Should people who get a COVID booster get a different vaccine from their original shot? The results of a highly anticipated study suggest that in some cases the answer may be yes.

Transcript

SARAH MCCAMMON, HOST:

Since public health experts first started talking about COVID-19 vaccine boosters, people have wondered, is it best for vaccinated folks to get the same vaccine for their booster as they did for their initial shots? Or would it be better to mix things up and get a different vaccine as a booster? A highly anticipated study has produced some provocative answers. And joining us now with all the details is NPR health correspondent Rob Stein. Hi, Rob.

ROB STEIN, BYLINE: Hey there, Sarah.

MCCAMMON: OK, so you've got me wondering, what did they find?

STEIN: The bottom line is if you got either the Pfizer or the Moderna vaccine, it looks like a Pfizer or a Moderna shot would work well as your booster. Moderna seems to work the best, but not all that much better than Pfizer. So if Pfizer or Moderna was your first vaccine, it doesn't look like it matters very much as long as their booster is another one of these so-called mRNA vaccines.

But if you got the J&J vaccine, it really looks like you'd get the best response if you don't get another J&J. The best is either getting Moderna or Pfizer next. The levels of so-called neutralizing antibodies in people who got one of those shot up 10 to 20 times higher than if they just had another J&J shot. And that's probably a big enough difference to provide stronger protection. How much stronger isn't known. This study wasn't large enough to see how things like, you know, how sick people would get or how much - you know, if they would get sick at all. But based on other research, that's probably enough to make a significant difference.

MCCAMMON: So it sounds like better results with Moderna or Pfizer. How did they arrive at this conclusion, Rob?

STEIN: Yeah, it comes from a big study sponsored by the National Institutes of Health that was designed to see whether people should get the same vaccine as a booster or instead should, you know, like you said, mix it up this time. The researchers divided 458 volunteers who initially got either Moderna, Pfizer or Johnson & Johnson into different groups. They either got the same vaccine as their booster or got one of the other two instead four to six months later. The researchers then measured their antibodies two and four weeks after the boosters, and the results were these really interesting findings.

MCCAMMON: And so for people looking to get a booster, what does all this mean?

STEIN: Yeah, you know, the first thing I should mention is that there are some caveats to this study that make it a little hard to know how to interpret. First of all, the researchers tested full doses of all the vaccines, not the half dose that Moderna is seeking authorization for its booster. Also, they measured antibody levels two and four weeks after their booster. So there's a chance antibody levels from a J&J booster could continue to rise with more time. Or, you know, the antibodies from the others could fall faster. And they're assuming that antibody levels translate into more protection. That's probably true, but other factors may also play a role, such as how other parts of the immune system respond.

All that said, this does suggest that people who got the J&J would benefit the most from getting one of the mRNA vaccines next time around, perhaps because using an entirely different kind of vaccine just does a better job of, you know, amping up the immune system.

MCCAMMON: OK, you're talking about mixing things up, Rob, but that's not what the company is asking the FDA to do, is it?

STEIN: Yeah, that's right. J&J is seeking authorization for a second one of its own shots. And the company is saying the protection from its vaccine looks like it is more long-lasting. So, you know, it'll be interesting to see what advisers to the Food and Drug Administration who are meeting starting tomorrow to make recommendations to the agency do with this information. The FDA seems to be questioning how strong the company's evidence is for its booster, but perhaps the FDA could OK a J&J booster but say, you know, using one of the others as a booster could be a better option whenever they're available.

MCCAMMON: NPR health correspondent Rob Stein, thanks.

STEIN: You bet. Transcript provided by NPR, Copyright NPR.

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