LIVE BLOG: An FDA expert panel is meeting to discuss how good Pfizer's coronavirus vaccine really is. Here's what to expect in a landmark day for a COVID-19 shot.

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've 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?