Scientists say they have discovered the 'trigger' that causes rare blood clots from the AstraZeneca vaccine.

The vaccine was administered to millions across the world, but the side-effect meant that the vaccine was no longer offered to those under 40-years-old.

However, after being given government funding to conduct research on the vaccine, scientists from Cardiff University and Arizona State University have found some answers.

Their research shows that a protein in the blood is attracted to a key component of the AstraZeneca/Oxford vaccine which causes a reaction that results in the clots.

When the vaccine is injected into the body, some of its contents can go into the blood stream.

They found that after the vaccine is administered, in some cases the body mistakes a protein for the virus (

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Dmitry Shayakhmetov / SWNS.COM)

In extremely rare cases, this can cause a protein called platelet factor 4 to be attracted to the vaccine.

When this occurs, the body mistakes the protein for the virus, and releases antibodies to fight it.

This results in a blood clot forming as the antibodies join together.

While this research has provided an understanding into the formation of the blood clots, it is not yet clear exactly why this happens.

The blood clots have been linked to 73 out of nearly 50 million doses (

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The creators of the vaccine stress that the blood clots are more likely to be caused by coronavirus infection rather than the actual vaccine.

Earlier in May, the UK's medicines safety regulator said there had been 242 clotting cases and 49 deaths after 28.5 million doses of the vaccine were given.

This caused the vaccine to not be given to under-40s.

At present, blood clots from the vaccine have been linked to 73 deaths out of nearly 50 million doses of AstraZeneca.

The vaccines that are distributed in the UK contain a party portion of the Covid-virus's genetic code which is injected into the body to train the immune system.

Some vaccines package the code inside spheres of fat, whereas AstraZeneca used an adenovirus, which in their case is a common cold that acts as a delivering agent.

The scientists suspected that this aspect of the vaccine could be linked to the blood clots.

Their research found that the outer area of the adenovirus attracts the platelet factor four protein.

Professor Alan Parker, one of the researchers at Cardiff University, said the chain reaction is an ultra-rare side-effect that occurs in a very small number of cases.

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."

Despite the very rare side effect, scientists urge the public to still get vaccinated (

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"What we have is the trigger, but there's a lot of steps that have to happen next."

Despite the very small risk of blood clots, scientists urge the public to still get vaccinated as the benefits heavily outweigh the risks.

Professor Parker added: "You could never have predicted it would have happened and the chances are vanishingly small, so we need to remember the bigger picture of the number of lives this vaccine has saved."

This groundbreaking discovery has given a better understanding into the formation of blood clots, but there is still some research to be done.

The researchers believe that the next stage may be "misplaced immunity", but this needs to be confirmed in further studies.

The findings have given a deeper understanding into the formation of blood clots, but further study needs to be done (

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Getty Images)

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."

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