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Study: COVID much more likely than vaccines to cause blood clots

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. The researchers then compared those with rates of CVT in an unmatched cohort who had the flu and in the general population over the same period.
Only 2 cases in vaccinees

The risk of CVT was 8 to 10 times higher in the 513,284 patients with a COVID-19 diagnosis than in the 489,871 vaccinees and 100 times greater than in the general population. There were only two cases of CVT in the vaccine population, one after vaccination with the Pfizer vaccine and one after receipt of an undetermined mRNA vaccine. Patients younger than 30 years accounted for 30% of coronavirus-related CVT. The rate in the 172,742 flu patients was 0 per 1 million.

CVT in all patient groups was rare, at 39 per 1 million COVID-19 patients and 4 in 1 million vaccine recipients. The risk of CVT after COVID-19 was about 10 times higher than those from a single dose of the Pfizer or Moderna vaccines and, according to the European Medicines Agency (EMA), about eight times higher than after the AstraZeneca/Oxford vaccine. (The researchers couldn't ascertain this in the study population because this vaccine is not in use in the United States.)

The death rate among COVID-19 patients was 20% for those who had CVT and 18.8% for portal vein (liver) thrombosis (PVT), which was assessed in the same populations.

The incidence of PVT was 436.4 per 1 million people with COVID-19, 98.4 per 1 million among flu patients, and 44.9 per 1 million after vaccination with the Pfizer or Moderna vaccine. Twenty-two cases of PVT were diagnosed among vaccinees, 11 after the Pfizer vaccine, 2 after the Moderna vaccine, and 9 after a vaccine of an undetermined brand (either Pfizer or Moderna).

https://www.cidrap.umn.edu/news-perspective/2021/04/study-covid-much-more-likely-vaccines-cause-blood-clots