With news about blood clots linked to the Johnson & Johnson COVID vaccine causing quite a bit of alarm, I think it’s worth spending a bit more time looking into this, even after I wrote about clots and the AstraZeneca vaccine on Tuesday.
Based on public comments from Dr. Peter Marks, the head of center for biologics evaluation and research at the FDA, it appears that the blood clots related to the J&J vaccine are extremely similar to blood clots related to the AstraZeneca vaccine.
In case you didn’t read my newsletter from Tuesday, let’s catch up on some of the details:
The AstraZeneca vaccine seems to cause blood clots by activating a type of blood cell called platelets via an overactive immune system.
These blood clots are really dangerous. We’re seeing blood clots in the veins coming from the brain - terms cerebral sinus thrombosis - which has led to a number of vaccine-related deaths in young, healthy people.
Clotting events tend to happen 5 days to 14 days after vaccination.
This mechanism of clotting is very similar to a nasty reaction that we can see in some patients treated with a blood thinning medication called heparin. If you’re thinking that it’s odd have blood clots caused by a blood thinning medication - it is! And that’s part of why this is worrisome.
The numbers of patients we’re dealing with is super small. These vaccine side effects seem really, really rare.
The same signal isn’t present for the Moderna and Pfizer vaccines, which use a different mechanism of action (they are mRNA vaccines, rather than adenovirus vectors).
The news reports all lead with the same thing: these events are rare and the vaccines are safe the majority of the time
This is unequivocally true.
The J&J vaccine was noted to be linked to 6 blood clotting events in almost 7 million vaccine recipients. The AstraZeneca vaccine has been given to about 34 million people and there have been 222 blood clots reported (169 in the brain and 53 in the veins in the abdomen).
I’ve previously written about how effective the J&J vaccine is (and the AZ vaccine seems to be also, even if their trial was carried out in an amateurish manner).
But part of why we do post-trial surveillance of new treatments is because the signal for rare and dangerous side effects can be missed in a clinical trial.
So while I don’t intend to contradict the news reports or start fear-mongering, the signal for clotting wasn’t seen during the clinical trials and taking it seriously makes sense, even if there are very few events.
It’s worth thinking about why specifically these clots worry me, because they aren’t the same as regular blood clots.
Stop comparing these reactions to the concern about blood clots from birth control pills
I’ve seen plenty of reports - and received multiple questions from friends - about how the risk of getting a blood clot from birth control is much higher than getting one from the J&J vaccine.
That may be true, but all blood clots are not created equal.
Although you can get a blood clot in the brain from birth control, the most common type of blood clot that we see from estrogen-containing contraception is a deep venous thrombosis, or DVT. Occasionally this will lead to a pulmonary embolism, or blood clot in the lungs.
But a cerebral venous sinus thrombosis from birth control is extremely rare. And since it’s in the brain, it’s way, way more dangerous that a deep vein thrombosis.
The other reason that these clots are so different - the mechanism of clotting
These blood clots are caused by a similar mechanism of action as a medical condition called heparin induced thrombocytopenia (HIT).
This is problematic for two reasons:
The degree of blood stickiness (medical term: hypercoagulability) here is really high. HIT is one of the few medical conditions that causes blood clots in the arteries and not just the veins. When I think about HIT, I think about people who are really sick. I just don’t think about DVTs in the same way.
You don’t treat these blood clots with the same blood thinners that you treat normal blood clots with. We will frequently treat patients who have blood clots with heparin or heparin-related products. This makes the problem worse rather than better.
Because of reason number 2 - you don’t treat these blood clots with heparin because it makes things worse - it is vital to raise awareness about this rare vaccine-related side effect so that we can treat these patients appropriately.
And spreading the news that these clots generally occur 5-14 days after vaccination helps doctors spot the right patients and helps people seek care promptly if they have odd symptoms.
This news has changed my mind about the J&J vaccine
New information changes decision calculus.
I had previously suggested that J&J would be my vaccine of choice because it’s one shot and done and you don’t need to wait on a second dose. If it had been offered to me when I was vaccinated, I would have taken it. I would have advised my wife to get it if she was offered it.
Now I think it makes sense to wait for either Pfizer or Moderna.
Each decision with COVID is a risk/benefit analysis - masking, social distancing, opening school, going shopping, and even getting a vaccine.
Even though the absolute risk from the J&J vaccine is extremely low, the consequences of a clotting complication can be catastrophic and permanently devastating - which COVID can be too!
But if it’s possible to be more vigilant about avoiding COVID for a bit longer and it’s a question of getting J&J now or waiting a few weeks for Pfizer or Moderna, I would wait.
Your analysis might be different than mine if you have diabetes and heart disease and are going crazy from the social isolation, in which case the fastest road to immunity is the best one. In that case, taking the first available shot is a totally rational choice.
In other words, we can disagree here. While I would personally hold off on this vaccine right now, a reasonable person can look at the numbers here - 1 in a million shot - and think it’s worth going for despite the risks.
Vaccine hesitancy is real, and it’s concerning - but this was the right call
Of course there’s a concern that side effects from one vaccine have a spillover effect and make vaccine hesitancy worse, slowing down our march to herd immunity and increasing the chances of a variant emerging that can escape the vaccines.
But I think the FDA made the right call to pause this as we acquire more information.
Openness and transparency will lead to more trust in the process - and the vaccines - over the long haul, and so I think this was the right way to go.
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