BERLIN – Scientists in Europe say they have identified a mechanism that could cause the AstraZeneca PLC vaccine to cause life-threatening blood clots in rare cases, as well as possible treatment for it.
Two teams of medical researchers from Norway and Germany have independently found that the vaccine could trigger an autoimmune reaction that would cause blood to clot in the brain, which would provide an explanation for the isolated incidents in Europe in recent weeks.
Several European countries have briefly stopped launching the vaccine this week after more than 30 patients 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.
However, the problem affected a small part of those who had received the shot and, after investigations, the European Medicines Authority decided that the benefits outweighed the potential risks of the vaccine and the recommended vaccinations were resumed.
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Some countries, such as Germany, France and Italy, resumed vaccination with AstraZeneca’s shot on Friday, with an added warning that it could be linked to blood clotting. The French healthcare authority, which has registered three cases of CVST connected to the vaccine, on Friday advised the government to administer the shot only to people over 55 years of age.
Others, including Norway, Sweden and Denmark, said they needed more research before resuming launches. Norway has three cases of CVST, one fatal. The country has vaccinated about 120,000 people with the shot. Finland suspended the use of AstraZeneca on Friday after registering two cases of what authorities called unusual blood clotting.
Pål André Holme, a professor of hematology and chief physician at Oslo University Hospital, who led an investigation into Norwegian cases, said his team had identified an antibody created by the vaccine that triggered the adverse reaction.
Europe’s top regulator has approved the AstraZeneca vaccine after it was suspended in several countries due to blood clot problems. WSJ explains what’s at stake for a photo that has been widely used around the world and 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.
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 had independently reached the same conclusion as Prof. Holme in a statement and a press conference on Friday.
In Germany, 13 cases of CVST were detected in approximately 1.6 million people who received the AstraZeneca vaccine. Twelve patients were women and three died.
German researchers, who coordinated with colleagues in Austria, Ireland and the United Kingdom, said in a statement that patients with symptoms four days after vaccination, such as headaches, dizziness or visual disturbances, could be diagnosed. fast with a blood test. Prof. Greinacher said the news means people should not be afraid of the vaccine.
“Very, very few people will develop this complication,” Prof. Greinacher told a news conference on Friday. “But if it happens, we now know how to treat patients.”
Pål André Holme’s team at Oslo University Hospital identified an antibody created by the AstraZeneca vaccine that triggered the side effect.
Photo:
Terje Pedersen / Associated Press
He said that after a quick diagnosis, the condition could be treated in any medium-sized hospital.
The German government has said it is examining the findings, but has stuck to its decision to resume using the AstraZeneca vaccine.
AstraZeneca did not immediately respond to a request for comment. Nor have the drug regulators in the UK, Germany, Austria and the Netherlands, where vaccinations using the AstraZeneca vaccine, either resumed or been suspended this week.
The European Medicines Agency or EMA, which regulates medicines for most European countries, said it had assessed the cases in Germany and Norway and discussed them with the competent national authorities.
An EMA spokeswoman said the vaccine could be associated with very rare cases of blood clots, including CVST, but that the benefits of the vaccine outweigh that risk.
“A causal link to the vaccine is not proven, but it is possible and deserves further analysis,” the spokesman said in a statement.
Neither German nor Norwegian findings have been published or evaluated by colleagues. Prof. Greinacher said he presented his findings for publication in the British medical journal The Lancet.
The German Society for the Research of Thrombosis and Hemostasis analyzed the activity of Prof. Greinacher and issued a statement on Friday advising doctors on how to diagnose and treat the condition if it occurs in patients receiving the vaccine.
Dr. Robert Klamroth, vice president of the Society for the Research of Thrombosis and Hemostasis, said that the rare autoimmune reaction occurred more frequently in Germany because the country initially only authorized the vaccine for people under 64 years of age. The UK, which had fewer incidents but vaccinated many more people, was predominantly giving older recipients.
Once diagnosed, the condition should be treated with blood thinners and immunoglobulin, which targets the antibody that is causing the problem.
“We think the most likely hypothesis is that this particular vaccine causes a rare autoimmune reaction that triggers antibodies, which then interact with platelets, but we don’t know why this happens,” said Dr. Klamroth.
Write to Bojan Pancevski at [email protected]
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