No cases of vaccine-induced clotting reported in last month, experts say

Some 170 patients in the UK have been diagnosed with vaccine-induced immune thrombocytopenia and thrombosis since mid-March

Under-40s have been offered alternatives to the AstraZeneca jab since May (Getty)

No confirmed cases of vaccine-induced clotting have been reported in the UK in the last four weeks, leading experts have said.

Early fears over the condition, an exceptionally rare reaction to the Oxford-AstraZeneca vaccine, sparked reluctance across the world to administer and accept the jab, with many governments choosing to limit its use to elderly adults.

New research has found that 170 patients in the UK have been diagnosed with vaccine-induced immune thrombocytopenia and thrombosis (VITT) since mid-March. But as use of the AstraZeneca jab has slowed in Britain, with those under 40 receiving Pfizer instead, no new cases of VITT have been reported in the past month.

The scientists behind the study, which presents five key signs for recognising and diagnosing VITT, all advocated for the continued use of the jab. They said their findings would help to better treat the small number of people who fall ill from the condition.

Dr Sue Pavord, a consultant haematologist at Oxford University Hospitals Foundation Trust who led the research, said “identifying prognostic markers has helped to determine what is the more effective way to manage the condition”.

VITT typically involves clotting within one of the key veins that drain the brain, which can lead to stroke, combined with a dangerously low blood platelet count. However, clots can also form in the lungs, leg and even stomach.

The condition affects around one in 50,000 people aged under 50 who have received the AstraZeneca vaccine and causes death in an estimated 22 per cent of affected patients, the research showed. The odds of death increased almost threefold in patients who suffered from clotting within the brain.

The study, published in the New England Journal of Medicine, examined 294 patients with suspected VITT who were taken to hospital between 22 March and 6 June. A total of 170 were found to be definite cases, while 50 were judged to be “probable”.

The researchers used five key criteria to confirm VITT in these people, including the onset of symptoms five to 30 days after vaccination and the presence of an antibody specific to a platelet called factor 4.

The patients had a median age of 48, while 85 per cent of those evaluated were under the age of 60. There was no difference in incidence between men and women, and no underlying health conditions or genetic factors were linked to those who fell ill with VITT.

“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,” said Dr Pavord. “It is particularly dangerous when the patient has a low platelet count and bleeding in the brain.”

The progress made in defining VITT has allowed doctors to adapt treatment for patients with the most severe symptoms, she said. And plasma exchanges have had “some success”.

Other treatments can involve administering antibodies intravenously to increase platelet count, steroids to dampen the immune system and blood thinners to prevent further blood clots.

The use of the AstraZeneca vaccine in under-40s was stopped in Britain at the beginning of May. The Pfizer jab, which has not been linked to VITT, was offered to this age group instead.

As the national rollout has worked its way down to 16-year-olds, few first AstraZeneca doses have been administered since. As a result, said Dr Pavord, “we haven’t seen new cases for the last four weeks or so”.

“What we have learned in the UK is also hugely important to other countries, because if they can recognise this condition early, manage it promptly and manage it well, then it allows the vaccine rollout to continue in their countries,” she said.

“That’s hugely important. It’s the only way we’re going to tackle this global pandemic.”

Dr Pavord’s team of experts have been meeting daily since the middle of March, when health authorities first became aware of VITT, to identify cases and better understand the condition.

Data from the Medicines and Healthcare products Regulatory Agency (MHRA) presents a slightly different picture for VITT incidence. Out of 24.8 million first doses of the AstraZeneca vaccine, there were 411 reported cases up to 28 July, the MHRA reports.

However, Michael Makris, a professor of haemostasis and thrombosis at the University of Sheffield involved in the research, said the regulator defined cases differently and were possibly reporting too high a number.

“The MHRA collects reports from any clinician, not just haematologists,” he said. “What they are reporting in patients with low platelets and thrombosis, it doesn’t have to be in the timescale [of five to 30 days after vaccination], it doesn’t have to have anti-platelet factor 4.

“We have a very strict definition, and they’re collecting a whole group. I’m hoping they go back at some stage and use our definition to define how many of their cases are true VITT.”