Scientists
believe they have discovered the trigger for extremely rare blood clots arising
from the Oxford-AstraZeneca coronavirus vaccine. Teams in Cardiff and the US worked
together to detail how the protein in blood is attracted to a vital
component of this vaccine. Understandably, it kicks off the chain reaction and
involves the immune system, leading to dangerous clots.

The
vaccine is made up of COVID genetic material and a weaker form of the common
cold virus. Though it is injected into the muscle, sometimes it leaks into the
bloodstream. This is where it may attract the ‘platelet factor 4’ blood
protein. Scientists have realised that in some rare cases the immune system
might confuse this platelet for the coronavirus, and then release antibodies
to attack. These antibodies clump with the platelet, leading to clots.

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AstraZeneca’s
own scientists had joined in this detective hunt, and this search has shown where
this vaccine differs from the others. Most vaccines in the UK try to deliver a
snippet of the genetic code, to train the immune system against the virus. Some
package this in spheres of fat, but AstraZeneca uses adenovirus, a common cold
virus from chimpanzees. Since researchers suspected this might be triggering
the clots, they took images with molecular-level details, using cryo-electron
microscopy.

Their
studies revealed that the outer surface of the adenovirus, which is quite
negative, attracts the platelet, which is extremely positive. Researchers have
posited that misplaced immunity is the next step, where the body starts
attacking the platelet, confusing it for the adenovirus, to which it is stuck.
This leads to antibodies being released and forming clumps, leading to
dangerous clots. However, only further research can confirm this hypothesis.

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As
things stand, these clots, called vaccine-induced immune thrombotic
thrombocytopenia, are extremely rare. They require a series of unlucky events
to form, which is perhaps why the casualties have been relatively low compared
to the number of doses administered. There have been 73 deaths out of 50 million
vaccines given in the UK. It is also thought to have saved nearly a million lives.
Nonetheless, the clots have caused concern, and alternatives are being offered
to those under 40, in the UK.

While AstraZeneca is looking to leverage these
findings to remove the side effects, some questions still remain unanswered. We
do not know whether some people are more susceptible to the clots, and why they
occur mostly in the veins of the liver and brain. Further research can answer
these questions, but the team at Cardiff has taken a step forward to improve
this adenovirus-based vaccine.