Using  an  electronic  health  records  network  we  estimated  the  absolute  incidence  of  cerebral  venous thrombosis  (CVT)  in  the  two  weeks  following  COVID-19  diagnosis (N=513,284), or  influenza (N=172,742), or  receipt  of  the  BNT162b2  or  mRNA-1273  COVID-19  vaccines (N=489,871). The incidence of portal vein thrombosis (PVT) was also assessed in these groups, as well asthe baseline CVT incidence over a two-week period. The incidence of CVT after COVID-19 diagnosis was 39.0 per million people (95% CI, 25.2–60.2). This was higher than the CVT incidence after influenza (0.0 per million people, 95% CI 0.0–22.2, adjusted RR=6.73, P=.003) or after receiving BNT162b2 or mRNA-1273 vaccine (4.1 per million people, 95% CI 1.1–14.9, adjusted RR=6.36, P<.001). The relative risks were similar if a broader definition of CVT was used. For PVT, the incidence was 436.4 per million people  (382.9-497.4)  after  COVID-19,  98.4  (61.4-157.6)  after influenza, and 44.9  (29.7-68.0)  after BNT162b2 or mRNA-1273. The incidence of CVT following COVID-19 was higher than the incidence observed across the entire health records network (0.41 per million people over any 2-week period). Laboratory test results, availablein a subsetof the COVID-19 patients, provide preliminary evidence suggestive of raised D-dimer,  lowered  fibrinogen,  and  an  increased  rate  of  thrombocytopenia  in  the CVT and PVT groups. Mortality was 20% and 18.8% respectively. These data show that the incidence of CVT is significantly increased after COVID-19,andgreater than that observed with BNT162b2 and mRNA-1273 COVID-19 vaccines. The risk of CVT following COVID-19 is also higher than the latest estimate from the European Medicines Agency for the incidence associated with ChAdOx1 nCoV-19 vaccine (5.0 per million people, 95% CI 4.3–5.8). Although requiring replication and corroboration, the present data highlight the risk of serious thrombotic events in COVID-19, and can help contextualize the risks and benefits of vaccination in this regard.

COVID-19 and cerebral venous thrombosis: a retrospective cohort study of 513,284 confirmed COVID-19 cases