Explainer: Is Victoria's second wave of coronavirus cases over?

Victoria Premier Daniel Andrews. Picture: Getty Images

Victoria Premier Daniel Andrews. Picture: Getty Images

After weeks of escalating coronavirus cases, recent days have brought some much-needed optimism to Victoria.

Just 11 new cases of COVID-19 were detected in Victoria in the 24 hours to Monday, the lowest number of cases in more than three months.

It's a far cry from the more than 700 cases that were seen in just one day during July.

While the declining number of cases is evidence that lockdown measures in Melbourne are working, there's still some way to go before some of those restrictions can be relaxed.

What is the road map out?

Lockdown restrictions for those living in Melbourne are on track to be eased from September 28.

The progression to stage 2 of restrictions depends on the rolling 14-day average of new coronavirus cases dropping below 50.

After the 11 new cases recorded on Monday, that 14-day average now sits at 34.4.

If that trend holds the line by September 28, Melburnians will see public gatherings increase to five people, provided they are from a maximum of two households, while schools will see a staged return to face-to-face learning.

However, people will still be restricted to travelling within 5 kilometres from their home and a curfew of 9pm to 5am will still be in place.

The third stage of the road map can begin from October 26 at the earliest and only when the rolling 14-day average across the state is less than five and there are less than five cases in the last 14 days that have an unknown source.

At that point, there will be no restrictions on leaving home and the number of people that can gather in one place can increase to 10.

Hospitality can also reopen to customers as well as all retail except for personal care services such as hairdressers.

The final stage can be implemented only after November 23, provided that there are no new coronavirus cases in Victoria for 14 days.

When that does happen, public gatherings can increase further to 50 people and up to 20 visitors are allowed in one home at one time.

Galleries, museum and other entertainment venues will be allowed to reopen with restrictions in place.

Regional Victoria is currently on stage 3 of reopening, with schools allowed to reopen to students and all retail is open.

When will Victoria reach zero cases?

Health experts have said it's only a matter of time before the state records no new cases in a single day.

While that prospect was almost unthinkable at the height of the spike of new cases, University of New South Wales epidemiology professor Mary-Louise McLaws said the low number of cases now will decline further in coming weeks.

"I think that they will get there," Prof McLaws said.

"Victoria has another 35 days to continue to have the decline in numbers to reach less than five new cases a day. The government there is taking all of the correct steps."

While zero new cases in the state is the optimal outcome, Prof McLaws said keeping new case numbers below five a day was also just as effective.

"For this particular virus with high infectivity, less than five cases per day is being close as close to elimination and a safe level," she said.

Australian National University infectious diseases expert associate professor Sanjaya Senanayake said the first day of zero new cases could be close.

"It's hard to say but it may take a bit more than a week," he said.

"The other thing with COVID is that it throws curveballs, so you never know, another outbreak might occur."

Does this mean the second wave is over?

Despite low case numbers, Victorians are being warned not to let their guard down.

Professor Senanayake said while the spike in cases in Victoria was decreasing, the second wave was not yet over.

"The outbreak is still going on, but it is heading back to where Victoria was in May where there was a small number of cases," he said.

"I would say the outbreak is getting under control."

However, of greatest concern to health authorities is the number of new cases where the source of infection was not able to be identified.

Professor Senanayake said those cases posed the biggest problem for contact tracing teams.

"They need to get on top of those cases, because from a practical point of view, you don't want too many cases with an unknown source because that source could still be out there and infecting others," he said.

What virus statistics are most important in tracking the outbreak?

While the number of new daily cases is keenly anticipated to see how the virus situation is unfolding, health experts have said it's not the only measure that should be monitored for how Victoria is tracking.

Prof McLaws said the rolling 14-day average gave the best picture as to how coronavirus was spreading across the community in Melbourne.

She said the rolling two-week average also was the best indication as to whether restrictions could be lifted for those in greater Melbourne.

"The 14-day average from an outbreak management perspective looks at the incubation period [for the virus]," Prof McLaws said.

"Victoria is on track to have achieved what NSW has achieved in managing coronavirus, which is a very fine thing to achieve.

"It means that human resourcing can cope with really good contact tracing."

This story What next for Melbourne's lockdown? first appeared on The Canberra Times.