AstraZeneca blood clotting: what is this rare syndrome and how is it caused?

Evidence is growing of a link between the Covid-19 vaccine and a deadly thrombosis - and theories are emerging as to why

Since rare but severe clotting was seen in some people following vaccination with AstraZeneca's Covid-19 vaccine, researchers worldwide have been grappling to understand why the clotting syndrome, known as thrombosis with thrombocytopenia" (clotting with a low platelet count), occurs.

Most cases of these clots occurred in veins in the brain (a condition called cerebral venous sinus thrombosis, or CVST), though some occurred in other veins, including those to the abdomen (splanchnic vein thrombosis). It has a high death rate.