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AstraZeneca Chastised For For Using Outdated Data To Claim A Vaccine Efficacy Of 79%


What a difference a day makes. Yesterday, scientists celebrated AstraZeneca's announcement that its vaccine had an efficacy of 79% in preventing symptomatic COVID-19. Today, experts are criticizing the company for that very announcement. They say the company knew that 79% figure might be an overstatement. Here's White House COVID adviser Anthony Fauci, speaking today on "Good Morning America."


ANTHONY FAUCI: This is really what you call an unforced error because the fact is this is very likely a very good vaccine.

CORNISH: NPR science correspondent Joe Palca has been tracking the controversy and joins us now.

And Joe, I just want to follow up on what we heard from Dr. Fauci there. What else did he have to say about this company?

JOE PALCA, BYLINE: Well, this company is - you know, has created one of the COVID-19 vaccines that was one of the first out of the gate, and it's potentially coming to this country as well. But let me go back and tell you what this controversy is all about. It starts with something called a committee of the DSMB, the Data Safety Monitoring Board. These are - these big studies - in this case the AstraZeneca study was 32,000 - are blinded, which means the researchers don't know who's getting vaccine and the people getting the vaccine don't know if they're getting vaccine or a placebo. But somebody has to know, and that's the DSMB.

And the DSMB has certain stopping rules. So when they get a certain number of cases that indicate that the vaccine may be statistically evaluable, they stop the trial and they say - or at least they tell the company, you can now analyze the data. And so they did that a while ago.

And the company got the information, but apparently - and they did a report of what the results were, but apparently, they based their numbers on where the trial stood back in February. And the DSMB wanted them to report things where the trial stood in March because they want - there were more cases of COVID. And it appears that as more cases came out, the efficacy numbers went down. So the DSMB was concerned when they saw the press release, and they wrote to the federal officials who were co-sponsoring the study - including Tony Fauci - to complain that the company wasn't using the right numbers.


FAUCI: They felt that the data that was in the press release were somewhat outdated and might, in fact, be misleading a bit and wanted them to straighten it out.

CORNISH: What does the company say about this?

PALCA: Well, they put out a brief statement. And they said, yes, we used the February data, but that was a designated stopping point, so it was a reasonable place to start. But they agreed to go back to the DSMB and hash out their differences and promised to share a more up-to-date analysis with the public later this week.

CORNISH: Why is this disagreement over numbers so concerning?

PALCA: Well, for one thing, you've got to keep in mind that even though the study involved 32,000 people, the results are based on fewer than 200 cases of COVID. So, you know, you include a few more cases, a few fewer cases and your numbers or your statistics can change quite a bit. And, you know, a number matters. I mean, 30 - 79% doesn't sound as good as 95% and it sounds better than 65%. And Tony Fauci says it's confusing when the numbers seem to slosh around like this.


FAUCI: This kind of thing does nothing but really cast some doubt about the vaccines and maybe contribute to the hesitancy. It was not necessary.

PALCA: And AstraZeneca in particular has made a couple of stumbles, so they didn't need this controversy.

CORNISH: And what happens now?

PALCA: Well, the company says it's going to apply for an emergency use authorization. The FDA will scrutinize the data - I mean, really scrutinize the data now that there's this issue come up - and they'll make a decision about whether or not the emergency use authorization should be granted.

CORNISH: That's NPR science correspondent Joe Palca.

Thank you.

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

Joe Palca is a science correspondent for NPR. Since joining NPR in 1992, Palca has covered a range of science topics — everything from biomedical research to astronomy. He is currently focused on the eponymous series, "Joe's Big Idea." Stories in the series explore the minds and motivations of scientists and inventors. Palca is also the founder of NPR Scicommers – A science communication collective.