About the AstraZeneca COVID-19 vaccine

The AstraZeneca vaccine has been provisionally approved by the Therapeutic Goods Administration (TGA) for people 18 years and older. Find out more about the vaccine and who it is recommended for.

COVID-19 vaccination - safe, effective, free

ATAGI advice on COVID-19 AstraZeneca vaccine

The Australian Technical Advisory Group on Immunisation (ATAGI) recommends that the COVID-19 vaccine by Pfizer (Comirnaty) is preferred in adults aged under 50 years.

In people 50 years and over, ATAGI continue to advise that the benefit of vaccination with AstraZeneca COVID vaccine outweighs the risks associated with vaccination.

This recommendation is based on:

  • the increasing risk of severe outcomes from COVID-19 in older adults (and hence a higher benefit from vaccination), and
  • a potentially increased risk of thrombosis with thrombocytopenia following AstraZeneca vaccine in those under 50 years.

There appears to be a small risk of TTS in people 50 years and over, but this risk appears to be lower than in younger people. Cases overseas have been reported at all ages.

People who are considering vaccination with AstraZeneca COVID-19 vaccine should be aware of this potential complication as part of providing informed consent.

The COVID-19 AstraZeneca vaccine can be used in adults aged under 50 years where the benefits clearly outweigh the risk for that individual and the person has made an informed decision based on an understanding of the risks and benefits.

As part of Australia’s COVID-19 Vaccine and Treatment Strategy, the Australian Government has secured 53.8 million doses of the AstraZeneca vaccine, with 50 million to be manufactured onshore.

Read about the TGA’s provisional approval of the AstraZeneca vaccine.

Read the statement about the updated advice from the Department of Health Secretary and Chief Medical Officer.

Receiving the AstraZeneca vaccine

Two doses of the Astra/Zeneca vaccine are required.

From a regulatory perspective, the TGA has reviewed all the available evidence and determined that the AstraZeneca vaccine can be safely administered 4-12 weeks apart.

Drawing on the advice of the TGA and also from the implementation of the program internationally, our Australian Technical Advisory Group on Immunisation (ATAGI) has determined that to create the very best immune response, ensure the most effective clinical protection and maximise broader community coverage, the vaccine should be administered 12 weeks apart.

People who have had the first dose of the COVID-19 AstraZeneca vaccine without any serious adverse effects can be given the second dose, including adults under 50 years.

Risks of vaccination

As with any vaccine, you may have some temporary side effects after receiving a COVID-19 vaccine. Common side effects after COVID-19 Vaccine AstraZeneca include:

  • injection site pain or tenderness
  • tiredness
  • headache
  • muscle pain
  • fever and chills

Most side effects are mild and temporary, going away within 1-2 days. As with any medicine or vaccine, there may be rare and/or unknown side effects.

Thrombosis with thrombocytopenia syndrome (TTS)

The COVID-19 Vaccine AstraZeneca appears to be associated with a rare side effect called thrombosis with thrombocytopenia syndrome (TTS).

What is TTS?

TTS involves blood clots (thrombosis) and low levels of blood platelets (thrombocytopenia), In Australia symptoms of TTS have occurred between 4 and 26 days post-vaccination. The blood clots can occur in different parts of the body, such as the brain (called cerebral venous sinus thrombosis or CVST) or in the abdomen. The mechanism that causes TTS is not fully understood, but it appears similar to heparin-induced thrombocytopenia (or HIT), a rare reaction to heparin treatment.

How common is TTS?

Overall the rate of TTS is estimated to be about 6 cases per million people vaccinated. But the rate is estimated to be higher (20-40 cases per million) in those under 50 years of age. These Australian estimates are not exact because there are very small numbers of TTS cases in Australia.

What symptoms does thrombosis with thrombocytopenia syndrome usually cause?

TTS is rare and occurs around 4-26 days after vaccination. Symptoms can include abdominal pain and/or severe headache that does not settle with pain relief. People should seek medical attention immediately if they experience these symptoms:

  • a severe persistent headache with additional features
    • appears at least 4 days after vaccination
    • does not improve with simple painkillers
    • may be worse when lying down or accompanied by nausea and vomiting
  • neurological symptoms such as:
    • blurred vision
    • difficulty with speech
    • drowsiness
    • seizures
  • shortness of breath or chest pain
  • a swollen leg
  • persistent abdominal (belly) pain
  • tiny blood spots under the skin away from the site of injection together with symptoms above.

Are any groups more at risk of TTS?

