Even though the Moderna (NASDAQ:MRNA) and Pfizer (NYSE:PFE)-BioNTech (NASDAQ:BNTX) vaccines have been authorized for emergency use by the U.S. Food & Drug Administration, we still have plenty of questions. How long will the immunity that they confer actually last? Will the vaccines protect against different mutations or strains of the virus? Dr. Bruce Gellin of the Sabin Vaccine Institute joined Olivia Zitkus and Corinne Cardina of the Fool.com Healthcare and Cannabis Bureau on a Dec. 18 episode of Fool Live to answer these questions and more.

Olivia Zitkus: What kind of data and information will you be watching for that gives us clues about the length of immunity, or on that same vein about viral mutations that could affect how the vaccine works over time?

Dr. Bruce Gellin: Those are two different questions. I think what we're going to be looking for is what's often heard is breakthrough; people who are vaccinated and then still get infected. Based on the efficacy numbers, we don't expect to see many of those cases. But there will be some because it's not a hundred percent effective, it's in the 90, 95, and that maybe different in the real world where things are not managed exactly as they are as meticulously in a clinical trial. But then the question is what happens as we follow-up people who've been vaccinated and have an infection? We'll have to look to see is there something about that virus that has escaped the immunity that's provided by the vaccine. That will give us some suggestion, if you will, about whether or not some of the mutations that have been seen are significant. Right now, though we've been seeing those mutations, it doesn't appear to change either the clinical picture of the disease or how the vaccine might work. We have to keep an eye on that. I think watching these breakthrough cases when they occur will give us a sense both in terms of resistance and the duration of protection.

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