Rare blood clots - what you need to know

Posted: April 19th 2021


This is a very illuminating article providing some fascinating and emerging insights – it tells us:

Investigations are taking place into whether cases of a rare type of blood clot are connected to both the Oxford-AstraZeneca and the Johnson and Johnson (J&J) coronavirus vaccines.

The link between the AstraZeneca vaccine and these rare clots - known as CVSTs - is not yet proven, but UK experts say evidence is "firming up".

The Joint Committee on Vaccination and Immunisation (JCVI), which advises how vaccines should be used, is recommending healthy people under 30 be offered a different vaccine.

The Johnson and Johnson jab is not yet available in the UK - although 30 million doses are on pre-order.

However, the rollout in the US, South Africa and European Union is temporarily on hold.

What are CVST clots?

CVST stands for cerebral venous sinus thrombosis. Put simply, this is a clot found in a large vein in the brain.

Blood normally travels through veins from the brain back to the heart.

The CVST clot can block the flow of blood in the brain, reducing oxygen supply and potentially causing damage - stopping the central nervous system from working properly.

Rare clots have also been found in other areas, such as the large veins in the abdomen, in people who have had the Oxford-AstraZeneca jab, and, in a handful of cases, in some arteries (blood vessels carrying blood from the heart to organs).

Why do the clots happen? 

No-one is yet sure, but there are certain factors in common.

In the CVST cases under investigation, the patients were all found to have low numbers of platelets - these are blood cells that normally help repair bleeding in the body. 

Patients were also found to have a particular antibody (an immune protein that often helps fight against infection) in their blood that activates platelets. 

The antibody causes the platelets to mistakenly clump together and form clots, and in turn activates other parts of the body's clotting system. 

A combination of clots and low platelets is one of the features doctors are now looking out for. 

Scientists think the immune system is essentially misfiring in this situation but there is a lot more that needs to be understood.