Scientists say they found a cause of rare blood clotting related to the AstraZeneca vaccine

Several European countries briefly stopped the launch of the vaccine this week after more than 30 recipients were diagnosed with the disease known as cerebral venous thrombosis or CVST. Most of the people affected were women under 55 years of age.

The problem affected, however, a small proportion of those who had received the shot and, after investigating it, the European Medicines Regulator decided that the benefits outweighed the potential risks of the vaccine and the recommended vaccinations were resumed. .

Some countries, such as Germany, France and Italy, resumed vaccination with AstraZeneca shooting on Friday, with an added warning that it could be related to blood clotting. The French health authority, which registered three cases of CVST related to the vaccine, on Friday advised the government to only administer the vaccine to people over 55 years of age.

Others, including Norway, Sweden and Denmark, said they needed more research before restarting the launches. Norway recorded three cases of CVST, one of them 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 authorities called an unusual blood clotting.

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

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

The Norwegian health authority cited the findings when it announced it would not resume vaccination.

A team of German researchers around Andreas Greinacher, a professor of transfusion medicine at the Greifswald University clinic, said they came to the same conclusion independently as Professor Holme in a statement and a press conference on Friday .

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

German researchers, who coordinated with colleagues from Austria, Ireland and Britain, said in a statement that patients who experience symptoms four days after vaccination, such as headaches, dizziness or altered view, they could be diagnosed quickly with a blood test. Professor Greinacher said the news meant people should not be afraid of the vaccine.

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

The German government said it was examining the results, but persisted in its decision to resume use of the AstraZeneca vaccine.

Neither the German nor the Norwegian conclusions were published or peer-reviewed. Professor Greinacher said he had presented his findings for publication in the British medical journal The Lancet.

The German Society for Research in Thrombosis and Hemostasis reviewed the work of Professor Greinacher and issued a statement on Friday advising doctors on how to diagnose and treat the disease in case it occurs in vaccine recipients.

Dr. Robert Klamroth, vice president of the Society for Thrombosis and Hemostasis Research, said the rare autoimmune reaction occurred more frequently in Germany, as the country initially only authorized the vaccine for people under 64 years of age. Britain, which had fewer incidents but vaccinated many more people, was primarily targeting the larger recipients.

Once diagnosed, the condition must be treated with anticoagulant drugs and immunoglobulin, which are directed to the antibody that causes the problem.

“We believe the most likely hypothesis is that this particular vaccine is causing a rare autoimmune reaction that triggers antibodies, which then interact with the platelets, but we don’t know why this happens,” Dr. Klamroth.

Write to Bojan Pancevski to [email protected]