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  • Mr Adrian Ling

Blood clots and the Astra Zeneca vaccine. Your questions answered.

Updated: Sep 15



There has been quite a lot of concern and questions raised by patients about the risk of a blood clot with the Astra Zeneca COVID vaccine.


Common questions are answered below.


Q: Am I at risk of a blood clot if I have the AZ Vaccine?

A: There is a very rare but serious side effect called thrombosis with thrombocytopaenia syndrome (TTS). The risk is approximately 5 in a million in those over 60, but higher in those under 60 years old.


Q: What are the risk factors for TTS? A: The main risk factor is age. People under the age of 60 are at increased risk of TTS with the AZ vaccine and therefore are advised to have the Pfizer vaccine.


Q: Why are people under the age of 60 at increased risk of TTS?

A: People under 60 have a heightened immune system. Therefore, they are more likely to have an immune reaction to the AZ vaccine.


Q: Are the causes of blood clots from the AZ vaccine similar to other blood clots?

A: No - TTS is distinct from other clotting conditions. With TTS, blood clots form because the body's immune system causes over-stimulation of platelets. Platelets are the cells that circulate in our blood and act like super glue to seal damaged areas of blood vessels.


On the contrary, blood clots that form Deep Vein Thrombosis (DVT) are due to different causes. These include one or more of the following three risk factors:

1) Vessel wall damage. This can be from physical trauma or chemical trauma (eg injection of an irritant solution into the vein), or inflammation of the vessel wall from other medical conditions.

2) Stasis or slowing of the flow of blood. Blood clots can form when blood flow slows for prolonged periods such as long aeroplane flights or prolonged bed rest.

3) An underlying medical condition that causes 'thicker' or 'stickier' blood. This is called 'thrombophilia' and can be tested for with specialised blood tests.


Q: If I have had a DVT or pulmonary embolism (PE) in the past, does this increase my risk of clots from TTS with the AZ Vaccine?

A: No. There is no evidence that the risk of TTS is increased in people who have a history of DVT or PE.


Q: If I have had a DVT or PE in the past, can I get the AZ or Pfizer vaccine?

A: Yes.


Q: If I have had a DVT or PE in the past, which vaccine is preferable?

A: Either.


Q: If I have a predisposition to form blood clots due to a thrombophilia such as Factor V Leiden or other non-immune thrombophilic disorders, can I have the AZ Vaccine?

A: Yes. This is safe, according to the joint statement from the Australian Technical Advisory Group on Immunisation (ATAGI) and the Thrombosis and Haemostasis society of Australia and New Zealand (THANZ) on Thrombosis with Thrombocytopenia Syndrome (TTS) and the use of COVID-19 Vaccine AstraZeneca.


Q: I am currently taking blood thinners - can I have the AZ or Pfizer vaccine? A: Yes. This includes people taking:




Q: Can I have the AZ vaccine if I have a history of low platelets or my current platelets are low?

A: Yes. This is safe, according to the joint statement from the Australian Technical Advisory Group on Immunisation (ATAGI) and the Thrombosis and Haemostasis society of Australia and New Zealand (THANZ) on Thrombosis with Thrombocytopenia Syndrome (TTS) and the use of COVID-19 Vaccine AstraZeneca.


Q: Where can I find out more about eligibility for COVID vaccines?

A: Your GP is an excellent port of call. In addition, the following website is useful:

https://www.health.gov.au/resources/apps-and-tools/covid-19-vaccine-eligibility-checker


Q: Where can I find out more about the AZ vaccine and risk of blood clots?

A: Your GP is an excellent port of call. In addition, the following website is useful:

https://www.health.gov.au/resources/publications/patient-information-sheet-on-astrazeneca-covid-19-vaccine-and-thrombosis-with-thrombocytopenia-syndrome-tts


Q: Should I have the COVID vaccine?

A: ABSOLUTELY YES. The risks of complications from contracting COVID far outweigh the risks of complications from having the vaccine. As Dr Norman Swan summarises:


To put things in perspective… if you catch COVID:

  • there’s around a one in three chance of long COVID

  • around a 1 in 50 chance of ending up in ICU

  • 1 in 100 chance of dying, depending on your age.

Whereas the risk of dying from the blood clotting syndrome (AstraZeneca) is one in a million or thereabouts and the heart inflammation from Pfizer about 1 in 50,000.


Q: I am a GP - where can I find out about the COVID vaccine, TTS and other related issues?

A: An excellent source is found at:

https://www.ncirs.org.au/health-professionals/covid-19-vaccines





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