HRI investigates link between AstraZeneca Covid vaccine and blood clots

In an Australian first, a pilot study will seek to find biomarkers for blood clot risks in patients who have been given the AstraZeneca COVID-19 vaccine.

A team of scientists from the Heart Research Institute (HRI) will screen patients 10 days after their first injection to determine their risk of developing a rare blood clot from the vaccine.

Dr Freda Passam, Group Leader of the Haematology Research Group at HRI/Charles Perkins Centre of The University of Sydney, is spearheading the pilot study and says it will help understand why some people are more susceptible to blood clotting than others.

“While the risk of a blood clot is rare from the AstraZeneca vaccine, we know if it happens, it will occur between five and 30 days after the first injection,” Dr Passam says.

“Currently the only warning signs a blood clot may form are a headache or bad stomach pains within a month of the vaccine being administered. This research will alert us to the risk of clotting earlier and answer why it happens in some and not others.”

Bede Johnston, one of the scientists in the Haematology Research Group, explains, “We developed an assay – an investigative procedure – that simulates blood circulation where we intend to test the effect of the vaccine on a fake blood vessel.

Bede Johnston holding biochip

Bede Johnston holding a biochip used in this study

“This will enable us to see if there is too much inflammation in the blood circulation, which could allow people to take preventative action in the form of an anti-inflammatory to ensure a blood clot doesn’t form.

“We have previously used the assay to study the blood from healthy individuals and patients with other clotting tendencies. This new study will involve 50 individuals receiving the AZ vaccine.”

The blood sample would be taken by Sydney’s Royal Prince Alfred (RPA) Hospital and sent to HRI researchers through a laboratory.

Haematology HRI is working with Dr Paul Coleman from Centenary Institute and Dr Vivien Chen from ANZAC Institute to produce and test the devices needed for the assays.

How you can help

HRI urgently needs around $300,000 for more dedicated researchers to work around the clock to run the experiments, coordinate with the RPA and analyse data. Donations to accelerate this research can be made at

Header image: Dr Freda Passam, Haematology Research Group Leader at HRI

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