Coronavirus could "die out" in Australia entirely if New South Wales and Victoria stay on their current trajectory of low infections, according to two leading epidemiologists.
Key points:
- Victoria had seven days of zero COVID-19 cases this week
- The NSW chief health officer said the virus may have been eliminated once in Sydney already
- Data has shown that when cases climb over 40 a day, contact tracers become swamped
The two states are responsible for 90 per cent of the country's COVID-19 cases and 96 per cent of deaths.
But as new infections flatline in Victoria after a months-long lockdown, and cases dwindle in NSW amid rampant contact tracing, some experts have now admitted COVID-19 could be eliminated in Australia, despite the fact it has never been the national strategy.
Yesterday Victoria recorded its seventh straight day of no new cases and NSW has recorded nine cases since Monday.
Hassan Vally, an epidemiologist from La Trobe University, said new infections should continue to be contained.
"NSW is the model, we have a low number of cases, the public health response stamps on any clusters and you keep everything under control," he said.
"No-one knows what will happen over the next week in Victoria, but it's not outside the bounds of possibility that we will see zero cases for another week or so and then technically we've eliminated the virus."
Suppression, rather than elimination, was the goal of Victoria's stage-four lockdown, while NSW Premier Gladys Berejiklian has long maintained residents must learn to live with COVID-19 until a vaccine is found.
Catherine Bennett, chair of epidemiology at Deakin University, said while "thin lines" of transmission could still happen, it was also possible that COVID-19 dies out in Australia.
She said the key was tracing known cases.
"Every time we do that, we are narrowing down and getting rid of another little set of chains of transmission," Professor Bennett said.
"Even if the virus is out there, it is more likely to die out than spread."
Earlier this week, Ms Berejiklian said NSW Health modelling showed Victoria may have eliminated coronavirus.
"They may have, because of the lockdown, actually gone down a path of having eliminated it at this point in time," Ms Berejiklian said.
At the same press conference, NSW chief health officer Kerry Chant said COVID-19 had likely already been eliminated once in Sydney already before a cluster sparked by an infected worker from Victoria spread at the Crossroads Hotel in Casula.
"Our data suggests we did not have any circulating virus until we had the seeding event back in late June early July," Dr Chant said.
Flattening the curve, again
Australia's two most populous states have been on very different COVID-19 trajectories throughout the pandemic.
The ABC has charted the key coronavirus moments, from the Ruby Princess docking in Sydney on March 19, to the day Melbourne's public housing towers were shut down as the Victorian Government desperately tried to contain the second wave.
These graphs outline how, by the third week of May, lockdowns in NSW and Victoria had successfully flattened their curves.
Professor Bennett said that should have been a turning point for Victoria.
"We got down to 10 cases a day, that should have been manageable, even with our antiquated contact tracing systems we did shut that [transmission] down, even though we had some new cases emerging," she said.
However, on May 27, a staff member at Rydges Hotel on Swanston in Melbourne tested positive for the virus, sparking a "multi-site seeding event" that eventually lead to Victoria becoming Australia's worst-affected coronavirus state.
Victoria's situation also lead to a return of the virus in NSW, when an infected transport worker from Melbourne visited the Crossroads Hotel on July 3.
The cluster, discovered two days after the NSW-Victoria border was closed, would eventually grow to 57 people.
However, according to Professor Bennett, NSW had one crucial advantage in suppressing its second wave — a "heads up".
"With the second wave taking off [in Victoria], NSW were waiting for the virus to jump the border and they jumped on it," she said..
During their respective second waves, the focus in NSW and Victoria has been on tracing mystery coronavirus cases — where someone tests positive to COVID-19, but the source of their infection remains unknown.
Dr Vally said once the case numbers reach a certain level, contact tracing can't keep up, no matter how good the public health system is.
This chart shows the difference between total case numbers, mystery case numbers, and the final tally of mystery cases in the Victorian second wave.
The data shows that when cases climbed over 40 a day, more and more cases were classified as having an unknown source or were under investigation, as contact tracers became swamped.
It was not until the middle of September, when daily case numbers were again averaging around 38, that the number of mystery cases fell under 10.
In NSW, the number of mystery cases peaked at 28 on April 1, but from then on it was rarely over 10 per day.
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2020-11-06 20:28:00Z
CBMicGh0dHBzOi8vd3d3LmFiYy5uZXQuYXUvbmV3cy8yMDIwLTExLTA3L2Nvcm9uYXZpcnVzLWNvdWxkLWJlLWVsaW1pbmF0ZWQtaW4tYXVzdHJhbGlhLWVwaWRlbWlvbG9naXN0cy1zYXkvMTI4NTExNTLSASdodHRwczovL2FtcC5hYmMubmV0LmF1L2FydGljbGUvMTI4NTExNTI
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