On Apr. 15, 2021, researchers at the University of Oxford reported that the risk of the rare blood clotting known as cerebral venous thrombosis (CVT) following COVID-19 infection is around 100 times greater than normal, several times higher than it is post-vaccination or following influenza.

They reported that CVT is more common after COVID-19 than in any of the comparison groups, with 30% of these cases occurring in the under 30s.