Covid: Scientists Discover Rare Clot Trigger After AstraZeneca Vaccine

Covid: Scientists Discover Rare Clot Trigger After AstraZeneca Vaccine

Scientists believe they have found “the trigger” that can lead to extremely rare blood clots after Oxford-AstraZeneca’s Covid-19 vaccine.

The team, based in Cardiff and the United States, showed in detail how a protein in the blood is attracted to a key component of the vaccine.

They believe this sets off a chain reaction involving the immune system that can lead to dangerous clots.

The vaccine is believed to have saved about a million lives during the Covid pandemic.

However, concerns about rare blood clots have shaped the way the vaccine has been used around the world – in the UK, for example, an alternative has been offered for those under 40.

The problem also started a scientific hunt to find out what was going on and whether it could be avoided. Cardiff’s team received emergency government funding to find the answers.

AstraZeneca’s own scientists also joined the research project after previous results of the team’s work were published.

An AstraZeneca spokeswoman emphasized that clots are more likely to occur because of a Covid infection than because of the vaccine, and that the full explanation of why they occur has not yet been established.

“While the research is not definitive, it offers interesting insights and AstraZeneca is exploring ways to build on these findings as part of our efforts to remove this extremely rare side effect,” he added.

There were two initial clues to researchers investigating rare blood clots:

  • The greatest risk of clots was seen with only some of the vaccine technologies
  • People with clots had unusual antibodies that attacked a protein in their blood called platelet factor 4

Several vaccines attempt to deliver a fragment of the Covid virus genetic code to the body to train the immune system. Some package this code inside fatty spheres, while AstraZeneca uses an adenovirus (specifically a chimpanzee common cold virus) as its microscopic messenger.

The researchers thought the adenovirus could be linked to rare clots that occur in some people. So they used a technique called cryoelectron microscopy to image the adenovirus in detail at the molecular level.

The study, published in Science Advances, reveals that the outer surface of the adenovirus attracts platelet factor 4 protein like a magnet.

Professor Alan Parker, one of the Cardiff University researchers, told BBC News: “Adenovirus has an extremely negative surface, and platelet factor 4 is extremely positive and the two things fit together very well.”

He added: “We have been able to prove the link between the main weapons of adenoviruses and platelet factor 4. What we have is the trigger, but there are a number of steps that need to happen next.”

Researchers think the next stage is “lost immunity”, but this needs to be confirmed in future research.

It is believed that the body begins attacking platelet factor 4 after mistaking it for part of the foreign adenovirus to which it is attached. Thus, antibodies are released into the blood, which aggregate to platelet factor four and trigger the formation of dangerous blood clots. However, this requires a series of unfortunate events, which could explain why clots are so rare.

These clots, known as vaccine-induced immune thrombotic thrombocytopenia, have been associated with 73 deaths in nearly 50 million doses of AstraZeneca given in the UK.

“You could never have predicted that this would have happened and the chances are very slim, so we need to remember the big picture of the number of lives this vaccine has saved,” Parker said.

AstraZeneca said estimates suggest the vaccine saved more than a million lives worldwide and prevented 50 million cases of Covid.

Oxford University did not comment on the research.

Will Lester, a consultant hematologist at the University Hospitals Birmingham NHS Trust, praised the “very detailed” research, saying it helps explain the “most likely initial step” in clotting.

He added: “Many questions still remain unanswered, including whether some people might be more susceptible than others and why thrombosis (clotting) is more commonly in the brain and liver veins, but this may come with time and research. future”.

The Cardiff team hopes their findings can be used to improve adenovirus-based vaccines in the future to reduce the risk of these rare events.


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