NOEL KING, HOST:
A major coronavirus vaccine trial has been put on hold. AstraZeneca, the company developing the vaccine along with the University of Oxford, says a participant in the trial had a, quote, "potentially unexplained illness." With me now, Dr. Paul Offit. He's the director of the Vaccine Education Center at Children's Hospital of Philadelphia. Good morning, sir.
PAUL OFFIT: Good morning.
KING: How unusual is it for something like this to happen during a vaccine trial?
OFFIT: It's not common, but it's certainly not unheard of. It does happen when, presumably, someone had a serious adverse event soon after receiving the vaccine. And then the company just stops, takes a much closer look at that particular case to try and answer the question, was this a coincidental association or was it a causal association?
KING: With the caveat that I do not know anything about vaccines, how is it that the illness of one person - even if it's a serious illness - of a single person temporarily shuts down the whole trial?
OFFIT: Well, I mean, if this vaccine causes a rare-but-serious problem, I mean, you need to take a close look and really determine that before you move forward because if you move forward and it was a causal association, and then other cases occur similar to that, then you've done harm. So I think it's prudent of this company to do what they're doing - stop, take a much closer look at this case and try and answer the question, was this because of the vaccine?
You know, the COVID-19 vaccines are designed to prevent COVID-19 disease, not everything else that happens in life. So there - because - sometimes serious medical problems occur in adults. This is not unusual for something like that to happen. But you really do need to do what they're doing - stop, take a hard look at this case and try and answer the question, did the vaccine do this?
KING: OK. No, that makes complete sense. Do we know how many people were in this trial?
OFFIT: I think that the goal of this trial was to move to at least 30,000 people, where, presumably, say, 15,000 or 20,000 would get the vaccine, 15,000 or 20,000 would get the placebo. And so I presume they - the company knows that this was a vaccine recipient. And they'll look closely and see what they find.
KING: The vaccine is in late-stage trials - this particular one - in the U.S., in Brazil and South Africa. That's a lot of different countries involved. What does a halt mean for the whole effort? Does it derail it?
OFFIT: It depends. I mean, it depends on what they find. I mean, if - let's suppose, for example, someone had a heart attack within two days of getting the vaccine. Could the vaccine have done it? Biologically, that's not particularly plausible. And let's suppose you take a harder look at the case and you find out that this person was known to have, say, blockage of a coronary artery even before he got the vaccine. So that's reassuring that it wasn't the vaccine.
On the other hand, if it was an immunological problem, knowing that the - what vaccines do is they stimulate your immune response, then it's a matter of taking a harder look and saying, could the vaccine have done this? So that is more biologically plausible. So we'll see.
KING: Dr. Paul Offit is director of the Vaccine Education Center and an attending physician in the Division of Infectious Diseases at Children's Hospital of Philadelphia. Sir, thanks for being with us.
OFFIT: Thank you. Transcript provided by NPR, Copyright NPR.