Higher risk of brain clots from Covid-19 compared with vaccines: study A woman receives an Oxford-AstraZeneca coronavirus disease (Covid-19) vaccine at a Covid-19 vaccination centre at Cwmbran Stadium in Cwmbran, South Wales, Britain February 17, 2021. Photo: Reuters Reuters Reuters There is a much higher risk of brain blood clots from Covid-19 infection than there is from vaccines against the disease, British researchers said on Thursday, after the rollout of inoculations was disrupted by reports of rare clots. AstraZeneca (AZN.L) and Johnson & Johnson (JNJ.N) have both seen very rare reports of cerebral venous sinus thrombosis (CVST) linked to their vaccines. On Wednesday, the United States paused vaccinations using J&J's shot while a link with clots was investigated, with Denmark ditching AstraZeneca's shot over the issue.