The AstraZeneca vaccine is associated with a rare risk of a condition called thrombosis with thrombocytopenia syndrome, or TTS.

TTS involves blood clots (thrombosis) along with low platelet levels (thrombocytopenia), and may occur between 4 to 28 days after vaccination. It is currently estimated to affect around 6 people per 1 million doses. To date, almost all reported cases were after the first dose of the vaccine. Use the COVID-19 vaccine side effects symptom checker if you have concerns about any symptoms after your vaccine. The checker is also available through the National Coronavirus Helpline, 1800 020 080, 24 hours a day

Younger adults under 60 years of age appear to have a higher risk of TTS than older adults. For this reason, the AstraZeneca vaccine is no longer recommended for people under60 years old in Australia.1

People under 60 may still choose to have the AstraZeneca vaccine if, after talking to their doctor, they decide the benefits outweigh the risks. This Department of Health factsheet may help you decide.People under 60 who have had a first dose of AstraZeneca vaccine, are advised to still have the second dose as the potential risks of TTS are far lower than with the first dose. 

The Pfizer vaccine is not associated with a risk of TTS.1


  1. (2021, May 10). COVID-19 vaccines: Frequently asked questions. Retrieved from NCIRS:
  2. Department of Health. (2021, May 7). Weighing up the potential benefits against risk of harm from COVID-19 Vaccine AstraZeneca. Retrieved from Australian Government Department of Health:

Updated 14 July 2021