11 August 2021

Researchers present first findings on blood clotting with low platelets after COVID-19 vaccination

A national team of researchers have defined criteria for the diagnosis of patients with blood clotting associated with the Oxford Astrazeneca Covid vaccination.

Person receiving vaccine
  • New research has determined the case definition criteria for the diagnosis of patients with blood clotting associated with the Oxford Astrazeneca Covid-19 vaccine 
  • The study looked at the symptoms, signs and outcomes of the first 220 UK cases of vaccine-induced immune thrombocytopenia and thrombosis (VITT)
  • The findings show that the overall mortality rate of those with definite or probable VITT was 23 per cent

A national team of researchers have defined criteria for the diagnosis of patients with blood clotting associated with the Oxford Astrazeneca Covid vaccination.

The paper, published in the New England Journal of Medicine, looks at symptoms, signs and outcomes of the first 220 UK cases of vaccine-induced immune thrombocytopenia and thrombosis (VITT), a new thrombotic syndrome. 

The research found that the overall mortality rate of those presenting to hospitals with definite or probable VITT was 23 per cent. The chances of death increased significantly the lower the platelet count and the greater the activation of the blood clotting system, increasing to 73 per cent in patients with a very low platelet count and intracranial haemorrhage following blood clots in the brain. 

Some 85 per cent 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.

Professor Mike Makris, co-author of the research from the University of Sheffield, said: “This was a new serious disease that appeared for the first time in March 2021 and followed vaccination with the Oxford AstraZeneca vaccine. Its management was particularly challenging because some patients presented with severe thrombosis and bleeding at the same time.

“We were relieved to observe that following the introduction of the age restrictions for vaccination with the Oxford AstraZeneca vaccine, we were no longer seeing new VITT cases. This has been almost entirely an issue associated with the first dose of this vaccine."

It is important that we all get vaccinated against COVID-19 because the risks from the virus are much higher than the risks from the vaccine.

Professor Mike Makris 

Professor of Haemostasis & Thrombosis

Dr Sue Pavord of Oxford University Hospitals (OUH) NHS Foundation Trust, who led the research, 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 EHP, 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.


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