The Food and Drug Administration (FDA) has issued an emergency use authorization (EUA) for two coronavirus vaccines, but while short-term efficacy is clear, there are still plenty of unanswered questions. In this video from Motley Fool Live, recorded on Dec. 21, Corinne Cardina, bureau chief of healthcare and cannabis, and contributor Brian Orelli discuss the ethical issues over when to give the vaccine to the clinical trial participants who received a placebo. They also touch on some unknowns, including the length of immunity and why some people who received the vaccine still developed COVID-19.

Corrine Cardina: Moderna's (NASDAQ:MRNA) vaccine candidate, of course, was recommended for an emergency use authorization by the FDA advisory committee last week. The FDA issued that EUA, first doses are currently being rolled out. Brian, when we look at what came out of the advisory committee, was there anything discussed that is of particular interest for investors?

Brian Orelli: Yeah. The vaccine was obviously a home run, so the committee members were largely looking at post-authorization issues. For example, one of the biggest issues was the discussion about when to give the vaccine to the patients in the clinical trial that got a placebo. That essentially ends the trial. You can't compare somebody who got the vaccine to somebody else who got the vaccine. For those specific patients, it'll end the trial. Ideally, you want to keep the patients on the placebo as long as possible, but then there's the ethical issue of keeping people on placebo during the pandemic, which risks their lives.

Pfizer (NYSE:PFE) and BioNTech (NASDAQ:BNTX), have decided that they're going to give people a placebo when they would become eligible normally. Healthcare workers in the trial will get it earlier than you and I. Moderna is going to give it when people request it, they're using their development stocks that won't affect other people's place in line for getting the vaccine, and they said 25% of them are healthcare workers, so they'd probably get it early anyway.

There was a shockingly large amount of discussion during Moderna's advisory committee about Pfizer and BioNTech's vaccine. I guess there's some advantages to going second that you get to see what the committee asked them, but then it also means the first company's stealing their thunder a little bit because there was already some news out about Pfizer's vaccine.

Cardina: Absolutely. What are we still trying to figure out that the advisory committee did not yet have the answers to about this vaccine?

Orelli: Yeah, we still don't know the length of immunity and then there was a lot of discussion about protection after the first dose. It's pretty clear that the first dose was protecting patients that got the vaccine compared to those that got the placebo. But since almost everybody got the second dose as well, we don't really know whether that's a long term protection.

There were 11 cases in Moderna's trial of people who got the vaccine, who still got COVID-19, and so the question there is, did they not have a strong enough immune response? Which is fine that there's going to be a varied immune response and so it fine. But the bigger issue might be if there's mutations that are allowing infection in, but we need to sequence those and see whether that's the case.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.