What started with just four coronavirus cases in Melbourne a few days ago has now more than doubled, as close contacts are tracked down, isolated and tested.

While cases are being linked to each other, how they relate back to a hotel quarantine breach in South Australia is still unclear.

The other big challenge facing health authorities will be making sure every case is tracked down, but that's a job that gets harder with every new positive case.

So on today's Coronacast, what are we hoping for in the days ahead?

Also on today's show:

• The TGA allows more flexibility for storing Pfizer vaccine

• What information is there on how the vaccine works for people with blood disorders?

• A few of your vaccination stories