Its the first time an EU country has flexed its new export control system, brought in to try to ensure big pharmaceutical companies respect their contracts.
The move, which affects a relatively small number of the jabs, underscores a growing frustration within the bloc about the slow rollout of its vaccine drive - as well as the shortfall of promised vaccine deliveries.
The Financial Times first reported on Thursday of the ban - put in place by Italy.
An unnamed EU official has now confirmed the bloc’s executive Commission did not raise objections to the move.
Italy has been taking a tough line in dealing with vaccine shortages in the bloc, since a new government led by Mario Draghi came into power last month.
Faced with shortages of doses at the beginning of the year, the EU issued an export control system for the jabs in late January - allowing countries within the bloc to stop exports of jabs manufactured there.
Why is the EU blocking exports of the jab and how is their rollout going?
The EU has vaccinated some 8% of its population compared to more than 30% in the UK.
Australia, where the export was destined for, is still at the start of its vaccination drive.
Blocking the export puts the EU in a sticky situation - on the one hand, it is under intense pressure to ramp up the production of vaccines in the bloc, but on the other hand it wants to remain an attractive hub for pharmaceutical giants and a fair trading partner to third countries.
The EU made preparations for the rollout of vaccinations, heavily funding research and production capacity over the past year but took longer to sign off potential vaccines and subsequently sign deals with manufacturers.
The bloc has now signed deals for six different vaccines and has 450 million people to get jabbed.
Tthe EU has ordered up to 400 million doses of the AstraZeneca jab and has sealed agreements with other companies for more than two billion shots.
The bloc says that, despite the current difficulties, it is still convinced it can vaccinate 70% of the adult population by the end of summer.
It was hoped the move would force companies to respect their contractual obligations to the bloc before commercial exports could be approved.
The EU has been in dispute with AstraZeneca because it is delivering fewer doses to the bloc than it had promised.
Of the initial order for 80 million doses to the EU in the first quarter, the company will be struggling to deliver half that quantity.
There were rumours that the company was siphoning off from EU production plants to other nations - but chief executive Pascal Soriot insisted that any shortfall was to be blamed on technical production issues only.
The company refused to comment on Thursday’s news.