State's huge task before lockdown eased
One figure is pointing to a much higher level of infection in Victoria than the state's daily cases suggest and it could be what holds it back from relaxing restrictions.
During a press conference on Thursday, Victoria's deputy chief health officer Allen Cheng said the state had a long way to go to get its daily case numbers to the point where stage 4 restrictions could be lifted, after reporting 240 new cases.
"Look, that's a discussion that we're having over the next week or so. It would be substantially lower than it is now," he said of daily case numbers.
"I won't give you a figure, but single digits or even low double digits."
He went on to point out the relevance of "mystery cases", also known as community transmission with an unknown source.
"It does also depend on, you know, if there are mystery cases, then we would worry more about those."
It seems Victoria's lingering number of "mystery cases" may be what holds the state back. When asked how low the number of mystery cases would have to be to ease restrictions, Prof Cheng said, "In general, a mystery case means that there's at least one other out there, so I would be happier not to have any of those."
In the past two weeks there have been 744 mystery cases identified in Victoria, with numbers ranging between 25 and 82 cases a day.
Numbers have generally trended downwards from about 70 a day, although there was a spike on Wednesday of 82 cases.
This dropped to 33 new mystery cases on Thursday.
The continuing number of mystery cases indicates Victoria still faces a tough task to get the figure to zero cases.
However, Prof Cheng stressed that the decision about when to lift restrictions was not his call.
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Premier Daniel Andrews also mentioned mystery cases and said single-figure daily case rises might not be enough to bring Victoria out of lockdown - saying the state is at risk of a "third wave".
He said loosening restrictions was "not just about the raw number of new cases".
"It will be some of the circumstances that sit behind those," Mr Andrews said.
"If you had very low numbers of community transmission or mystery cases, and you had 20 cases, but they were all linked to known and contained outbreaks, then that is, in fact, in some respects, a lower number than it might seem."
Experts have previously told news.com.au that Victoria won't be able to ease stage 4 restrictions within six weeks if it aims to get mystery cases down to zero.
"If the goal is no community transmission, our modelling is telling us that six weeks is not enough," Economist and modeller Professor Quentin Grafton of Australian National University said.
"We would suggest that at least eight weeks would be required, but the additional two weeks does have a large pay-off."
Prof Grafton believes stage 4 restrictions shouldn't be eased until the state records at least some days of zero cases.
"What we've seen in Victoria and around the world is that as long as we have community transmission, there is a real likelihood that COVID will come back," he said.
"If we get to no community transmission then less social distancing will be required over the next 12 months."
Melbourne University epidemiologist Professor Tony Blakely agrees that six weeks probably won't be enough if the state is aiming to eliminate community transmission.
"At this rate of progress we'll be lucky if we are at less than 50 cases a day by the end of the six-week lockdown," he told news.com.au.
If Melbourne did go to Stage 3 restrictions, this would also be unlikely to keep driving down the case numbers.
"We've already tried that, stage 3 was implemented in Melbourne and it didn't work," Prof Grafton said.
Originally published as Vic's huge task before lockdown eased