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Blood Clot Concerns Put Johnson & Johnson Vaccine On Pause


The effort to vaccinate as many Americans as possible ran into complications today. The Food and Drug Administration and the Centers for Disease Control and Prevention are calling for a pause in the use of Johnson & Johnson's COVID-19 vaccine. Now, this move comes after six women developed rare but serious blood clots, and one of them died. Here is acting FDA Commissioner Janet Woodcock speaking on a conference call this morning.


JANET WOODCOCK: Right now I'd like to stress these events appear to be extremely rare. However, COVID-19 vaccine safety is a top priority for the federal government.

KELLY: Joining us to talk about the vaccine pause is NPR science correspondent Joe Palca.

Hey, Joe.

JOE PALCA, BYLINE: Hey, Mary Louise.

KELLY: So when we hear Janet Woodcock there say these blood clots are extremely rare, how rare? Give us some context.

PALCA: Well, they - there have been 6.8 million doses of this vaccine administered and six cases of these rare blood clots. So that's not very common but more common than you would expect from people who never got the vaccine. So there seems possibly to be a link. And, of course, if you're one of those six, it's not a very good thing.

KELLY: No. How bad could this get? Is there any question, any chance the FDA will rescind authorization altogether to use this vaccine?

PALCA: I would say that's extremely unlikely. I think they're still looking at a significant risk of people getting sick and dying from COVID-19 versus this very small risk of getting one of these blood clots, which is - which are treatable in most cases. Or not - I don't know if it's most cases. It seems to be treatable. Let's put it that way.

KELLY: OK, rare and we think treatable - however, for people who were already not persuaded that they want a vaccine, for people who are not convinced yet, does this raise a red flag?

PALCA: You know, that's possible. The government is sort of in a difficult place. They're trying hard to be transparent, and it would be far worse if it turned out they knew about this risk and didn't tell anyone. And there's a practical reason to issue the pause. I spoke with Gow Arepally, a professor of medicine at Duke University, where she studies this particular kind of blood clots that seem to be involved with the vaccine. And she says if you treat these like more common blood clots, you can make the condition worse.

GOW AREPALLY: The main reason they wanted to alert clinicians is to make sure that people don't automatically reach for heparin because that is the most commonly used blood thinner for treating blood clot.

PALCA: Right. And it doesn't seem - it seems to have the opposite effect, or it could have the opposite effect with these clots. And there are other drugs that can be used.

KELLY: This sounds, Joe, awfully like the blood clots that we were hearing about with the AstraZeneca vaccine, the one so widely used in Europe. Are they similar?

PALCA: Yeah, very similar - and both AstraZeneca and Johnson & Johnson use something called an adenovirus vector in their vaccines. Moderna and Pfizer, on the other hand, don't use the adenovirus vector, and they don't see these particular kinds of problems.

KELLY: OK. If someone has already received the J&J vaccine, should they be worried?

PALCA: It's rare, but it's important to distinguish the reactions that people have immediately after getting the vaccine - sore arm and fatigue and such thing and feeling lousy. This is something different. Anand Padmanabhan is at the Mayo Clinic in Rochester, Minn. He also studies these rare blood clots. He says there are symptoms to watch out for.

ANAND PADMANABHAN: Leg pain, shortness of breath, headaches - so these are things - if you experience these in days or maybe even a couple of weeks after the shot, go to your doctor.

PALCA: And, again, Padmanabhan says there are treatments that seem to work for these clots.

KELLY: OK. NPR's Joe Palca, thanks for your reporting.

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

NPR transcripts are created on a rush deadline by an NPR contractor. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.

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.