own. The agency typically follows the advice of these expert panels but it isn’t required to do so.
• Healthcare and science reporters Andrew Dunn and Hilary Brueck are covering the meeting. Follow along this live blog for their updates on what’s happening.
• For more stories like this, sign up here for Business Insider’s daily healthcare newsletter.

9:45 AM: The committee is an impressive mix of more than 20 virologists, doctors, and leading public health experts. There’s one lawyer and one competing pharmaceutical maker in attendance too.

Some of the more prominent committee members from the world of medicine include:

• Dr. Eric Rubin, an infectious-disease specialist and editor-in-chief of The New England Journal of Medicine.
• Dr. Paul Offit, a top vaccine expert at the University of Pennsylvania who co-invented the rotavirus vaccine.
• Dr. Cody Meissner, chief of the pediatrics infectious disease division at Tufts University School of Medicine.
• Dr. Stanley Perlman, a virology professor from the University of Iowa who has been studying coronaviruses for nearly four decades.

Dr. Paula Annunziato, who works in vaccine research at Merck is the non-voting industry representative, and Sheldon Toubman, a lawyer from New Haven, is attending as a consumer representative. He often works as a legal aid lawyer for low-income families.

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9:04 AM: As meeting gets underway, FDA reveals the question of the day.

The expert panel is now underway, virtually, starting with opening remarks and introductions led by the committee’s chair, Arnold Monto, a professor of epidemiology and global public health at the University of Michigan.

These meetings typically take quite a while – finishing by 5:15 p.m. is more a goal than a hard stopping point. The most interesting discussion usually comes close to the end of the day, when the committee is allowed to have a free-flowing dialogue ahead of the big vote. On today’s agenda, that should start around 3:10 p.m.

The FDA committee will only vote on one yes-or-no question at the end of the day:

“Based on the totality of scientific evidence available, do the benefits of the Pfizer-BioNTech COVID-19 Vaccine outweigh its risks for use in individuals 16 years of age and older?”

New documents released just now show the FDA wants the panel to also weigh in on a couple of hot topics. First, what should researchers do with trial volunteers who received a placebo shot? There’s a difficult tradeoff between the benefits of following those people for long-term data at the cost of withholding an effective vaccine and exposing them to the pandemic.

Secondly, the agency is asking the group to discuss if they see any gaps in the plans to evaluate the safety and effectiveness of the shot going forward.

9:01 AM: FDA boss Stephen Hahn says “we intend to act quickly” after today’s meeting.

FDA Commissioner Stephen Hahn.

The head of the FDA told NBC’s Savannah Guthrie he will listen to the advisory committee’s discussion today, but ultimately, it’s up to him and the FDA’s in-house scientists to decide whether to approve or reject the Pfizer vaccine for emergency use in the US.

And, he hinted that the agency may already be leaning towards a favourable decision for Pfizer’s shot, saying “our initial assessment is that this is a vaccine that does meet our criteria.”

“We have the advisory committee to get outside opinions about this,” commissioner Hahn said Thursday morning on TODAY.

“We think it’s very important for transparency. We’re the only regulatory agency in the world that has a public vetting of the data. But we’ll make that decision. Our scientific experts will make that decision.”

Hahn also suggested that official decision could come as soon as this evening, shortly after the committee’s vote:

“We’ll have to see what the scientific and medical discussion is today. But our plan is to take their recommendations into account for our decision making and make a decision shortly thereafter. Again, it really depends upon the complexity of the issues discussed, but we intend to act quickly.”

8:00 AM: 7 unanswered questions we expect answers for today.

The advisory committee meeting is set to begin one hour from now, at 9 a.m. ET, with a very full agenda slated to last until 5:15 p.m.

Unlike many FDA advisory committee meetings, the pros and cons of the vaccine aren’t likely to stir much debate, given the scale of the coronavirus outbreak across the US right now. It’s widely expected that the committee will recommend the vaccine should receive emergency use authorization – teeing up the FDA to officially OK the vaccine to go into arms across America in the coming days.

