Southampton stroke specialist contributes to national study into rare post-vaccination blood clots

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.

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).

CVST occurs when blood clots form in the veins in the brain and can produce swelling and bleeding that sometimes prevents blood from draining properly.

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.

Patients observed in this study with VITT-associated CVST had a mortality rate which was around seven times higher, at 29%, compared with CVST alone.

This poorer outcome is partly explained by the abnormal blockage of veins being much more extensive in VITT, with more veins blocked both in the head and other areas in the body.

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.”

He added: “Further research is required to explain the underlying mechanisms causing this reaction to prevent it happening and improve future vaccine design.

“In addition, clinicians need to be aware of the early markers of this condition, as without recognition and prompt treatment, the outcome can be poor.”

Dr Richard Perry, lead author and Consultant Neurologist at the National Hospital for Neurology and Neurosurgery at University College Hospital London said: “With an illness of such severity, often in young patients who were previously fit and well, doctors have been desperate for evidence regarding treatments that might prevent some of the death and disability that arises from this condition.

“While an observational study is not the ideal platform to provide evidence for which medications work, it may be a long time before we have evidence from randomised clinical trials, the gold standard for testing new treatments.

He added: “For the moment we are dependent on observational studies like CAIAC for our evidence.”

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.