The Federal Government has revealed that it has sourced another 10 million doses of the Pfizer vaccine, bringing the total ordered for Australia to 150 million.

Most Australians will still be given the Oxford AstraZeneca vaccine if it is approved by the regulator.

Also, it's been announced that everyone in Australia, including all visa holders, will be given a vaccine for free and it's hoped the rollout will be completed by October.

So on today's Coronacast, why have we ordered so many vaccines? And what do we hope the vaccination program will achieve?

Also on today's show:

* Do we know if vaccines prevent transmission yet?

* What's the latest from the WA and Victorian outbreaks?

* What medical conditions could prevent or limit COVID vaccination?

* What is the difference between the SA variant, the UK variant and the Brazil variant? Are they the same thing?