As Melbourne endures one of the world’s harshest current lockdowns, infectious diseases experts warn there is one main factor protecting the rest of Australia from the same fate.

After someone has a confirmed case of COVID-19, contact tracing teams race to conduct in-depth interviews with all the people that person may have seen over the past week, and tell them to isolate.

Sydney and other Australian cities aren’t immune from Melbourne’s current situation. Photo: AAP

In most states and territories, case numbers are so low that it is still possible to trace all coronavirus cases back to the origin.

But Victoria, with a seven-day average of nearly 500 new coronavirus cases each day, the task of tracing them has become too difficult.

It comes as the state introduces tough new Stage 4 restrictions on businesses from midnight on Wednesday, with large swathes of the state’s manufacturing forced to close while others – including all Victorian meatworks – will have to scale back production.

Victoria reported another 439 new COVID infections and 11 deaths on Tuesday, taking its toll from the pandemic to 147.

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How the rest of Australia can prepare

Dr Alex Polyakov, a senior lecturer in obstetrics and gynaecology at the University of Melbourne, said it was important to note contact tracers must be trained professionals – “not just someone from the street”.

“Before this pandemic, we had maybe 20 people in the whole state who could confidently do it,” he said.

NSW authorities managed to contain the Crossroads Hotel cluster. Picture: AAP

“Now you literally require hundreds, if not thousands, of tracers to trace every single person who is infected in Victoria, while in NSW it is still possible.”

But that doesn’t mean the rest of Australia is free to hug and shake hands.

“There is every possibility it may get out of control,” said Dr Polyakov, who holds a masters in epidemiology and biostatistics.

“Even though NSW has very few cases of community transmission, it’s still there. They haven’t extinguished it.”

Melbourne could be a global role model

For weeks, Victorians watched in horror as the state’s daily coronavirus cases soared until a second wave was declared.

But University of Queensland virologist Professor Ian Mackay said the sudden and widespread community transmission of COVID-19 was “not unique to Melbourne”.

“Places all around the world are seeing these flare-ups now,” he said, adding the “world was watching” to see if the Stage 4 lockdown would bring the virus under control.

“Anything in Melbourne that works can rest assured it will be adopted elsewhere because everyone is in desperate need of trying to find a way out of this.”

Professor Mackay added no Australian state or territory – “not even New Zealand” – was safe from a situation like Victoria.

“It only takes a few slips and this thing could get away from us,” he said.

“Once it starts to gain momentum and starts spreading among the community, and clusters become geographically distant, it becomes very hard to shut it down.”