Earlier this month, coronavirus vaccines from Moderna (NASDAQ:MRNA) and the team of Pfizer (NYSE:PFE) and BioNTech (NASDAQ:BNTX) received Emergency Use Authorization from the U.S. Food and Drug Administration. Does this mean that it will be more challenging for companies to enroll participants in clinical trials for vaccines still under development? Dr. Bruce Gellin of the Sabin Vaccine Institute joined Olivia Zitkus and Corinne Cardina of Fool.com's Healthcare and Cannabis Bureau on a Dec. 18 episode of Fool Live to talk about what's ahead for the next COVID-19 vaccines. 

Olivia Zitkus: For those vaccines that are still in those earlier stages of development that might not be getting the attention that Pfizer and Moderna are getting right now, there are still lots of them out there, how easy or difficult do you think it will be to enroll people in those clinical trials now that another vaccine has received emergency use authorization and vaccinations have started?

Dr. Bruce Gellin: That's really an important question. That was a large part of the discussion of the FDA advisory committee yesterday, and these are marathon sessions. Nine hours of Zoom is a lot for anybody, but they spend a lot of time asking committee for their advice on how to go forward, just where we are right now. The short story is that right now people were randomized in the current vaccine trials to either receive the vaccine or placebo. Well, now, if you receive the placebo, which you shouldn't know, but maybe you do because of your reactions, but you receive a placebo, you think, "Well, wait a minute, I'm walking around. Why don't I get protected?" There is this question about the ethical obligation some of the companies feel to provide the protection for those people versus the fact that you're going to lose a lot of information if you un-blind the studies and have people now all be vaccinated, so it was a large part of that discussion. I think that in the near-term, this is not going to be such a problem because with relatively small supplies, it shouldn't be so difficult to enroll people in a study if they're not going to get vaccine for very long. I know we'll probably talk about that, that New York Times article to think about where you are in line. But it's going to be a while, so maybe there's going to be an incentive for people to enroll in the study if they think they can get a vaccine as part of that study. Over time, that's going to be more complicated. I think the answer to that, which is easy to say but hard to do is, is the science part, that if we can come up with what are called these correlates of protection. What can you measure in a laboratory that says, if you have this level of antibody or if you have this level of T-cell or level of something, you are protected. Right now, we don't have that. We know relatively how that works, but that's why the clinical trials are done. If we could figure out these correlates of protection, then we wouldn't have to have these massive trials, and we will know in a smaller subset of people if some other experimental vaccine will provide this kind of protection.

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