Scientists Probe New Theories On Whether AstraZeneca Shot Linked To Blood Clots

European investigators have put forward one theory that the vaccine triggers an unusual antibody in some rare cases; others are trying to understand whether the cases are linked with birth control pills.

Scientists are exploring several possibilities that might explain at least 18 reports of extremely rare blood clots in the brain that occurred in individuals in the days and weeks after receiving the AstraZeneca COVID-19 vaccine. European investigators have put forward one theory that the vaccine triggers an unusual antibody in some rare cases; others are trying to understand whether the cases are linked with birth control pills. But many scientists say there is no definitive evidence and it is not clear whether or why AstraZeneca's vaccine would cause an issue not shared by other vaccines that target a similar part of the coronavirus. The European Medicines Agency said a preliminary review suggests the vaccine is not associated with an increase in the overall risk of blood clots. But it did not rule out an association with rare cases of blood clots in vessels draining the blood from the brain known as cerebral venous sinus thrombosis (CVST).