AZ clots ‘more aggressive, lethal but also rare’

Major study finds blood clots caused by AstraZeneca are more deadly than any other thrombosis conditions, with up to 23pc of victims dying.

The very rare blood clots that can be caused by the Oxford-AstraZeneca coronavirus vaccine are more aggressive and deadly than other thrombosis conditions, leading scientists say.

The first study of its kind has examined vaccine-induced immune thrombocytopenia and thrombosis (Vitt), which researchers said affected about one in 50,000 recipients under 50.

Of the 220 confirmed cases analysed, 23 per cent died within weeks of vaccination. All the cases studied were people who had been given the Oxford-AstraZeneca or Johnson & Johnson vaccines, which use a different technology from that of the Pfizer-BioNTech or Moderna vaccines. The average age was 48.

The scientists found that 73 per cent of patients who had a very low platelet count and bleeding in the brain after the blood clots did not survive.

A research team led by Dr Sue Pavord, of Oxford University Hospitals NHS Foundation Trust, was quickly assembled in March when it became clear that vaccine-related blood clotting in young patients was a new syndrome. In April the Joint Committee on Immunisation and Vaccination advised that adults under 30 should be offered an alternative vaccine. The following month this was amended to adults under 40.

Pavord 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.”

The team found that anyone could develop Vitt. There are no predetermining factors and the cause is unknown. On average clots developed 14 days after vaccination, the study found.

Thrombocytopenia is a condition when someone has a low count of platelets, the cells that help the blood to clot. Thrombosis occurs when clots block veins or arteries and can lead to strokes or heart attacks.

“This condition, Vitt, seemed more aggressive than what we were familiar with,” Pavord said. “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.”

The team has set out guidance for clinicians that can help to diagnose Vitt. Treatments such as plasma exchange, which involves removing and replacing the fluid in the blood, can dramatically raise survival chances for those with severe disease.

The experts dismissed comparisons with the risk of clotting from the contraceptive pill because the vaccine could cause “very tricky and quite profound levels of thrombosis” with alarming death rates.

Up to July 28 the Medicines and Healthcare Products Regulatory Agency (MHRA) had received reports of 411 cases of significant blood clots together with low platelet counts in the UK after the vaccine was administered. The overall case fatality rate was 18 per cent, with 73 deaths, six of which occurred after the second dose, the MHRA said. At that time, the estimated number of first doses of Oxford-AstraZeneca vaccine administered in the UK was 24.8 million and the estimated number of second doses was 23.6 million.

Pavord said that the team had not seen any new cases of Vitt in the past three to four weeks, suggesting that the decision to offer an alternative vaccine to under-40s may have played a role.

Pavord said: “We haven’t seen new cases for the last four weeks or so and cases of Vitt have plummeted since the initial surge in March and April before the age limitations of AZ were introduced. However, they could rise again if people who have been double-dosed with Pfizer received an AZ booster in the autumn.”

The team are examining whether there are genetic factors that increase the risk of Vitt.

The study is published in The New England Journal of Medicine. One of its authors, Michael Makris, professor of haemostasis and thrombosis at University of Sheffield, said that despite the findings the team were all “strong pro-vaccination advocates”. Makris, who was vaccinated using AstraZeneca, said: “I believe the whole world should be vaccinated against Covid-19. We are not here to say anything bad about AstraZeneca, it is a matter of targeting it.”

The Times