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Cabramatta pharmacist Quin On runs two pharmacies,both offering walk-in AstraZeneca vaccine shots.Credit:Dean Sewell

The advice from the Australian Technical Advisory Group on Immunisation – until this week – against use of the AZ vaccine for all aged under 60 was based on benefit-to-risk analysis. ATAGI has now changed that advice for Greater Metropolitan Sydney because the risk of catching COVID-19 has risen sharply – and so too has the benefit of guarding against it with the currently most widely available vaccine,AZ.

Public confidence in AZ had been jolted by its potential - though very rare - side effect,thrombosis thrombocytopenia syndrome (TTS),causing serious illness or death. What has been missing from the public discourse is that the risk of this blood-clotting syndrome can be reduced,possibly removed. And this further tilts the benefit/risk ratio in favour of those,including myself,vaccinated with AZ.

TTS following AZ vaccination affects about one in 50,000 Australians aged over 50 and one in 35,000 below that age,with death in just 3 per cent of those cases – or less than one in a million. This tiny risk has nevertheless underpinned public policy and personal reticence.

The low death rate is due to highly effective treatment for TTS,an anticoagulant given with intravenous immunoglobulin (IVIg). It can be even further reduced by a plan to ensure TTS is diagnosed and treated at the earliest possible time.

Also missing from public discussion is knowledge that there are two simple,cheap screening tests for TTS,one or both of which could provide an early warning:the d-dimer assay (an early indicator of thrombosis) and a platelet count (thrombocytopenia means low platelet count).

The critical point is getting the tests as soon as there are symptoms. The federal government’s TTS patient information sheet lists them as:severe,persistent headache (not responding to simple analgesics),blurred vision,difficulty with speech,drowsiness,seizures,chest pain,shortness of breath,swollen leg,persistent belly pain or bleeding into the skin. So a responsibility falls on the vaccine recipient to report immediately to a doctor any of these symptoms occurring between four and 42 days after an AZ vaccination. As these symptoms occur only after serious clotting has already occurred,I would add to the list any new or unusual symptom lasting two or more days in that period.

The health system also has a responsibility here. It lies in providing clear and concise written information on the benefit of early diagnosis of TTS,on the symptoms to look out for and an agreed plan for rapid response. For those vaccinated by their GP,such a plan should be part of the discussion for informed consent. It could include the patient being given a request form for the two tests to be carried out at their discretion.

Such a plan is much more difficult to achieve for those vaccinated in pharmacies and at a mass vaccination site – as will now begin to happen in Greater Sydney. But all recipients could be provided with an information sheet with advice on what to look out for and when to contact their GP. When young people get vaccinated,mostly for the public good,there is an obligation to let them know the risk –however minuscule – and how it can ibe reduced.

For the sizeable proportion of people aged over 60 who have deferred vaccination,awaiting Pfizer,the extreme rarity of TTS needs to be stressed and their capacity to reduce the risk even further should be explained.

Well executed,this plan would carry costs and place an increased workload on GPs and the pathology system. But this is only for the three months or so before adequate supplies of other vaccines arrive.

It is a small price compared with that of the Delta wave and the cost,financial and human,of lockdowns.

Graeme Stewart is a clinical immunologist at the Westmead Institute for Medical Research and a Clinical Professor of Medicine at the University of Sydney.

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