Skip to Content
Global News Select

Scientists Say They Found Cause of Rare Blood Clotting Linked to AstraZeneca Vaccine — 2nd Update

By Bojan Pancevski 

BERLIN -- Scientists in Europe said they had identified a mechanism that could lead the AstraZeneca PLC vaccine to cause potentially deadly blood clots in rare instances as well as a possible treatment for it.

Two teams of medical researchers in Norway and Germany have independently found that the vaccine could trigger an autoimmune reaction causing blood to clot in the brain, which would offer an explanation for isolated incidents across Europe in recent weeks.

Several European countries briefly halted their rollouts of the vaccine this week after more than 30 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 issue affected a tiny portion of those who had received the shot, however, and after investigating, the European drugs regulator ruled that the benefits outweighed the potential risks of the vaccine, and recommended vaccinations resume.

Some countries, such as Germany, France and Italy, resumed vaccinations with AstraZeneca's shot on Friday, with an added warning that it could be linked to blood clotting. The French healthcare authority, which recorded three cases of CVST connected to the vaccine, advised the government on Friday to only administer the shot to people older than 55.

Others, including Norway, Sweden and Denmark, said they needed more research before restarting their rollouts. Norway registered three cases of CVST, one of them fatal. The country vaccinated around 120,000 people with the shot. Finland suspended the use of AstraZeneca on Friday, after recording two cases of what the authorities called unusual blood clotting.

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

"Nothing but the vaccine can explain why these individuals had this immune response," Prof. Holme said.

Norway's health authority cited the findings when announcing that it wouldn't resume the vaccination.

A team of German researchers around Andreas Greinacher, professor of transfusion medicine at the Greifswald University Clinic, said Friday they had independently come to the same conclusion as Prof. Holme.

In Germany, 13 cases of CVST were detected among around 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 four days after vaccination, such as headaches, dizziness or impaired vision, could be quickly diagnosed with a blood test. Prof. Greinacher said the news meant that people shouldn't fear the vaccine.

"Very, very few people will develop this complication," Prof. Greinacher said in a press conference Friday. "But if it happens, we now know how to treat the patients."

He said that, after a swift diagnosis, the condition could be treated in any midsize hospital.

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

AstraZeneca declined to comment, pointing to a statement from Thursday in which it said that an analysis of tens of millions of its vaccination records didn't show that these events occurred any more frequently than would be expected in the general population.

Regulators in Germany, Austria and the Netherlands, where vaccinations using the AstraZeneca vaccine have either resumed or weren't suspended this week, didn't comment immediately. Britain's regulator, the Medicines and Healthcare Products Regulatory Agency, said it was aware of the findings in Germany and Norway and was collaborating with U.K. experts to establish whether similar findings could be made in the U.K.

"Given the extremely rare rate of occurrence of these CSVT events among the 11 million people vaccinated, and as a link to the vaccine is unproven, the benefits of the vaccine in preventing Covid-19, with its associated risk of hospitalization and death, continue to outweigh the risks of potential side effects," a spokeswoman for the agency said.

As a precautionary measure, the agency advises anyone with persistent headaches, or bruising beyond the site of vaccination after a few days, to seek medical attention.

The European Medicines Agency, or EMA, which regulates medicines for most European countries, said that it had assessed the cases from Germany and Norway and discussed them with the relevant national authorities.

A spokeswoman for EMA said that the vaccine may be associated with very rare cases of blood clots, including CVST, but that the benefits of the vaccine outweigh that risk.

"A causal link with the vaccine is not proven, but is possible and deserves further analysis," the spokeswoman said in a statement.

Neither the German nor the Norwegian findings were published or peer reviewed. Prof. Greinacher said he would submit his findings for publication to the British medical journal The Lancet in the coming days.

The German Society for Thrombosis and Hemostasis Research reviewed Prof. Greinacher's work and issued a statement Friday advising physicians how to diagnose and treat the condition should it arise in vaccine recipients.

Dr. Robert Klamroth, deputy chairman of the Society for Thrombosis and Hemostasis Research, said the rare autoimmune reaction occurred more frequently in Germany because the country initially only authorized the vaccine for people younger than 64. Britain, which had fewer incidents but vaccinated many more people, was predominantly giving the shot to older recipients.

Once diagnosed, the condition should be treated with blood thinning medication and immunoglobulin, which targets 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 is happening," Dr. Klamroth said.

On Friday, European leaders tried to alleviate potential concerns about the vaccine by lining up for the shot. The prime ministers of Britain and France, Boris Johnson and Jean Castex, were scheduled to receive the vaccine on Friday.

"I would take the AstraZeneca vaccine," German Chancellor Angela Merkel told reporters Friday. Ms. Merkel said she would wait until her turn came under Germany's prioritization schedule for vaccination.

Write to Bojan Pancevski at


(END) Dow Jones Newswires

March 19, 2021 16:17 ET (20:17 GMT)

Copyright (c) 2021 Dow Jones & Company, Inc.