Following reports of an unusual increase in cerebral sinus venous blood clots and one death associated with the COVID-19 vaccine developed by AstraZeneca and Oxford University, some countries halted its distribution. However, the World Health Organization (WHO) Director-General Tedros Adhanom Ghebreyesus, PhD, recommended continuing to administer the vaccine during a briefing on March 12.
Dr. Tedros said that the WHO's global advisory committee on vaccine safety is reviewing the reports of blood clots and plans to make its findings public.
"The safety of the public will always come first. We are keeping this issue under close review but available evidence does not confirm that the vaccine is the cause. People should still go and get their COVID-19 vaccine when asked to do so," said Phil Bryan, PhD, vaccines safety lead at Britain's Medicines and Healthcare Products Regulatory.
The Paul-Ehrlich-Institute (PEI), a German federal medical regulatory body, confirmed the positive benefit-risk ratio of AstraZeneca's vaccine. PEI experts observed rare cerebral sinus vein thrombosis in connection with thrombocytopenia and bleeding in temporal proximity to vaccinations with the AstraZeneca vaccine, amounting to 13 cases in more than 1.6 million vaccinated persons. Although rare, this cluster of very unlikely events was beyond statistical expectation. As a risk-mitigation warning, the summary of product characteristics includes the fact that in rare cases, specific thromboses are found up to 16 days after vaccination.
On March 19, researchers from the lab of Andreas Greinacher, MD, at the University of Greifswald in Germany, reported that they found evidence for an inflammatory response against platelet antigens similar to heparin-induced thrombocytopenia (HIT) occurring four to 16 days after vaccination. The German Society of Thrombosis and Hemostasis Research (GTH) issued a statement recommending that vaccinated individuals who develop headache, dizziness, or visual abnormalities more than three days after vaccination should immediately seek physician assistance. In addition, doctors are advised to investigate a complete blood count, D-dimers, and a peripheral blood film and refer patients to cerebral MRI. High-dose immunoglobulins may be the appropriate treatment to interrupt the immune activation of platelets via platelet factor 4.
The European Medicines Agency also released a statement in favor of continuing to administer the vaccine because its benefits "continue to outweigh its risks."