Scientists may have solved an important part of the mystery of ultra-rare blood clots linked to adenovirus COVID-19 vaccines

Alan Parker, author on the study, from Cardiff University's School of Medicine - An international team of scientists believe they may have found a molecular mechanism behind the extremely rare blood clots linked to adenovirus COVID-19 vaccines. Scientists from Cardiff University and Arizona State University worked with AstraZeneca to investigate vaccine-induced immune thrombotic thrombocytopenia (VITT), also known as thrombosis with thrombocytopenia syndrome (TTS), a life-threatening condition seen in a very small number of people after receiving the Oxford-AstraZeneca or Johnson & Johnson vaccines. The global team used state-of-the-art technology to analyse the AstraZeneca vaccine in minute detail to understand whether the ultra-rare side effect could be linked to the viral vector. Their findings suggest it is the viral vector - in this case an adenovirus used to shuttle the coronavirus' genetic material into cells - and the way it binds to platelet factor 4 (PF4) once injected that could be the potential mechanism. In very rare cases, the scientists suggest, the viral vector may enter the bloodstream and bind to PF4, where the immune system then views this complex as foreign. They believe this misplaced immunity could result in the release of antibodies against PF4, which bind to and activate platelets, causing them to cluster together and triggering blood clots in a very small number of people after the vaccine is administered. Their findings are published today in the international journal Science Advances.