COVID-19: 'Trigger' behind extremely rare AstraZeneca vaccine blood clots may have been discovered
The "trigger" behind extremely rare blood clot complications stemming from the Oxford/AstraZeneca vaccine may have been discovered, according to new research.
Scientists led by a team from Arizona State University and Cardiff University worked with AstraZeneca to investigate the causes of thrombosis with vaccine-induced immune thrombocytopenia (VITT).
TTS, which involves the formation of blood clots, is a life-threatening condition seen in a very small number of people after receiving the Oxford-AstraZeneca or Johnson & Johnson vaccines.
The scientists say they now believe they have identified how a protein in the blood is attracted to a key component of the vaccine.
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They think this kicks off a chain reaction, involving the immune system, which can culminate in dangerous clots.
The deaths of several people from blood clots caused widespread concern with the AstraZeneca vaccine and affected the way countries distribute the vaccine.
In May, the UK's medicines safety regulator said there had been 242 clotting cases and 49 deaths, with 28.5 million doses of the vaccine administered.
At the time, it was therefore decided that an alternative option would be offered to the under-40s.
Scientists and authorities have also argued that the benefits of taking the vaccine outweigh the risk.
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The study, published in the journal Science Advances, found the reaction could be traced to the way the adenovirus used by the vaccine to shuttle COVID's genetic material into cells binds with a specific protein in the blood known as platelet factor four.
Professor Alan Parker, one of the researchers at Cardiff University, said the VITT only occurs in extremely rare cases because of a chain of complex events triggering an ultra-rare side effect.
He told BBC News: "The adenovirus has an extremely negative surface, and platelet factor four is extremely positive and the two things fit together quite well."
He added: "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."
