A team of scientists from Cardiff University have worked alongside Arizona State University and AstraZeneca to understand why the vaccine is causing blood clots in some of those who have had the jab.
A small number of people have developed Thrombosis with vaccine-induced immune thrombocytopenia (VITT) after receiving the vaccine which causes the formation of blood clots. The life- threatening condition has also formed in a number of those who have received the Johnson & Johnson vaccine.
Scientists have discovered that a protein found in blood, is attracted to a key component within the vaccines. They believe that this starts a chain reaction with the immune system causing the blood clots to form.
The UK’s medicines safety regulator has revealed that there has been 242 clot cases and 49 deaths since May.
The cases meant that the AstraZeneca vaccine was not offered to anyone under the age of 40 despite 28.5 million doses already being administered to those over forty.
Professor Alan Parker, a researcher at Cardiff University said: "The adenovirus has an extremely negative surface, and platelet factor four is extremely positive and the two things fit together quite well.
“We've been able to prove the link between the key smoking guns of adenoviruses and platelet factor four.
"What we have is the trigger, but there's a lot of steps that have to happen next."
Dr Will Lester, a consultant haematologist, said: "This is a very detailed scientific study from experts in the field and provides further pieces to a jigsaw of understanding vaccine induced thrombocytopenia and thrombosis.
"The authors reasonably speculate that one might be able to modify future adenoviral based vaccines to avoid this unwanted rare untoward effect.
"Many questions still remain unanswered; including whether some people may be more susceptible than others and why the thrombosis is most commonly in the veins of the brain and liver, but this may come with time and further research."