Scientists say the cause of rare blood clots has been linked to AstraZeneca vaccine

BERLIN – Scientists in Europe have said they have identified a mechanism that could lead to the AstraZeneca PLC vaccine, which in rare cases could cause potentially deadly blood clots, as well as a possible treatment for it.

Two teams of medical researchers in Norway and Germany have independently found that the vaccine can cause an autoimmune disorder that can cause blood to clot in the brain, which could provide an explanation for isolated incidents in Europe in recent weeks.

Several European countries briefly halted their deployment of the vaccine this week after more than thirty recipients were diagnosed with the condition known as cerebral venous sinus thrombosis or CVST. Most of the people affected were women under the age of 55.

The problem affected a small portion of those who received the shot, and after investigation, the European Drug Regulator ruled that the benefits outweighed the potential risks of the vaccine, and resumed the recommended vaccination.

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Some countries, such as Germany, France and Italy, resumed vaccination with AstraZeneca’s lap on Friday, warning that it was linked to blood clotting. The French health authority, which has recorded three cases of CVST linked to the vaccine, advised the government on Friday to administer the shot only to people over 55.

Others, including Norway, Sweden and Denmark, said they needed more research before starting again. Norway has registered three cases of CVST, one of which was fatal. The country vaccinated about 120,000 people with the shot. Finland suspended the use of AstraZeneca on Friday after recording two cases of what the authorities call unusual blood clotting.

Pål André Holme, a professor of hematology and chief physician at Oslo University Hospital, who was leading an investigation into the Norwegian cases, said his team had identified an antibody created by the vaccine that had the negative caused reaction.

The largest drug regulator in Europe endorses the vaccination of AstraZeneca after it was suspended in several countries due to blood clot disorders. WSJ explains what is at stake for a shot that is being used worldwide and that could soon be considered for emergency use in the US. Photo: Mykola Tys / SOPA Images

“Nothing but the vaccine can explain why these individuals had this immune response,” said prof. Holme said.

The Norwegian health authorities quoted the findings when announcing that they would not resume vaccination.

A team of German researchers around Andreas Greinacher, professor of transfusion medicine at Greifswald University Clinic, said they had independently reached the same conclusion as prof. Holme in a statement and a press conference Friday.

In Germany, 13 cases of CVST were detected among approximately 1.6 million people who received the AstraZeneca vaccine. Twelve patients were women and three died.

The German researchers, who coordinated with colleagues in Austria, Ireland and Britain, said in a statement that patients who show symptoms such as headaches, dizziness or visual impairment four days after vaccination can be diagnosed quickly with a blood test. Prof. Greinacher said the news means people should not fear the vaccine.

“Very, very few people will develop this complication,” said prof. Greinacher said at a news conference Friday. “But if that happens, we now know how to treat the patients.”

The team of Pål André Holme at the Oslo University Hospital identified an antibody created by the AstraZeneca vaccine that caused the negative reaction.


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Terje Pedersen / Associated Press

The German government said it was investigating the findings but stuck to the decision to resume use of the AstraZeneca vaccine.

Neither the German nor the Norwegian findings were published or judged by peers. Prof. Greinacher said he had submitted his findings for publication to the British medical journal The Lancet.

The German Association for Thrombosis and Hemostasis Research has published the work of prof. Greinacher reviewed and on Friday issued a statement advising doctors how to diagnose and treat the condition should it occur with vaccines.

Dr. Robert Klamroth, vice president of the Association for Thrombosis and Hemostasis Research, said the rare autoimmune reaction occurred more frequently in Germany because the country initially only granted the vaccine to people younger than 64. Britain, which has fewer incidents had, but vaccinated many. more people, were mainly giving the shot to older recipients.

Once diagnosed, the condition should be treated with blood thinner and immunoglobulin, which targets the antibody causing the problem.

“We believe that the most likely hypothesis is that this particular vaccine causes a rare autoimmune reaction that causes antibodies, which then interact with the platelets, but we do not know why this happens,” said Dr. Klamroth said.

Write to Bojan Pancevski by [email protected]

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