“While we didn’t empirically test how changes in the contact tracing system would affect case numbers, we did base the model around current Victorian contact tracing performance,” Dr Thompson said.
Premier Daniel Andrews cited the expert modelling to justify the state’s “safe, steady and sustainable” road out of lockdown, warning that Victoria had a 60 per cent chance of returning to lockdown by Christmas if restrictions were eased too early.
Prime Minister Scott Morrison responded by saying that he hoped Victoria’s road maps out of restrictions were a “worst-case scenario” that could be improved if Mr Andrews enhanced the state’s contact tracing systems.
Victorians will not return to anything resembling normal life until late November under the state’s road maps, which chart a gradual easing of restrictions starting on September 28, with further easing reliant on case numbers lowering to a fortnightly average of five per day, then zero cases after that.
Victoria reported 55 new cases on Tuesday and eight deaths.
The current 14-day average for metropolitan Melbourne is 78.6, down from 84.8 on Monday. For regional Victoria it is 4.9, down from 5.3.
In Melbourne, the target to start easing restrictions is 30 to 50 cases.
Victoria’s Chief Health Officer Professor Brett Sutton admitted on Tuesday that Melbourne’s unique overnight curfew was not a public health measure recommended by him or based on medical advice, but said it had “probably” been a useful tool.
Health Minister Greg Hunt continued the federal government’s criticism of the Victorian government on Tuesday, saying Canberra was yet to be given all the information behind the projections.
“We’d like to see all of those details of the modelling released. Not just to the Commonwealth, but to the public in terms of the assumptions, the predictions, the basis for it,” Mr Hunt said.
Doherty Institute epidemiologist Professor Jodie McVernon said Victoria may never reach the goal set by the government of zero cases over a fortnight, while business leaders accused the government of failing to properly consult with industries and their COVIDsafe proposals.
Mr Andrews revealed a series of measures to enhance contact tracing on Tuesday, including new local contact tracing response units and the deployment of a team of government experts, including Australian Chief Scientist Alan Finkel, which will travel to NSW to glean public health improvements.
The Victorian government’s projections, prepared by researchers from Melbourne University and the University of New England, suggested case numbers would begin to rise again in early November if stay at home restrictions were lifted while Victoria has a fortnightly average of above 25 cases per day.
A Victorian government spokesperson said: “The modelling reflects current Victorian data, however we will continually update our modelling into the future based on the most up to date evidence.”
Professor Catherine Bennett, Deakin University’s chair in epidemiology, said that risk could be significantly lower if it took ongoing improvements in contact tracing into account.
“Each parameter in a model drives the model. If you overestimate how long people are in the community and infectious, by underestimating the efficiency of contact tracing, then that potentially changes your outputs dramatically,” she said.
“You will alter the likelihood of having a resurgence before Christmas, and you will alter the threshold numbers that keep you in a safe range. It impacts that story about risk [of a third wave], and it impacts the sweet points that you come up with to tell you how many cases you can safely manage with your contact tracing system.”
Under the Victorian government’s road maps, a 9pm curfew and bans on home visits will be applied until the state has a 14-day average of five or less cases per day. The government has slated this to happen by October 26, but said it could happen earlier if case numbers are driven down.
The Prime Minister on Monday suggested that threshold could be increased if Victoria improved its contact tracing.
“NSW is the gold standard. That is where we have to get everybody to, to ensure that Australia can be open,” Mr Morrison said.
A government spokeswoman said Victorians could beat the road maps by adhering to public health guidelines.
“Victoria’s contact tracing system is already comparable with NSW, nationally agreed benchmarks and world’s best practice, which is reflected in the model,” she said.
Professor Sutton revealed on Tuesday that it was not his decision to implement an 8pm curfew in Melbourne as part of stage four restrictions.
“It wasn’t something I was against from a public health perspective. I was consulted on it, but it was a separate decision-making pathway,” he said on 3AW radio.
Asked if he would have introduced it, the Chief Health Officer said “I’m not sure”.
“I hadn’t reflected on it. I think it has been useful. So if I put my mind to it, probably [yes].”
Michael is a state political reporter for The Age.