National researchers have determined the case definition criteria for the diagnosis of patients with vaccine-induced immune thrombocytopenia and thrombosis (VITT), a new thrombotic syndrome associated with the ChAdOx1 nCoV-19 vaccination.
The paper, published in the New England Journal of Medicine, looks at symptoms, signs and outcomes of the first 220 UK cases of VITT.
The research team, led by Dr Sue Pavord of Oxford University Hospitals (OUH) NHS Foundation Trust, found that the overall mortality rate of those presenting to hospitals with definite or probable VITT was just over 22%.
The chances of death increased significantly the lower the platelet count and the greater the activation of the blood clotting system, increasing to 73% in patients with a very low platelet count and intracranial haemorrhage following blood clots in the brain (cerebral venous sinus thrombosis – CVST).
Dr Pavord, a Consultant Haematologist at OUH, said: “It’s important to stress that this kind of reaction to the Oxford-AstraZeneca vaccine is very rare. In those aged under 50, incidence is around one in 50,000 people who have received the vaccine. But our study shows that for those who develop VITT, it can be devastating: it often affects young, otherwise healthy vaccine recipients and has high mortality. It is particularly dangerous when the patient has a low platelet count and bleeding in the brain.
“VITT is a very new syndrome, and we are still working out what the most effective treatment is, but identifying prognostic markers has helped to determine what is the more effective way to manage the condition. For example, we have adapted our treatments for patients with the most severe disease, to include plasma exchange with some success.”
Dr Pavord added: “We have worked relentlessly to understand and manage this new condition, so that the hugely successful vaccine roll out can continue, which is the most viable solution to the global pandemic.”
The Expert Haematology Panel, comprising Drs Sue Pavord, Beverley Hunt, Marie Scully, Will Lester and Mike Makris, and Catherine Bagot (Scotland), conducted daily meetings during this period to support UK haematologists with patient diagnosis and management.
Some 85% of the patients studied were under the age of 60, despite most of the elderly population having been vaccinated. Almost all of those presenting to hospital experienced the condition between five and 30 days after their first vaccination with ChAdOx1 nCov-19.
There was no difference in incidence between the sexes, and no prior medical condition was seen more often than expected for the general population.
OUH has increased clinic capacity to provide dedicated medical care for patients with VITT, to ensure long-term monitoring and support for these patients and others who develop low platelets after Covid-19 vaccination.