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Results Of Coronavirus Vaccine Trial Questioned After AstraZeneca Admits A Mistake


At first, it all seemed like good news. On Monday, the drug company AstraZeneca and its partner, the University of Oxford, announced an experimental COVID-19 vaccine was 70% effective in preventing the disease. But as the week wore on, questions began to surface about how reliable that result was. Joining us now to discuss some of the issues that have come up is NPR science correspondent Joe Palca. Hi, Joe.


SHAPIRO: So what's the problem? Explain why that 70% figure might not be reliable.

PALCA: Well, it's probably accurate in terms of a number, but part of the reason, at least for now, is the company hasn't said a lot about how they arrived at that number. But one thing does seem to be clear - that instead of doing a simple study involving two groups, where one group got two injections of a vaccine and the other group got two injections of a placebo, and then you compare the groups, they had different - a lot of different groups with different doses, carried out in parts of different studies. And that makes it really hard to interpret the results.

SHAPIRO: Before we dig deeper into that, Pfizer and Moderna also reported good results for their COVID vaccines. Are these likely to also come under scrutiny?

PALCA: Well, they're certainly going to be scrutinized - very carefully, I should say - but they did do things in a more straightforward way. There were two groups. One got the vaccine, one got the placebo. And in both cases, they showed more than 90, almost 95% efficacy. Although, again, I have to say that almost all of what we know about the Pfizer, Moderna results and also the AstraZeneca-Oxford results is - comes from press releases. So scientists have a lot of questions that they don't have answers to, like who benefited the most from the vaccine, what age groups, what genders, what kinds of underlying conditions made a difference. So a lot of questions still.

SHAPIRO: All right. So to go back to the AstraZeneca-Oxford vaccine with this complicated design of the test, the results showed 70% efficacy, as we said. But I remember in your first report on the subject, you said for some groups, it was 90% effective if they got half a dose. Is that right?

PALCA: Yeah.

SHAPIRO: How did that work?

PALCA: (Laughter) Well, that's one of the really strange things, and it's one of the things that's raising scientific eyebrows. The vaccine is given in two injections, and a subset of patients wound up getting a half dose in the first injection and a full dose in the second injection. And that group actually did better - around 90% protection. So Mene Pangalos, who is the executive vice president for biopharmaceuticals and R&D at AstraZeneca, said at a news conference that the company said, oh, we're going to use that to suggest making changes to a large study that's underway in this country and include a group that gets the half-dose, full-dose regimen.


MENE PANGALOS: We will try and do that as quickly as possible. We need to have, I will say, a change in the protocol. We need to have a conversation with the FDA. But I would put that in a matter of weeks in terms of how quickly we could do that and get initiated.

SHAPIRO: So it sounds like they're getting more data, making adjustments. Why the raised eyebrows? What's wrong with that?

PALCA: Well, as you said, it's not immediately clear why a half-dose, full-dose regimen would work better than a full-dose, full-dose regimen. And it's also unclear exactly why they even tried a half-dose, full-dose in the first place. And the answer seems to be that it was a mistake in calculating the intended dose. Now, a mistake might have turned out OK, but you don't want to make mistakes like that when you're testing a new vaccine.

SHAPIRO: Yeah. And if we have these two other vaccines that seem to be successful, does it matter if the AstraZeneca-Oxford vaccine is stumbling a bit?

PALCA: Well, yes. In one sense, it does. I mean, in many senses, it would be nice. We're going to need a lot of different vaccines, I think. Most scientists agree with that. But globally, people had high hopes - or have high hopes for this vaccine because it's cheaper, it's easier to make, and it doesn't require any kind of special storage, which makes it much easier to distribute in low-resource countries.

SHAPIRO: That's NPR science correspondent Joe Palca. Thanks, Joe.

PALCA: You bet.


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.