Rare blood clots tied to J&J’s COVID-19 shot are similar to issues with AstraZeneca’s vaccine, FDA official says

Federal health officials say the ultra-rare blood clots reported in six people who received Johnson & Johnson’s COVID-19 vaccine are similar to blood clots detected in a very small number of people in Europe who were immunized with AstraZeneca’s shot. 

The U.S. on Tuesday recommended pausing immunizations with J&J’s vaccine until further information is known about how to treat the blood-clotting disorder. 


stock was down 1.3% in after-hours trading Tuesday, with analysts at SVB Leerink noting that the “pause” weighed down shares.

Health officials said Tuesday they are combing through vaccine data to better understand why the blood clots are occurring, and the Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices is expected to hold an emergency meeting to discuss the J&J vaccine on Wednesday afternoon. The six cases in the U.S. were in women between the ages of 18 and 48.

The same analysts at SVB Leerink predict the committee will update its recommendations to say that the vaccine should no longer be given to women younger than 50. 

Women have been disproportionately affected by the condition, both with J&J’s vaccine as well as with AstraZeneca’s

in Europe, though the condition was also identified in some men there.

“If someone comes in with this really rather rare syndrome … the most common way to treat that is with heparin,” Dr. Anthony Fauci, President Joe Biden’s chief medical adviser, said during a White House briefing. “That would be a mistake in this situation because it could be dangerous and make the situation much worse. So there’s a clinically relevant reason why you want to make this known to people.”

The condition cited by Fauci is severe — one person has died in the U.S., and another is in severe condition, officials said — and also very rare, occurring in roughly one out of every 1 million people who have gotten the Johnson & Johnson shot. About 7.2 million people in the U.S. have received the J&J shot.

The blood-clotting disorder is called cerebral venous sinus thrombosis, and it was only reported in individuals who also had low levels of blood platelets, a condition called thrombocytopenia. 

“The real thing that is so notable here is not just the cerebral venous sinus thrombosis or the thrombocytopenia,” Dr. Peter Marks, director of the Food and Drug Administration’s Center for Biologics Evaluation and Research, said during a separate media briefing. “Those two things can occur. It’s their occurrence together that makes a pattern, and that pattern is very, very similar to what was seen in Europe.”

AstraZeneca’s vaccine, which was developed in partnership with the University of Oxford, is authorized in the U.K. and Europe, where health regulators in some countries have halted use of the vaccine due to rare reports of blood clots, primarily in women and occurring within the first weeks after vaccination. This is similar to the reports emerging in the U.S.  

The Johnson & Johnson and AstraZeneca COVID-19 vaccines are both adenovirus viral vector-based vaccines. J&J’s shot was authorized in the U.S. in February and in the European Union in mid-March, though the company said it now plans to  delay the rollout of its vaccine in Europe.

“It is a similar mechanism that may be going on with the other adeno viral-vectored vaccine,” Marks added. “That is, this is an immune response that occurs very, very rarely after some people receive the vaccine, and that immune response leads to activation of the platelets and these extremely rare blood clots.”

No thrombotic syndrome cases have been reported in people who have received either the Pfizer Inc.

or Moderna Inc.

mRNA vaccines, though there were earlier concerns about allergic reactions occurring in people who received those shots.  

J&J’s stock has gained 1.3% so far this year, while U.S.-listed shares of AstraZeneca are down 1.6%. The broader S&P 500

is up 9.9% for the year.

Related stories:

Johnson & Johnson vaccine pause: What to know if you got or scheduled the shot

Johnson & Johnson pause ‘will not have a significant impact on our vaccination plan,’ White House says

Moderna, BioNTech stocks surge after regulators halt use of J&J vaccine

U.S. COVID vaccine program faces setback with J&J jab, as experts say there is no cause for alarm

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