Why Would a Covid Vaccine Cause Rare Blood Clots? Researchers Have Found Clues

April 13, 2021

(STAT News) – Most tellingly, both the paper from Norway and the second paper, which looked at patients from Austria and Germany, found that blood clots were seen in people who had high levels of antibodies to platelet factor 4, the same types of antibodies reported, infrequently, after treatment with heparin. That doesn’t explain why a vaccine is causing the immune system to produce those antibodies, or whether other vaccines might do the same. But it provides a first step toward explaining the side effect, which experts say is extremely rare, and to looking into whether the same types of rare clots could occur with other shots.