EXPLAINER: What's known about J&J's vaccine and rare clots
4/12/21
The U.S.
recommended that states pause giving the J&J vaccine on Tuesday while authorities examine six reports of the unusual clots, including a death, out of more than 6.8 million Americans given the one-dose vaccination so far.
But the small number of cases sparked concern because just last week, European authorities said similar clots were possibly linked to the AstraZeneca vaccine, which is not yet OK’d in the U.S. That led some countries to limit its use to certain age groups.
Also Tuesday, J&J delayed its imminent
European rollout.
WHAT MAKES THESE CLOTS DIFFERENT?
These are not typical blood clots. They’re weird in two ways.
First, they’re occurring in unusual parts of the body, such as veins that drain blood from the brain. Second, those patients also have abnormally low levels of platelets -- cells that help form clots -- a condition normally linked to bleeding, not clotting.
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WHY SUSPECT IMMUNE RESPONSE?
The first clue: A widely used blood thinner named heparin sometimes causes a very similar side effect. Very rarely, heparin recipients form antibodies that both attack and overstimulate platelets, said Dr. Geoffrey Barnes, a clot expert at the University of Michigan.
“It kind of can cause both sides of the bleeding-clotting spectrum,” Barnes said.
Because heparin is used so often in hospitals, that reaction is something “that every hospital in America knows how to diagnose and treat.”
There also are incredibly rare reports of this weird clot-low platelet combination in people who never took heparin, such as after an infection. Those unexplainable cases haven’t gotten much attention, Barnes said, until the first clot reports popped up in some AstraZeneca vaccine recipients.
Health officials said one reason for the J&J pause was to make sure doctors know how to treat patients suspected of having these clots, which includes avoiding giving heparin.
