Back in March, several European nations paused use of the AstraZeneca vaccine based on concerns about case reports of blood clots in recently vaccinated individuals. The specific blood clots formed in several of the patients were a rare and dangerous type of clot known as cerebral venous sinus thrombosis (CVST), resulting in strokes and occasionally seizures in patients. Whether in the brain or elsewhere, these blood clots were especially unusual because they were associated with low platelets (a condition known as thrombocytopenia) and sometimes bleeding. Even more concerning, the specific blood clot formed in many of the patients was. The same phenomenon was later observed with the Johnson & Johnson vaccine, resulting in a pause in the US in mid-April. Interestingly, almost all of the cases were identified in younger females aged 18-48 (although one case in a younger man has since been reported, as well as an earlier male case during clinical trials).
