What is cerebral venous sinus thrombosis?

Coronavirus

The U.S. is recommending a pause in distribution of the Johnson & Johnson COVID-19 vaccine to allow health officials to investigate reports of rare but potentially dangerous blood clots called cerebral venous sinus thrombosis.

As of April 12, more than 6.8 million doses of the Johnson & Johnson vaccine have been administered. In six cases, a type of blood clot called cerebral venous sinus thrombosis (CVST) was seen in combination with low levels of blood platelets.

All six cases involved women between the ages of 18 and 48, and their symptoms occurred between six and 13 days following their vaccines. One person died, and all of the cases remain under investigation.

The clots occurred in veins that drain blood from the brain and occurred together with low platelets, the fragments in blood that normally form clots. 

FDA officials emphasized that Tuesday’s action was not a mandate. Doctors and patients could still use J&J’s vaccine if they decide its benefits outweigh its risks for individual cases, said Dr. Peter Marks.

The agencies recommend that people who were given the J&J vaccine should contact their doctor is they experience severe headache, abdominal pain, leg pain, or shortness of breath within three weeks.

J&J said in a statement that it was aware of the reports of blood clots, but that no link to its vaccine had been established. The company also said it would delay the rollout of its vaccine in Europe as a precaution.

U.S. health authorities cautioned doctors against using a typical clot treatment, the blood-thinner heparin. “In this setting, administration of heparin may be dangerous and alternative treatments need to be given,” the FDA and CDC said.

“Right now, these adverse events appear to be extremely rare. COVID-19 vaccine safety is a top priority for the federal government, and we take all reports of health problems following COVID-19 vaccination very seriously,” the FDA and CDC said. “People who have received the J&J vaccine who develop severe headache, abdominal pain, leg pain, or shortness of breath within three weeks after vaccination should contact their health care provider.”

European authorities investigating the AstraZeneca cases have concluded clots appear to be similar to a very rare abnormal immune response that sometimes strikes people treated with heparin, leading to a temporary clotting disorder.

While it’s not clear yet if the reports among J&J recipients are related, doctors would treat these kinds of unusual clots like they treat people who have the heparin reaction — with different kinds of blood thinners and sometimes an antibody infusion, said Dr. Geoffrey Barnes, a clot expert at the University of Michigan.

As authorities investigate whether the clots really are related to the J&J vaccine, Barnes stressed that Americans should get vaccinated as soon as possible using the other two available vaccines, from Pfizer and Moderna.

“If you have a chance to get vaccinated with those, we strongly encourage it. The risks of COVID are real and they’re high,” Barnes said.

Jeff Zients, the White House COVID-19 response coordinator, said 28 million doses of the Pfizer and Moderna vaccines will be available for states this week, more than enough to keep up the nation’s pace of 3 million shots a day despite the J&J pause.

Asked if the government was overreacting to six cases out of more than 6 million vaccinations, Schuchat said recommendations will come quickly.

Because these unusual clots require special treatment, “it was of the utmost importance to us to get the word out,” she said. “That said, the pandemic is quite severe and cases are increasing in lots of places and vaccination’s critical.”

States and cities swiftly moved to implement the pause. New York state Health Commissioner Dr. Howard Zucker said people with Tuesday appointments for J&J vaccines at state-run mass vaccination clinics will instead get the Pfizer vaccine.

The city of Dallas had planned to begin an in-home vaccination program using the J&J vaccine for homebound or elderly people. The city said it will pause the program until more guidance is released.

The J&J vaccine received emergency use authorization from the FDA in late February with great fanfare. Yet the shot only makes up a small fraction of the doses administered in the U.S. J&J has been plagued by production delays and manufacturing errors at the Baltimore plant of a contractor.

Last week, the drugmaker took over the facility to scale up production in hopes of meeting its commitment to the U.S. government of providing about 100 million doses by the end of May.

Only about 9 million of the company’s doses have been delivered to states and are awaiting administration, according to CDC data.

Until now concern about the unusual blood clots has centered on the vaccine from AstraZeneca, which has not yet received authorization in the U.S. Last week, European regulators said they found a possible link between the shots and a very rare type of blood clot that occurs together with low blood platelets, one that seems to occur more in younger people.

The European Medicines Agency stressed that the benefits of receiving the vaccine outweigh the risks for most people. But several countries have imposed limits on who can receive the vaccine; Britain recommended that people under 30 be offered alternatives.

But the J&J and AstraZeneca vaccines are made with the same technology. Leading COVID-19 vaccines train the body to recognize the spike protein that coats the outer surface of the coronavirus. But the J&J and AstraZeneca vaccines use a cold virus, called an adenovirus, to carry the spike gene into the body. J&J uses a human adenovirus to create its vaccine while AstraZeneca uses a chimpanzee version.

U.S. stock markets initially dropped on the J&J news, but some indices were up slightly by late morning. Johnson & Johnson shares were down nearly 3 percent, an unusually big drop for the drug giant, with more shares changing hands in the first two hours than on an average day.

The Associated Press contributed to this story.

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