From the Journals

AstraZeneca COVID vaccine: Clotting disorder mechanism revealed?


EMA data to date

Updated data, reported at the EMA press briefing on March 31, indicate that 62 cases of CVST have been reported worldwide (44 from the European Union). These data may not yet include all the German cases.

Peter Arlett, MD, head of pharmacovigilance and epidemiology at the EMA, said there were more cases than expected in the 2-week window after vaccination among patients younger than 60 and that health care professionals should be alert to features of this condition, including headache and blurred vision.

He suggested that the higher rate of the condition among younger women may reflect the population that received this vaccine, because initially, the vaccine was not recommended for older people in many countries and was targeted toward younger health care workers, who were mainly women.

The German regulatory agency, the Paul Ehrlich Institute, reported this week that it has now registered 31 cases of CVST among nearly 2.7 million people who had received the vaccine in Germany. Of these patients, 19 also were found to have a deficiency of blood platelets or thrombocytopenia. Nine of the affected patients died. All but two of the cases occurred in women aged 20-63 years. The two men were aged 36 and 57 years.

These data have prompted the German authorities to limit use of the AstraZeneca vaccine to those aged 60 years and older. Even before this decision, senior clinicians in Germany had been urging a change in the vaccination recommendations.

For example, Bernd Salzberger, MD, head of infectious diseases, University Hospital Regensburg (Germany), told the Science Media Center: “In women, a complicated course of COVID disease is less common from the start and is so rare in younger women that the chance of avoiding a fatal course through vaccination in women without comorbidities is of the same order of magnitude as the risk of this rare side effect.”

Sandra Ciesek, MD, a virologist at Goethe University, Frankfurt, Germany, told the journal Science: “The argument I keep hearing is that the risk-benefit ratio is still positive. But we do not have just one vaccine, we have several. So, restricting the AstraZeneca vaccine to older people makes sense to me, and it does not waste any doses.”

Concerns put in perspective

Commenting of the latest developments, thrombosis expert Saskia Middeldorp, MD, head of internal medicine at Radboud University Medical Center, Nijmegen, the Netherlands, said it was vitally important that these concerns be put in perspective and that the vaccination program with the AstraZeneca product continue.

“There are some concerning reports about very rare blood clotting disorders and low platelet counts possibly associated with the AstraZeneca vaccine. Groups from Germany and Norway have identified a syndrome similar to HIT, which seems to explain the cause of this very rare side effect,” Dr. Middeldorp noted.

“But with such a high pressure from the virus and many countries now going into a third wave of infection, anything that might slow down vaccination rates will cause much more harm than good,” she warned.

Dr. Middeldorp believes the incidence of this HIT-type syndrome linked to the vaccine is about 1-2 per million. “These are estimates based on the number of reports of this side effect and denominators from the U.K. and EU populations,” she explained. However, Germany has restricted the vaccine on the basis of German data, which appear to show higher rates of the condition. It is not known why the rates are higher in Germany.

“The European Medicines Agency is looking at this very closely. Their statement is quite clear. There is no foundation for changing policy on vaccination,” Dr. Middeldorp stated.

She cautioned that these reports were reducing confidence in the AstraZeneca vaccine, particularly among young people, which she said was causing “a major setback” for the vaccination program.

Noting that everything must be viewed in the context of this severe pandemic, Dr. Middeldorp emphasized that the benefit of the vaccine outweighed any risk, even among young people.

“To those who may be hesitating to have the vaccine as they don’t think they are at high risk of severe COVID infection, I would say there are a lot of young people in the ICU at present with COVID, and your chance of a severe COVID illness is far higher than the 1 or 2 in a million risk of a severe reaction to the vaccine,” she stated.

Dr. Greinacher has received grants and nonfinancial support from Aspen, Boehringer Ingelheim, Merck Sharp & Dohme, Bristol-Myers Squibb, Paringenix, Bayer Healthcare, Gore, Rovi, Sagent, and Biomarin/Prosensa; personal fees from Aspen, Boehringer Ingelheim, Merck Sharp & Dohme, Macopharma, Bristol-Myers Squibb, Chromatec, and Instrumentation Laboratory; and nonfinancial support from Boehringer Ingelheim, Portola, Ergomed, and GTH outside the submitted work.

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