Everything We Know (So Far) About Blood Clots and the Johnson & Johnson Covid-19 Vaccine

It’s too soon to know what specifically caused the blood clots — that’s the biggest reason the vaccine administration was paused

Tara Haelle
Elemental

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An illustration of the inside of a red blood vessel with a clump of red blood cells traveling through it.
Image by Mecder

The CDC and FDA jointly recommended pausing administration of the Johnson & Johnson Covid-19 vaccine Tuesday April 13, sending a lot of people into a tailspin of questions about what the suspension means and whether the vaccine is safe. Here’s an explainer that answers as many of those questions as carefully as is currently possible — no doubt more answers will come every day.

What happened?

On April 13, the FDA and CDC jointly announced a recommendation that administration of the Johnson & Johnson Covid-19 vaccine pause to allow investigation of a possible safety concern. Out of 6.8 million doses of the vaccine given so far in the U.S., six people experienced a rare blood clot in the brain along with a condition where the blood stops clotting effectively. (That sounds contradictory, but we’ll get to that in a bit.) One person with this blood clot died.

It’s worth noting that the nationwide administration of a highly effective vaccine has been halted in the midst of a deadly pandemic after a single…

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Tara Haelle
Elemental

Tara Haelle is a science journalist, public speaker, and author of Vaccination Investigation and The Informed Parent. Follow her at @tarahaelle.