evidence: By — Matthew Herper, STAT News Matthew Herper, STAT News Leave a comment 0comments Share Copy URL https://www.pbs.org/newshour/health/why-would-a-covid-vaccine-cause-rare-blood-clots-researchers-have-found-clues Email Facebook Twitter LinkedIn Pinterest Tumblr Share on Facebook Share on Twitter Why would a COVID vaccine cause rare blood clots? Researchers have found clues Health Apr 14, 2021 6:22 PM EDT A week after receiving the AstraZeneca COVID-19 vaccine, a 37-year-old woman in Norway went to the emergency department with fever and persistent headaches. A CAT scan of her head showed a blood clot in blood vessels involved in draining the brain, but her levels of platelets, involved in clotting, were low. She was treated with platelet infusions and a blood thinner, but had a bleed in her brain the next day. She underwent surgery to relieve the pressure on her brain but died two days later. This is the side effect, known as cerebral venous sinus thrombosis, that has caused a week of worries around the COVID-19 vaccine developed by AstraZeneca.