Researchers may have found trigger for brain clots potentially tied to AstraZeneca COVID-19 vaccine

Two research teams in Norway and Germany claim AstraZeneca's COVID-19 vaccine AZD1222 could trigger an autoimmune reaction that may have caused rare cases of potentially fatal blood clots in the brain. The teams, which separately came to the same conclusions, believe the mechanism would offer an explanation for isolated incidents of cerebral vein thrombosis (CVT) in recipients of the vaccine across Europe in recent weeks, and suggest there may be a possible treatment for it as well.

Haematologist Pål André Holme of Oslo University Hospital, who headed an investigation into cases reported in Norway, said his team identified an antibody created by AZD1222 that was triggering the adverse reaction. "Nothing but the vaccine can explain why these individuals had this immune response," he said.

Meanwhile, German researchers led by Andreas Greinacher from Greifswald University Clinic said Friday that they had independently come to the same conclusion as Holme and his team. Patients who show symptoms, such as headaches, dizziness or impaired vision, four days after vaccination could be swiftly diagnosed, according to Greinacher, with treatment consisting of anticoagulant medication and immunoglobulin that targets the antibody in question.

'We now know how' to treat the reaction

However, the German team, which also had cooperation from the country's Paul Ehrlich Institute, emphasised that treatment would only be possible in patients where blood clots appear, rather than as a preventative treatment. Still, Greinacher suggested the discovery means people should not fear AstraZeneca's vaccine, adding that "very, very few…will develop this complication, but if it happens, we now know how to treat the patients."

Robert Klamroth, deputy-chairman of the Society for Thrombosis and Hemostasis Research, suggested the rare autoimmune reaction occurred more frequently in Germany because the country initially only authorised AZD1222 for people under 64 years of age, whereas the UK had fewer incidents, even though it vaccinated many more people, likely because it was being given to older recipients. "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," Klamroth said.

Countries resuming vaccinations

Several countries, mostly in Europe, had temporarily suspended their rollouts of AZD1222 in the past week or so as they awaited the outcome of an investigation by the European Medicines Agency (EMA). In an update on March 18, the EMA concluded that the vaccine was safe and not associated with an overall higher risk of thromboembolic events. However, it could not conclusively rule out that the vaccine was behind rare instances of CVT as well as some cases of disseminated intravascular coagulation, adverse events that it said had occurred almost exclusively in women under the age of 55. The agency is continuing to look into the possibility of a causal link there, but in the meantime believes the benefits of AZD1222 in preventing COVID-19 far outweigh any risks.

Following the EMA's report, most countries including Germany, France and Italy, resumed vaccinations with AZD1222, although Norway's health authority cited Holme's findings when announcing that it would not do so. Researchers said they have shared the information with hospitals around Europe, although the findings have not yet been published or peer reviewed.

However, despite the EMA's report, some believe the side-effect concerns and subsequent suspensions by several governments will sway people against AZD1222, even as some EU countries are bracing for a third wave of infections. See ViewPoints: FirstWord survey says reputation of AstraZeneca’s COVID-19 vaccine at risk in Europe…


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