Risk of blood clots in the brain due to COVID-19: disease and vaccination. Comments include information from a non-peer-reviewed study that has not yet been published


According to research from the University of Oxford, COVID-19 disease is associated with a much higher risk of
cerebral venous thrombosis than the risk from the COVID-19 vaccination with the Pfizer-BioNTech and Moderna
vaccines. Researchers used electronic records from large U.S. databases to compare the incidence of cerebral venous
thrombosis (CVT) in patients two weeks after being diagnosed with COVID-19, with patients two weeks after
receiving the vaccination. In 513,284 patients diagnosed with COVID-19, the incidence of CVT was 39.0 per million
people (confidence interval 95%: 25.2 to 60.2 per million). In the 489,871 patients receiving the vaccine, the
incidence was 4.1 per million (95% CI: 1.1 to 14.9 per million), for an adjusted relative risk of 6.36, with P<0.001.
The patients were vaccinated with the mRNA-based Pfizer-BioNTech or Moderna vaccine. Patients were not paired
by age or sex. The authors reported that the data did not indicate an obvious association between age/sex and
occurrences of CVT. It should be noted that the comparison was made with mRNA vaccines, not with viral vector

Thrombocytopenia associated with an immune response has been considered to be associated with occurrences of
CVT following vaccination with the AstraZeneca vaccine, specifically with antibodies to platelet factor 4, which
causes blood clotting and consumes platelets. These antibodies have been identified in patients who have
experienced blood clots. Thirty percent of cases of CVT due to COVID-19 occurred in patients under the age of 30.


  • Torjesen I. Covid-19: Risk of cerebral blood clots from disease is 10 times that from vaccination, study finds. BMJ
    2021; 373 :n1005 doi: 10.1136/bmj.n1005
  • Taquet M, Husain M, Geddes JR, Luciano S, Harrison PJ. Cerebral venous thrombosis: a retrospective cohort study of
    513 284 confirmed COVID-19 cases and a comparison with 489 871 people receiving a COVID-19 mRNA vaccine.
    OSF. doi: 10.17605/OSF. IO/H2MT7
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