"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 independently have 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 fraction 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 inoculation, and recommended vaccinations resume.
Some countries, such as Germany, France and Italy, resumed vaccination with AstraZeneca's shot on Friday, with a 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 about 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.
Pal Andre 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 they independently came to the same conclusion as Prof. Holme.
In Germany, 13 cases of CVST were detected among 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 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," he said. "But if it happens we now know how to treat the patients."
The German government said it was examining the findings, but stuck to its decision to resume use of the 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 didn't comment." [1]
1. World News: Scientists Say They Found Cause of Rare Clotting Cases
Pancevski, Bojan. Wall Street Journal, Eastern edition; New York, N.Y. [New York, N.Y]20 Mar 2021: A.6.
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