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J&J scientists see little evidence of a link between Johnson & Johnson vaccine and blood clots

The J&J scientists said that out of 75,000 participants in a clinical trial, there was just one case of cerebral venous sinus thrombosis.

Jeff Lagasse, Associate Editor

(Photo by lechatnoir/Getty Images)(Photo by lechatnoir/Getty Images)

The Johnson & Johnson COVID-19 vaccine remains on pause due to concerns over several rare blood-clotting cases that have developed in a handful of people who have received the vaccine, but scientists writing in the New England Journal of Medicine have found scant evidence of a link.

The scientists, who work for Johnson & Johnson, said that out of 75,000 participants in a clinical trial, there was just one case of cerebral venous sinus thrombosis  a rare form of blood clot combined with low blood platelet counts. 

The scientists paused the trial to review the case and then resumed it when they could not establish causality.


The Centers for Disease Control and Prevention and the Food and Drug Administration recommended pausing the vaccine earlier this month and are reviewing the data independently. About 6.8 million doses of the Johnson & Johnson vaccine had been administered before the pause, and of those, six women developed blood clots.

One case was fatal, that of a 45-year-old woman with no risk factors who received the vaccine and developed cerebral venous sinus thrombosis with hemorrhage. All of the other five blood-clotting events were also reported in women between the ages of 18 and 48, with symptoms occurring six to 13 days after vaccination. 

Every state in the country has suspended the use of the J&J vaccine, and on April 14 an independent CDC advisory panel delayed making a recommendation for the vaccine's use so that it could gather more information on the blood-clot cases. The CDC panel will meet again later this week to provide guidance on the vaccine.

J&J scientists said in their letter that the blood clot cases "are occurring within the range of published background incidence," meaning they're occurring roughly at the normal rate of incidence among the general population. 

"We continue to work closely with experts and regulators to assess the data, and we support the open communication of this information to healthcare professionals and the public," the scientists wrote.


The trouble with the J&J vaccine began in early April, when vaccination sites in North Carolina and Colorado shut down temporarily after an abnormal number of adverse reactions to the vaccine.

Eleven people at a vaccine site at Dick's Sporting Goods in Commerce City, Colorado, experienced adverse side effects ranging from dizziness to nausea. The North Carolina site closed after patients there reported similar reactions.

At that time there was no reason to believe that there was anything wrong with the vaccine itself. Colorado public health officials said they found no sign of a problem with the single-dose offering.

Then the blood-clot cases occurred. While they're still considered extremely rare, the vaccine was put on hold, and federal officials stressed that there was more than enough supply of the Moderna and Pfizer vaccines to go around.

Health concerns for blood clots also exist for the AstraZeneca COVID-19 vaccine, which is not in use in the United States. Denmark said last week it will no longer use the AstraZeneca vaccine, not out of health safety concerns, but because it was not needed. That's because the country is in such an advanced stage of the vaccine rollout, according to CNN.

The European Medicines Agency found a possible link between the AstraZeneca COVID-19 vaccine and very rare cases of unusual blood clots with low blood platelets. But Barron's reported that research from the University of Oxford shows the Pfizer and Moderna vaccines also carry the rare blood-clotting risk.

Cerebral venous thrombosis developed in four in a million people who received those vaccines, the report said. This compares to five in a million people who developed blood clots after the first dose of AstraZeneca.

Twitter: @JELagasse
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