Sydney's outbreak will 'NEVER be as bad as Melbourne' but the city is on a 'dangerous knife-edge' when it comes to controlling the spread, warns Dr Norman Swan

Sydney's current coronavirus outbreak will never be as bad as Melbourne's second wave as Victoria had poor contact tracing systems, according to Dr Norman Swan.

The ABC presenter told Channel Ten's The Project that although New South Wales reported a record number of cases on Thursday with 239 new infections, the daily totals will likely always fall short of the more than 700 cases that were being racked up in Victoria nearly a year ago. 

Dr Swan said that Victoria's poor contact tracing left the state powerless to stop the virus spreading, while an influx of vaccines - not available last year - gives Sydney a fighting chance at containing case numbers.

But the physician warned Sydney's spirally outbreak remains 'on a knife's edge and  could slip out of control' if contact tracing fails and vaccination rates don't improve.

'It is a different situation in NSW, because Victoria did not have an effective contact tracing system. NSW does. So they've held it in check,' Dr Swam bluntly explained. 

Sydney's current coronavirus outbreak will never be as bad as Melbourne's second wave, according to Dr Norman Swam. Pictured: Flinders Street Station in Melbourne on November 22, 2020, when the city emerged from its 112-straight day lockdown

People queue to receive the Covid-19 vaccine at Sydney Olympic Park on Thursday - with experts saying higher jab rates may release millions from lockdown

'It's true when the Premier says they've saved a lot of cases and it is hard to know how many, but it will be many thousands of cases because of their contact tracing systems, that's number one. 

'Number two is that vaccination is coming in albeit at a very slow rate.'

He said the Gladys Berejiklian government is betting their contact tracing teams can 'hold the fort' while vaccinations are ramped up across Sydney hotspots.

But with the outbreak now growing exponentially with an R-rate above one, Dr Swam said the situation is 'precarious'. 

'The only thing that works in this is social distancing and human behaviour change,' he said. 

'So it's on a knife-edge and it could slip out of control.'

A pedestrian strolls down the iconic Hosier Lane in Melbourne on November 22, 2020 as the city emerged from its 112-day lockdown

Shoppers are seen in the Royal Arcade in Melbourne on November 22, 2020 as the city's Covid finally restrictions eased

But NSW contact tracers once labelled the 'gold standard' by Prime Minister Scott Morrison, have been facing immense pressure to keep up with the relentless surge of cases and exposure sites this time around.

Health officials revealed on Thursday they have not been able to pinpoint the origin of 779 Covid infections. 

In fact, there are still 118 cases from the first two weeks of July that remain a mystery and are continuing to be under investigated.

One woman who shopped at the Campsie Shopping Centre which was exposed to the virus for an an 11-day stretch was not contacted by NSW Health for four days despite being a close contact. 

While Covid detectives were quick to inform staff at the Tong Li supermarket, where the infected person worked, shoppers and neighbouring stores were mostly left in the dark raising concerns contact tracers in NSW are overrun.

Justin Leach, who is currently in isolation with his wife, said the information was already circulating on social media well before NSW Health reached out.

'We found the time lag from when my wife had attended the supermarket to when we were being notified a bit concerning, particularly as the information had been circulated on social media earlier, which we ignored. So we were concerned at the delay,' Mr Leach told 7.30.

Sydney Airport is pictured completely deserted in the midst of Covid lockdown on Thursday with experts saying that without efficient contact tracing, the city's outbreak could spread out of control

Traveller are pictured in full protective gear as they pick up their baggage at Sydney on Thursday in the midst of Covid lockdown

Dr Swan added that while vaccinations hold the key to getting out of lockdown and reducing the number of daily cases, he warned it will be some time before most Australians are able to get the potentially life-saving jab. 

'We are not going to get there terribly quickly in Australia - maybe March of next year to 80 per cent (national vaccination rate),' he said.

'We will only be at 50-60 per cent by Christmas'.

He warned that if Australia is to eventually do away with lockdowns the vaccination rate may need to be as high as 90 per cent as UK studies have suggested.

'The true number of people who just don't want to get vaccinated ever is about probably just under 10 per cent,' Dr Swan said.

'So 90 per cent of Australians will have a vaccine if it's made convenient and they're convinced that it is safe and they're motivated to do so.'