‘We can treat it’: Mortality rate of rare condition linked to AstraZeneca shot plunges

Doctors are now confident they can detect and treat the rare blood clotting syndrome associated with AstraZeneca’s vaccine, with just one death recorded so far.

When the syndrome, known as thrombosis with thrombocytopenia (TTS), was first identified one in four people with it died.

Professor Huyen Tran is leading the care for people who have suffered blood clots after having a dose of AstraZeneca’s vaccine.Credit: Eddie Jim

But the fatality rate has been dropping in Europe, where it was first identified. As of last Thursday, Australia had recorded 31 confirmed and 10 probable cases.

Of those cases, 23 are out of hospital and recovering, four require ongoing care and 13 remain in hospital.

Two trends are emerging, experts say: doctors are detecting more cases due to better screening, which shows the syndrome is more common but less deadly than first thought, and treatments have improved dramatically.

“We can recognise it, we can diagnose it, and we can treat it,” said Huyen Tran, head of the Alfred hospital’s thrombosis and haemostasis unit and a member of the Thrombosis and Haemostasis Society of Australia and New Zealand’s working group investigating the syndrome

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Professor Tran has been personally involved in the care of nearly every patient with TTS in Victoria.

He said it was always going to be the case that newly discovered conditions had higher mortality rates at first, but that the true mortality rate would end up being much lower.

The syndrome is extremely unusual, doctors say, as it causes both blood clots and low levels of platelets in the bloodstream.

Staff at a mass vaccination centre at the Melbourne Exhibition Centre.Credit: Getty

Australia’s Technical Advisory Group on Immunisation (ATAGI) advised in April that Pfizer’s vaccine should be “preferred” for people under 50 due to evidence the risk of the syndrome was higher for younger people.

At the time, the advisory group estimated it occurred at a rate of between four and six cases per million, with a fatality rate of 25 per cent (meaning one in four people with the syndrome were expected to die), based on overseas data.

Europe has now doubled its estimates to around 20 cases per million doses for those under 50; for over 50s, the rate is closer to 10 in a million.

Australia’s fatality rate - the percentage of people who die after developing a clot - presently sits between 2.4 and 3.2 per cent. However, Australia has done fewer vaccinations than other countries and has not been giving AstraZeneca to people under 50.

Britain’s fatality rate sits at 18 per cent.

“When you look at the data from overseas, that mortality rate is coming down – most are coming down to 10 per cent, and I presume it will come down further again,” said Paul Monagle, a professor at the University of Melbourne where he is studying the syndrome.

“It’s not the uniformly catastrophic disease that was originally presented.”

To treat the rare syndrome, Australian doctors are using injections of antibodies taken from the blood of donors. This treatment, known as intravenous immunoglobulin, has been shown to be effective in similar autoimmune blood clotting disorders.

Christopher Frith, of the Binjari community, receives his first dose of the AstraZeneca vaccine.Credit: Rhett Wyman

ATAGI’s decision to prefer Pfizer over AstraZeneca for people under 50 was made after balancing risk – including the 25 per cent fatality rate – and reward.

Experts said a lower fatality rate and Melbourne’s current COVID-19 outbreak did change that risk-benefit calculation, but not enough to alter the earlier recommendation.

“Even if mortality drops, as is likely, it does appear to be a more severe disease in the younger population with worse non-fatal disease course and outcomes than in the over 50s,” said Professor Jim Buttery, head of epidemiology at the Victorian immunisation safety service.

ATAGI declined to comment directly on whether the risk-benefit calculus was changing.

It remains unclear just what causes the syndrome.

Early attention focused on the possibility AstraZeneca’s vaccine was causing the immune system to make an antibody against a protein released by blood platelets. The antibody then binds to the platelets, activating them and causing blood clots to form.

Late last month German scientists uploaded a paper – not yet peer reviewed – suggesting AstraZeneca’s vaccine may cause immunised cells to release proteins in the blood, which are then bound by antibodies, causing blood clots.

“There is a lot more work to be done yet before we get to the bottom of it,” said Professor Monagle.