COVID-19—the actual disease—poses 8 to 10 times the threat of blood clots in the brain than do coronavirus vaccines, a large, non–peer-reviewed study led by University of Oxford researchers finds.The study, published today on the preprint server OSF, involved an electronic health records network of 81 million patients at 59 healthcare systems, mainly in the United States.The researchers tallied patients diagnosed as having cerebral venous thrombosis (CVT) in the 2 weeks after they received either their COVID-19 diagnosis or their first dose of the Pfizer/BioNTech or Moderna vaccine from Jan 20, 2020, to Mar 25, 2021.