What Do We Know About Blood Clots and COVID-19 Vaccine?

In this short video, Dr. Paul Offit discusses the blood clotting condition a few people have experienced following receipt of the Johnson & Johnson COVID-19 vaccine and what is known about the risk for individuals.


What do we know about blood clots and COVID-19 vaccine?

Paul Offit, MD: Hi, my name is Paul Offit. I'm talking to you today from the Vaccine Education Center at the Children's Hospital of Philadelphia. It's Wednesday, May 12th, 2021. So probably a question that's come up recently is, what's the story with blood clots and these COVID-19 vaccines? Well, first of all, the two messenger RNA vaccines, those made by Pfizer and Moderna, don't increase the risk of blood clots, so that's good. But the more recent vaccine, the so-called Johnson & Johnson vaccine, which is a replication defective adenovirus vector vaccine, does appear to be a rare cause of blood clots, including serious blood clots. And by serious blood clots, I mean a blood clot of the brain that has the name cerebral venous sinus thrombosis, or CVST. It's rare. It occurs in about 1.9 per million people who get this. It's more common in younger people, especially more common in younger women. So that is truly a real, but rare side effect. Now, you should also note that the virus SARS-CoV-2 also causes blood clots. It also causes the brain blood clots, the so-called CVST, at a rate of 5 to 6 per million. So, you're actually more likely to have that particular blood clot if you get infected with the virus than if you get the vaccine. But again, it is understandable how a young, especially a young woman, could reasonably say that I really would prefer the mRNA vaccines because they don't have this rare side effect.

Thank you.

Related Centers and Programs: Vaccine Education Center

Last Reviewed on Jun 01, 2021