Studies suggest link between blood clots, AstraZeneca COVID vaccine

Two studies today in the New England Journal of Medicine describe 11 patients in Austria and Germany and 5 in Norway who developed an unusual blood clotting disorder after receiving their first dose of the AstraZeneca/Oxford COVID-19 vaccine.

Clots form in brain, abdomen

The first study, led by researchers at the Institute for Immunology and Transfusion Medicine in Greifswald, Germany, involved 11 patients who had abnormal blood clots or thrombocytopenia (low platelet counts) 5 to 16 days after receiving the AstraZeneca vaccine.

One patient had a fatal intracranial hemorrhage (bleeding in the brain), while nine had cerebral venous thrombosis (blood clots in the brain), three had splanchnic vein thrombosis (blood clots in abdominal veins), three had a pulmonary embolism (blockage in a lung artery caused by blood clots), and four had other types of blood clots. Six patients, in addition to the patient with fatal intracranial hemorrhage, died.

Five patients had disseminated intravascular coagulation, a condition in which blood clots form in different parts of the body and block small blood vessels. No patients had received heparin to prevent blood clots before their symptoms began.

Twenty-eight patients from another sample referred for investigation of vaccine-induced abnormal blood clotting tested positive for heparin-induced platelet factor 4 (PF4) thrombocytopenia antibodies, independent of heparin. All of them also tested positive for platelet-activating antibodies.

Platelets are involved in the blood clotting process. The study authors said high levels of heparin, Fc receptor-blocking monoclonal antibody, and immunoglobulin inhibited platelet activation.


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