No specific risk factors have been confirmed for TTS. In the countries that have reported TTS, more cases younger adults compared to older adults, and in women compared to men. However it is not yet clear if age and sex are risk factors, since the AstraZeneca vaccine was preferentially given to younger people in some countries, and since women make up a large proportion of the healthcare workers that were prioritised for vaccination. As a precaution, in Australia Comirnaty (Pfizer) vaccine is preferred for adults under 50 years of age, since their risk of TTS may be slightly higher than older people, and since they have a lower risk of severe outcomes from COVID-19 compared to older adults.

Advice for people who have had blood clots in the past

Comirnaty (Pfizer) vaccine is preferred in people who have a past history of cerebral venous sinus thrombosis or heparin-induced thrombocytopenia, given the similarities between these conditions at TTS. If you have had other types of blood clots in the past, or if you have risk factors for blood clots, you can still have the AstraZeneca vaccine. There is no evidence that people who have had a past history of other types of blood clots have an increased risk of TTS. The overall rate of blood clots has not risen in countries which have extensively used the AstraZeneca vaccine.

Advice for people who have had their first dose of AstraZeneca vaccine

Almost all (one case in the UK) of the cases of TTS reported to date have occurred after the first dose of the vaccine. People who have had their first dose without any serious side effects can be confident in getting their second dose.

Advice for people with weakened immune systems (immunocompromise)

People with immunocompromise includes those who have a medical condition or are taking medications that weaken their immune system. People with immunocompromise, including those living with HIV, have a higher risk of severe illness from COVID-19, including a higher risk of severe illness and death.

The Australian Government strongly recommends people with immunocompromise receive a COVID-19 vaccine. COVID-19 Vaccine AstraZeneca does not behave like a ‘live vaccine’. The adenovirus carrier has been modified so that it cannot replicate or spread to other cells, and it cannot cause infection. It is safe in people with immunocompromise.

Clinical trials for COVID-19 Vaccine AstraZeneca did not include people with immunocompromised but many people with such conditions have now been vaccinated worldwide. A clinical trial is being conducted of COVID-19 Vaccine AstraZeneca given to people with stable HIV infection, with results expected in a few months.

We do not know if COVID-19 Vaccine AstraZeneca is as effective in people with immunocompromise compared to the rest of the population. It is possible that it might be less effective, and so it is important to continue other preventative measures such as physical distancing after vaccination.

For more information on use of the vaccine in immunocompromised see: COVID-19 vaccination decision guide for people with immunocompromised.

Advice if you are pregnant or breastfeeding

If you are breastfeeding, it is preferable for you to have the Pfizer COVID-19 vaccine. This is the preferred vaccine in young adults. However, you can still have the COVID-19 Vaccine AstraZeneca if the benefits of vaccination outweigh the risks for you.

Read more about COVID-19 vaccines if you are pregnant or breastfeeding.

Advice for people with a history of COVID-19

If you have ever had COVID-19 in the past, tell your immunisation provider. Your provider may advise to wait for up to 6 months after recovery before having a COVID-19 vaccine. If you have ongoing illness from COVID-19, discuss the best timing of vaccination with your treating doctor. Either COVID-19 vaccine brand can be used in people with a past history of COVID-19

COVID-19 vaccine AstraZeneca and children

COVID-19 Vaccine AstraZeneca has only been provisionally approved for use in people aged 18 years or older, and cannot be given to younger people. The risk of COVID-19, especially severe disease, in children is lower than in older adolescents and adults.

Vaccine safety and reporting adverse events

The Therapeutic Goods Administration (TGA) assesses all vaccines in Australia. This ensures that in order for a vaccine to be approved it is safe, effective and manufactured to a very high quality standard. A description of the process for approval of COVID-19 vaccines is available on the TGA website. The safety of COVID-19 vaccines will be monitored continuously throughout the COVID-19 vaccination program. Suspected side effects can be reported to your vaccination provider or other healthcare professional. They will then make a formal report on your behalf to your state or territory health department or directly to the Therapeutic Goods Administration (TGA). If you would prefer to report it yourself, please visit the TGA website for information on how to report suspected side effects associated with COVID-19 vaccines.

More information

Resources for vaccination providers and their patients include:

Find out more about the provisional approval of the AstraZeneca COVID-19 vaccine.

National coronavirus and COVID-19 vaccine helpline

If you need information about COVID-19, COVID-19 vaccines or help with the COVIDSafe app, call the telephone number listed below. If you need assistance with booking a COVID-19 vaccine appointment, please note the call centre is unable to book appointments on your behalf.

View contact

Last updated: 
6 May 2021

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