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Amid Blood Clot Concerns, U.S. Recommends Pausing Use Of J&J Vaccine


The FDA and the CDC have called for a pause in the use of the Johnson & Johnson coronavirus vaccine. There are reports that six women who got that vaccine developed blood clots afterward. NPR's Joe Palca is following this story. Good morning, Joe.

JOE PALCA, BYLINE: Good morning, Noel.

KING: What do we know about the blood clots themselves?

PALCA: Well, the news is just coming in. As you said, these were all among women. They were aged 18 to 48 and the symptoms that occurred occurred six to 13 days after they got the vaccination. And this is a rare kind of blood clot called a cerebral venous sinus thrombosis. And not only is it a rare form of thrombosis, but it also - this one occurs with something which is unusual, which is a low level of platelets or thrombocytopenia. And again, the symptoms of this are like a stroke - headache, blurred vision, fainting, loss of consciousness, loss of control over movement in a part of the body, seizures. And the distinction is that you can't - you have to be careful how you treat this because some blood clots you treat with blood thinners. You don't with this kind because of the low platelet levels.

KING: Oh, OK. Let me ask you then a follow. Blood clots were also reported in rare cases among people who got the AstraZeneca vaccine. Is this the same kind of blood clot?

PALCA: Yeah, apparently. I mean, it definitely is one of the ones they were seriously concerned about. And April 7 the European Medicines Agencies, their safety committee, which is called PRAC - P-R-A-C - has concluded that the unusual blood clots should be listed as a rare side effect of the AstraZeneca-Oxford vaccine. So, yes, they are seeing the same sort of thing. And it's a little disturbing.

KING: With the caveat that it is very early, is there something about these vaccines that is different from the Moderna and Pfizer vaccines that could be causing these blood clots?

PALCA: Right. There is. But first, as you say, these are - it is early days. These are extremely rare. And when the European Medicines Agency did its conclusion, it said, look, your chances of becoming sick and possibly dying from the virus are a lot greater than becoming sick and possibly dying from this particular kind of blood clot. But the interesting thing is that both the AstraZeneca and the Johnson & Johnson use a kind of delivery system called an adenovirus vector - doesn't matter exactly what they are, but that's different from Pfizer and Moderna, which doesn't use an adenovirus vector. And so that may be why we're seeing it in one and not the other. And in any case, it seems to be a rare something to do with the immune system that is occurring but only in a very few people. The problem is we don't know which of those very few people are the ones that you need to be careful with.

KING: Right.

PALCA: And so that's why they're trying to figure out as much as they can about who might be susceptible and what to do about it.

KING: OK. So let's talk about the figuring it out. There's going to be some sort of review, I imagine. Who will conduct the review? How will that work?

PALCA: Yeah, this is both the Food and Drug Administration and the Centers for Disease Control and Prevention. And the CDC announced that tomorrow the ACIP, which is their advisory committee on vaccine practices, will look into these reports and make its own conclusion about how or if they're related to the vaccines and if they are, what to do about it and whether it's safe to go forward with them.

KING: All right. So we will know more soon. NPR science correspondent Joe Palca. Thanks, Joe.

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

Joe Palca
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. From 2011 to 2020 he produced stories that explored the minds and motivations of scientists and inventors as part of his series, Joe's Big Idea. Palca is also the founder of NPR Scicommers – A science communication collective.