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Scientists May Have Found A Marker Of How Effective COVID-19 Vaccines Are

ARI SHAPIRO, HOST:

Scientists have just published a study that could be pivotal to the future of COVID-19 vaccines. They found markers in people's blood that indicate whether a future vaccine will work or not. This could speed up the approval process for vaccines intended to protect against new variants. Joining us to talk about the study is NPR science correspondent Joe Palca. Hi, Joe.

JOE PALCA, BYLINE: Hello, Ari.

SHAPIRO: We have Joe Palca with us. OK, there's a long delay on the line, but we will deal with it. What are these markers in the blood, and how did scientists find them?

PALCA: Well, the markers are different antibodies. And they - the researchers looked at people who participated in the large trial of the Moderna vaccine, the one involving 30,000 volunteers that was used to get the vaccine authorized. In particular, they studied people who had been vaccinated but subsequently got infected and then got sick with COVID. And the idea was to see if they could find any signal in their blood that would predict why these people got sick and others did not.

Peter Gilbert from the Fred Hutchinson Cancer Research Center was one of the directors of the study. Gilbert says he and his colleagues compared the levels of antibodies in people who were vaccinated and stayed healthy with the levels of antibodies in people who were vaccinated but got sick.

PETER GILBERT: They were always lower in the vaccinated people who became a COVID case compared to people that remained free of COVID.

PALCA: And this is what you'd expect. The people who were vaccinated and still got COVID did not have the same robust immune response to the vaccine as others did.

SHAPIRO: Why is knowing that important for approving vaccines?

PALCA: Well, scientists have been looking for something they call correlates of immunity, something in the blood that would predict whether a vaccine would work. And Gilbert says finding these markers in the blood should be extremely useful.

GILBERT: Because that could be used as the basis for authorization and approval of vaccine candidates without needing to do these trials with 40,000 people that take a long time and a lot of expense to complete.

PALCA: So maybe they could use, say, 100 people and test their blood and be able to say, oh, yes, that's going to give us a similar outcome, instead of testing tens of thousands if they want to see if a vaccine is working.

SHAPIRO: Is there a specific antibody level that would tell scientists and regulators this vaccine is working if it reaches that level?

PALCA: Well, that would be great. But unfortunately, things are not that simple. David Benkeser from Emory University is another author on this study.

DAVID BENKESER: Unfortunately, the story's a bit more subtle than that. And so we really view this as being more of a continuum, that, you know, some antibodies good and more are better.

PALCA: So there is no magic number, but people have been assuming that antibodies are an important aspect of the immune response that's been protecting people from disease. So this is an important confirmation of that. But no magic number means - let's say you've been vaccinated, as I have. And I assume - and I want to get my blood tested to see if maybe my antibody levels have dropped. Well, no, you can't do that. The vaccines aren't - I mean, if I - do I need a booster shot? No, you can't tell that at this point because the data isn't that clear from these studies. But I would say that even - in fact, they discovered in this research paper that even people with undetectable antibodies still seem to have some amount of protection.

SHAPIRO: You said these were people who got the Moderna vaccine. Will results be the same for Johnson & Johnson and Pfizer?

PALCA: Well, you can't say for sure. But I think - and researchers are planning a similar study with the J&J vaccine and the AstraZeneca vaccine, as it happens, to make sure that these markers apply more universally to COVID vaccines and not just Moderna. But likelihood is they do, and that could be very useful going forward.

SHAPIRO: NPR's Joe Palca, thank you.

PALCA: You're welcome. Transcript provided by NPR, Copyright NPR.