Investigations are taking place into whether cases of a rare type of blood clot are connected to the Oxford-AstraZeneca coronavirus vaccine.
The link between the vaccine and these rare clots – known as CVSTs – is not yet proven, but experts say evidence is “firming up”.
The Joint Committee on Vaccination and Immunisation (JCVI), the group of UK experts who advise how vaccines should be used, is now recommending healthy people under 30 be offered a different vaccine.
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 (the vessels carrying blood from the heart to organs).
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 the 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