TGA provisionally approves AstraZeneca's COVID-19 vaccine as booster dose

The third (booster) dose may be given if clinically indicated with reference to official guidance regarding the use of a heterologous third dose (e.g. mRNA vaccine). 

The decision for patients to receive Vaxzevria as a booster must be made in consultation with a medical professional. The mRNA COVID-19 vaccines (Comirnaty (Pfizer) or Spikevax (Moderna) are preferred as the booster dose in Australia, irrespective of the primary COVID-19 vaccine used. This includes for people who received the AstraZeneca COVID-19 vaccine for their primary course. 

See TGA media release here.