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What do we know about how the Johnson & Johnson vaccine is connected to cases of blood clots?

This article was published on
April 14, 2021

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SciLine reaches out to our network of scientific experts and poses commonly asked questions about newsworthy topics. Reporters can use these responses in news stories, with attribution to the expert.

SciLine reaches out to our network of scientific experts and poses commonly asked questions about newsworthy topics. Reporters can use these responses in news stories, with attribution to the expert.

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Expert Comments: 

Beth Kirkpatrick, MD

These events have only been seen in the U.S. following the Johnson & Johnson vaccines, not following either the Pfizer or Moderna vaccines. This appears to be associated with antibodies in the blood that are directed against platelets and cause both low platelets, which is associated with bleeding, and blood clotting.

Darryl Falzarano, PhD

There is an observation of rare coagulopathy (abnormal clotting) events that include low platelet levels following vaccination with the Johnson & Johnson AD26 vaccine. This situation appears to be similar to that observed with the AstraZeneca ChAdOx vaccine. The incidence rate, which appears to be between 1/250,000 to 1/1,000,000 seems to be comparable between both vaccines. Perhaps not surprisingly, given the low rate of occurrence, this has not been noted until millions of people have received these vaccines.

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