Scientists believe they have discovered why the Oxford/AstraZeneca Covid-19 vaccine may cause blood clots in a very small number of people.
A team of researchers from Cardiff and the US found that a protein in the blood is attracted to a key component of the vaccine, the BBC reported. This, they suggest, causes a chain reaction in the immune system that can culminate in dangerous clots.
Professor Alan Parker, one of the researchers at Cardiff University, said the side effect occurs only in extremely rare cases because of a chain of complex events in those individuals.
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His team found that the outer surface of the adenovirus used by AstraZeneca attracts the platelet factor four protein to it like a magnet.
Parker said: “The adenovirus has an extremely negative surface, and platelet factor four is extremely positive and the two things fit together quite well.”
He added that his team has been able to prove the link between the “key smoking guns of adenoviruses and platelet factor four”.
The scientists believe that the next stage of the process is “misplaced immunity”, but this needs to be confirmed in further research.
Sky News noted that the number of people affected is thought to be very small. 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.
Nevertheless, concerns over rare blood clots have influenced how the vaccine has been deployed around the world. For example, the AstraZeneca jab was not offered to the under-40s in the UK and alternatives were used instead.
AstraZeneca claimed that clots were more likely to occur because of a Covid infection than the vaccine, and insisted that the complete explanation for why they occur had not yet been established.
Commenting on the findings, a spokeswoman for the company said the research is “not definitive” but “offers interesting insights”.
AstraZeneca added that the vaccine is thought to have saved more than a million lives around the world and prevented 50 million cases of Covid. The University of Oxford, which worked on the vaccine, declined to comment on the research.
