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.
Latest Vaccine Developments
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 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 would not resume the vaccination.
A team of German researchers around Andreas Greinacher, professor of transfusion medicine at the Greifswald University Clinic, said they had independently come to the same conclusion as Prof. Holme in a statement and a press conference on Friday.
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 should not 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 mid-sized hospital.
The German government said it was examining the findings, but stuck to its decision to resume use of the AstraZeneca vaccine.
AstraZeneca didn’t immediately react to a request for comment. Neither did the medicines regulators in Britain, Germany, Austria and The Netherlands, where vaccinations using the AstraZeneca vaccine have either resumed or weren’t suspended this week.
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 had submitted his findings for publication to the British medical journal The Lancet.
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.
Write to Bojan Pancevski at email@example.com
Copyright ©2020 Dow Jones & Company, Inc. All Rights Reserved. 87990cbe856818d5eddac44c7b1cdeb8