We’ve already seen lots of data about this vaccine, both in what Pfizer initially described in November about the shots’ efficacy, and in far more detail through independently-vetted briefing documents released Tuesday by the FDA. Those documents showed FDA scientists making the case that Pfizer’s vaccine had no major safety concerns, and was overwhelmingly protective – 95% effective at preventing symptomatic COVID-19.

Even so, the devil is often in the details. Some of the most interesting debates we expect today will be on nuanced topics, with this group of virologists, vaccine experts, and biostatisticians digging deep to get the full picture about what we know – and don’t know – about this shot.

Here are seven of the most burning questions we are most eagerly looking forward to (hopefully) hearing some answers to today:

1. How much protection do people get after their first shot? Data released Tuesday suggested one Pfizer shot was about 50% effective at preventing COVID-19 in the 21-day period until people got their second (booster) shot. If that partial protection is legit, that would be a valuable benefit to know when immunizing people. Although experts have stressed it will still be essential to get the second dose for the more robust, 95% protection.
2. How durable is the protection? Given that Pfizer’s earliest coronavirus vaccine trials only started a few months ago, we probably won’t know how long Pfizer’s vaccine protection typically lasts, but the committee can unearth any new information they have discovered about waning immunity. Is the trial showing any signs that participants who’ve had the vaccine for several months now are losing their protection? Or is it still too early to tell?
3. Does the vaccine also prevent transmission to unvaccinated people? The Pfizer vaccine trial was designed to measure if the shots prevent people from getting symptomatic disease, the kind of coronavirus that might prompt a fever, cough, or more serious issues. The results are an unambiguous success on that front. But that doesn’t necessarily mean the vaccine can stop people from being infected. If vaccinated people can still be asymptomatic carriers, unknowingly spreading the virus to others who have not yet been vaccinated, that would have big public-health consequences. Is there any data to suggest one way or the other whether the shot provides so-called ‘sterilizing immunity’?
4. What happens to the placebo group now that we know the shot works? Half of the roughly 40,000 volunteers in Pfizer’s trial got a placebo shot (aka no treatment) and they still don’t know they’re walking around vaccine-free. Keeping the study blinded allows researchers to continue to gather valuable information – particularly in figuring out the durability of the vaccine’s protection. But it poses an ethical conundrum as well. When should the placebo group be offered the real vaccine, particularly if it’s known to be very safe and effective? The committee is likely to have thoughts on what should happen next.
5. Is there enough data on really old people to classify the shot as fully safe for them? We’re not talking about the 55-plus seniors group, but people in their 80s and 90s. With nursing homes being a top immunization priority, this is a relevant population to make sure will be safe to vaccinate. Data released Tuesday showed 860 people in Pfizer’s trial (out of more than 21,000 participants worldwide) were over the age of 75, with the oldest person being 89 years old. Is that a rigorous enough experiment to satisfy the committee and OK this shot to be rolled out to nursing homes across the nation?
6. What can we learn from the non-responders?Some of the most valuable insights may be gleaned from people who got Pfizer’s vaccine and still got sick. Fortunately, there weren’t a lot of them. Just one volunteer on the active arm registered a severe case of COVID-19 (compared to nine severe cases who were given the placebo) and there were eight cases of COVID-19 overall who got Pfizer’s shot (compared to 162 in the placebo group). Can that handful of cases tell us something we don’t know about who may or may not respond poorly to this vaccine?
7. What about allergic reactions? UK health regulators have warned that people with a history of severe allergic reactions shouldn’t get Pfizer’s shot, after two adverse events were observed in the British rollout. Is there a suitable explanation from Pfizer for why that may be a case, particularly given this vaccine was developed using messenger RNA, a new technology platform? And will this expert panel make a similar recommendation in restricting who should get the shot?