Scientists believe ‘trigger’ for rare blood clots after AZ vaccine found

Scientists believe they may have found the “trigger” behind the rare blood clot complications stemming from the AstraZeneca Covid-19 vaccine.

According to an international team of researchers from Cardiff and the US, the reaction can be traced to the way the adenovirus used in the vaccine to shuttle the coronavirus’ genetic material into cells binds with a specific protein in the blood, known as platelet factor 4 (PF4).

Researchers think this may spark a chain reaction in the immune system which can culminate in the development of blood clots — a condition known as vaccine-induced immune thrombotic thrombocytopenia (VITT).

Concerns about rare blood clots had an impact on how the company’s vaccine was used around the world, with alternatives offered to people aged under-40 in some countries. AstraZeneca maintained that clots were much more likely to occur because of a Covid-19 infection than the vaccine.

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Prof Alan Parker, from Cardiff University’s School of Medicine, said: “VITT only happens in extremely rare cases because a chain of complex events needs to take place to trigger this ultra-rare side effect.

“Our data confirms PF4 can bind to adenoviruses, an important step in unravelling the mechanism underlying VITT. Establishing a mechanism could help to prevent and treat this disorder.

“We hope our findings can be used to better understand the rare side effects of these new vaccines — and potentially to design new and improved vaccines to turn the tide on this global pandemic,” he added. – PA