MICHEL MARTIN, HOST:

Let's start today with that new information about coronavirus vaccines and booster shots. It's been coming in fast in recent weeks, and it can be confusing. So here's where we stand now. Booster shots of the Pfizer vaccine were approved for emergency use last month for individuals 65 and older and for others deemed to be at higher risk from COVID. Last week, a panel of experts advising the Food and Drug Administration made a similar recommendation for Moderna booster shots. And then the same panel advised that recipients of the Johnson & Johnson single-dose vaccine ages 18 and older become eligible for a second shot.

We asked Norman Baylor to help us sort through all this. Baylor is president and CEO of Biologics Consulting. He holds a doctorate in molecular biology, and he is the former director of the FDA's Office of Vaccines Research and Review. This is how he explains the FDA panel's recommendation of a second Johnson & Johnson dose for everyone who got the first shot.

NORMAN BAYLOR: You may recall that the Johnson vaccine had a lower efficacy than the Moderna vaccine and the Pfizer vaccine. So there is some concern about waning immunity. And if you're starting out with the lower efficacy, you may need a booster. When this vaccine was developed, part of their study did include a two-dose vaccine. But given the timing of that - of their vaccine and when their data came out, there was discussion about, well, we're getting a better efficacy than we thought we would get for any of these vaccines, so perhaps the one dose would be sufficient. But we're seeing now that the results with the two doses is actually much better with the Johnson vaccines.

MARTIN: So what about mixing and matching different vaccines? The question came up during the panel discussion at the FDA last week. And there have been studies showing that people who received the one-shot Johnson & Johnson vaccine matched with a Pfizer or Moderna booster showed a stronger antibody response. Is this safe? I mean, should people seek this method out?

BAYLOR: No, it's - I mean - even though we know people are doing that already. But we do not have sufficient data to make that determination at this time. The one thing that I think is really most challenging is you look at the science, and the preliminary science says that, yes, you do see that boost as far as antibodies. But can you make a public health decision at that point? Or do we need additional data, safety data as well as effectiveness data, to make that decision? I mean, individuals who received the Johnson & Johnson vaccine, perhaps it would be better to boost them with one of the mRNA vaccines. But it's still early to make a regulatory decision about whether you go that direction or not.

MARTIN: Because the vaccines work differently.

BAYLOR: The vaccines, they work somewhat differently. But there are caveats to the study. Again, I think it's important to understand that this study was designed for a public health decision. It was not powered to compare one group and the other.

MARTIN: That was Norman Baylor. He is the president and CEO of Biologics Consulting. He's the former director of the FDA's Office of Vaccines Research and Review. Norman Baylor, thank you so much for speaking with us today.

BAYLOR: My pleasure. Transcript provided by NPR, Copyright NPR.