A Southampton stroke specialist is part of a national team of experts studying blood clots in the brain following Covid-19 vaccination with a focus on potential treatments.

Dr Richard Marigold, consultant stroke physician at University Hospital Southampton (UHS), collaborated with experts across the UK in a study published in The Lancet last week.

This follows the emergence earlier this year of vaccine-induced immune thrombotic thrombocytopenia (VITT), a condition which is a very rare consequence of Covid-19 vaccination.

VITT is characterised by a blockage of the veins and a marked reduction of platelets – tiny cells in the blood that form clots to stop or prevent bleeding.

This can lead to abnormal blood clot formation, swelling and haemorrhage (bleeding) in the brain.

The condition occurs more commonly in women under the age of 50 years who present within five to 24 days of vaccination with blood clots in unusual sites. The majority develop in the brain and are associated with a condition called cerebral venous sinus thrombosis (CVST).

This can lead to a build-up of pressure and the potential need for surgery and is associated with a 4% mortality of patients during their hospital admission.

Currently, the treatment combines blood thinning medication and intravenous immunoglobulin – a blood-based medication delivered by an injection into the vein that contains antibodies to fight inflammation and counteract abnormal immune reactions.

Dr Marigold said: “This is an important observational study about vaccine induced immune thrombotic thrombocytopenia leading to blood clots forming within the cerebral veins following COVID-19 vaccination.

“It supports this rare condition being treated with non-heparin blood thinning medication and intravenous immunoglobulin, reducing mortality and increasing the chances of patients returning home to independent living.

“However, we would urge caution in interpreting this observational data as it is not a randomised controlled trial, and more studies are needed to establish how effective the medications are.”

Although VITT-associated CVST is a severe condition, it appears to be extremely rare and the authors stress that, for the vast majority of people, the risk to their health of not getting vaccinated against COVID-19 is likely to be much higher.