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What To Know About The Blood Clot Risks Associated With The Johnson & Johnson Vaccine


Concerns over extremely rare but serious blood clots have caused federal officials to recommend a pause on the Johnson & Johnson vaccines in the U.S. This as governments around the world are rethinking distribution of the AstraZeneca vaccine for the same reason. Dr. Menaka Pai is an associate professor of hematology at McMaster University in Ontario, Canada. She's also one of the province's scientific advisers on COVID-19. And she joins us now from Hamilton, Ontario. Welcome to the program.

MENAKA PAI: Hi there, Debbie. Nice to be with you.

ELLIOTT: So before we get into vaccines and blood clots, why don't we start by just having you tell us a little bit about the kinds of clotting you might normally see in your patients?

PAI: So in our body, we have arteries, and we have veins. And, actually, blood clots in those different areas aren't too uncommon. So whether they're heart attacks or strokes or blood clots in the legs, called DVTs, or blood clots in the lungs, called PEs, we kind of see it all.

ELLIOTT: Are some people more susceptible to clotting than others?

PAI: There are definitely factors that put people more at risk. So, for example, we know that women who have higher levels of estrogen just normally or whether they're on the pill or whether they're pregnant or postpartum - they're more susceptible. Older people are susceptible. And individuals who are ill or in hospital or who have just had a surgery - all of those things can push your risk of having a blood clot a little bit higher.

ELLIOTT: So at this point, we know more about the clotting cases that are linked to the AstraZeneca vaccine. But what can you tell us about the few cases that have now been documented with the Johnson & Johnson vaccine?

PAI: Well, right now, what we know is that of the over 7 million Johnson & Johnson shots that have been given in the U.S., there have been six cases of really unusual clotting reported. So all of these six cases happened in relatively younger women, and all of them involved blood clots in the brain, something that we call cerebral vein or cerebral sinus vein thrombosis.

ELLIOTT: Why do you think it is that this is showing up in younger women in particular? Do we know anything about what could be going on here?

PAI: One of the ways to look at this is that this vaccine may be associated with blood clotting. And if you are just, as a person, slightly at higher risk of clots, maybe this would sort of push you over the edge. But the other way to look at it is, in many jurisdictions, whether it's Johnson & Johnson or the AstraZeneca vaccine, it's been preferentially rolled out to younger women. So for example, in the EU, a lot of health care workers got the AstraZeneca vaccine, and those tend to be women under age 55. I'm telling my own patients that, right now, the numbers are really small - I mean, six cases and 7 million shots. So making a lot of assumptions about susceptibility can be a little risky. Those figures are pretty imprecise 'cause the numbers are so small.

ELLIOTT: So in the meantime, for people who may have gotten the J&J shot already and may be a little bit nervous and concerned about their own health, what should they be on the lookout for in terms of symptoms?

PAI: We know that these clots are an immune phenomenon, which means that they don't occur right after the shot. So if you get the shot and the next day you feel crummy, that's actually probably normal. But in the four to 20 days after a shot, whether it's AstraZeneca or Johnson & Johnson, if you start getting severe symptoms - so I mean a headache that doesn't go away, difficulties with your vision that are really interfering with your function, terrible chest pain, shortness of breath, swelling in a limb - these are symptoms that you would notice. And if that happens in that four-to-20-day window, it's really important to seek medical care. And then, you know, at this stage, I'm pretty confident in Canada and in the U.S. that doctors are aware of this condition, and we know how to spot it.

ELLIOTT: Now, what about people who might have those health conditions that we talked about earlier or take medications that could make them more susceptible to blood clots? What kinds of questions should they be asking? Where should they get information in terms of which vaccine they should get?

PAI: What we believe is that despite what we know about clot susceptibility, all of the standard things that put people at higher risk - for example, having a blood clot before or being on blood thinner medication - that doesn't seem to increase your risk of this immune phenomenon. So what we are telling our patients is take the first vaccine that's offered to you. But I do understand the fear. And it has been, you know, over 13 very hard months of worry. So I would suggest if somebody has questions about their own personal health condition, the best advocate, the best source of information is your own physician.

ELLIOTT: That's Dr. Menaka Pai, a hematologist at Hamilton Health Sciences in Ontario. Thank you for speaking with us.

PAI: Thank you, Debbie. Transcript provided by NPR, Copyright NPR.

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