EXPLAINER

Explainer: When will Victorian lockdown lead to decline in coronavirus case numbers?

Victoria is halfway through a second six week lockdown due to coronavirus. Picture: Shutterstock
Victoria is halfway through a second six week lockdown due to coronavirus. Picture: Shutterstock

Three weeks ago Greater Melbourne and Mitchell Shire residents were plunged into a second lockdown, only allowed to leave home for essential reasons for six weeks.

Community transmission had been on the rise in the state for weeks, prompting the Victorian government to impose tighter restrictions on high-risk postcodes first in a bid to prevent the city-wide lockdown.

Two-weeks into the state's second lockdown, Victoria hit a record 484 new infections which was quickly superseded.

On Monday, a new record of 532 cases was reported in a 24-hour period, followed by 384 on Tuesday.

Despite a growing caseload and death toll, experts say the situation would be far worse if strict measures hadn't been taken.

Why are daily case numbers still rising three weeks into lockdown?

Dr Meru Sheel from ANU's National Centre for Epidemiology and Population Health said it was too soon to see the effects of lockdown.

The incubation period of coronavirus is up to 14-days. Authorities have been using that marker throughout the pandemic to determine how effective restrictions have been.

"The cases you are now seeing in week three are essentially people who were infected in week one or even before that if there was delayed presentation," she said.

"Because of the long incubation period and people presenting late those act as contributors to any kind of delay that you might see.

"By the time the lockdown [started] there was already a lot of cases and we know the disease can have an incubation period of up to two weeks, for any intervention to take shape it's going to take a minimum of two to four weeks."

When will new infections start to decline?

Dr Sheel said if the restrictions had been effective, new cases could begin to slow by next week.

However, that is dependent on a couple of things.

"Unless and until sick people stay at home we're not going to see any change in the course of the outbreaks," she said.

Victorian Premier Daniel Andrews said on Monday lockdown would not end if people continue to go work sick, which "far too many" were doing.

Dr Sheel said it was difficult to predict how case numbers would shape up in the coming weeks.

"You'll only see a number change if interventions are having an impact, so if we're able to break the chain of transmission," she said.

"Victoria has a lot of clusters at the moment ... the fact they can identify cases by clusters is an excellent thing from a public health response point of view."

What is the reproductive rate in Victoria?

The reproductive rate or "R" number is used to determine how infectious a disease is.

Health authorities want that number to stay below one, which indicates lower transmission.

Victorian chief health officer Brett Sutton said the R number was calculated twice a week and expected it was now "very close to one, if not below one".

"So there should be a downward pressure on transmission in the community but, again, whenever you have a setting that allows for significant outbreaks to occur that can also drive that R number up," he said.

Professor Sutton said the state's current cases were "very much driven by outbreaks".

"We need to get on top of the outbreaks, make sure they are not being seeded by community members with ongoing transmission."

Has Victoria started to bend the curve? 

Victorians are likely hopeful to bend the curve next week and see a decline in numbers, Dr Sheel said, but it was too soon to know for sure.

"It's hard to predict whether things will change next week or in two weeks time," she said.

"If they change, they are a reflection that the interventions are working, but if we don't see the numbers change that means we need to tweak the interventions."

How effective are mandatory face masks? 

Dr Sheel said the primary purpose of face masks was source control.

"When you don't know how many people are infected it makes sense that infected people preemptively are asked to wear a mask," she said.

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"By people wearing masks, anybody who is infected is going to spread it to fewer people."

She expected it would take at least two weeks before the effect of masks on the transmission rate could be understood.

Will a longer lockdown be needed? 

Victoria's second lockdown has been slated to run for six weeks, which Dr Sheel said was a good "trial time".

That period represents three incubation cycles of COVID-19 and would allow health authorities to understand how effective the measures had been at the end of it.

"If the transmission has a strong foothold and the community doesn't support the public health response then it's not going to lead to a change," Dr Sheel said.

"We really do need sick people to stay at home and get tested.

"The community has to buy into the lockdown, as challenging as it might be."

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This story Why are Victorian case numbers still rising halfway through lockdown? first appeared on The Canberra Times.

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