Ten weeks later,with just 103 COVID-19 deaths,some experts say the modelling behind the national cabinet's decisions was flawed and some commentators say the response went too far.
![Chief Medical Officer Professor Brendan Murphy said Australia had avoided 14,000 deaths by implementing strict social distancing measures.](https://static.ffx.io/images/$width_300%2C$height_150/t_crop_auto/t_sharpen%2Cq_auto%2Cf_auto/7916ae5bdc20e12b1ab67e306f0ea5ad06037a5b)
Chief Medical Officer Professor Brendan Murphy said Australia had avoided 14,000 deaths by implementing strict social distancing measures.Alex Ellinghausen
When Prime Minister Scott Morrison announced a ban on mass gatherings of more than 500 people on March 13,Australians seeing widespread lockdowns imposed overseas began to ask for the modelling that lay behind the national cabinet's decisions.
Two days later,Deputy Chief Medical Officer Paul Kelly was quizzed about the expected numbers at a press conference in Canberra,and.
"The death rate is around 1 per cent. You can do the maths,"Professor Kelly said,urging the public to avoid large gatherings. The maths worked out to between 50,000 and 150,000 deaths.
On Tuesday Chief Medical Officer Brendan Murphy by implementing strict social distancing measures,considerably fewer than the initial warning.
Grattan Institute health economist Stephen Duckett said the dramatic variation between the estimates of potential deaths came down to the difference between taking no action to prevent the virus spreading and taking only limited action.
"The estimate of deaths in those early days,they assumed no lockdowns and no action,"Dr Duckett said.
"If you let the disease rip,you'd have a huge number of deaths."
UNSW Business School professor of economics Gigi Foster,who has been a vocal critic of the decision to lock down,said the small number of deaths vindicated her argument governments had gone too far.
"That's an order of magnitude lower than what the modelling initially expected,"Professor Foster said,warning models that over-estimated the spread could mean blanket restrictions that were"far more costly"than they needed to be.
ANU infectious diseases professor Peter Collignon said the modelling prepared for the government by the Doherty Institute released in April was also flawed as it assumed that every person infected would pass it on to 2.5 others on average.
Professor Collignon also took issue with the assumption people's behaviour would not change as the risk of interacting with others became clear,something he dubbed"unrealistic".
Prime Minister and the figures were based on a combination of Chinese and international data as Australian community transmission was too low to give a full and accurate model.
Scott Morrison says international modelling of the coronavirus has helped flatten Australia's curve but now is not the time to be complacent and undo all the hard work.
The Doherty Institute modelling,which showed how intensive care units would be quickly overwhelmed if social distancing measures were not implemented,made no reference to a potential 150,000 deaths or of 60 per cent of the population becoming infected.
The 60 per cent spread was a scenario being discussed by global health experts and governments in March after the,which sparked debate over whether the virus should be allowed to spread.
Professor Kelly attributed the 60 per cent figure to German Chancellor Angela Merkel and the lower estimate of 20 per cent to NSW chief health officer Kerry Chant.
While the Doherty Institute's modelling warned 70 per cent of patients needing an ICU bed could be turned away without social distancing measures,on Wednesday just 30 COVID-19 patients were in hospital,with six in intensive care and only three on ventilators - while the government has more than doubled the nation's ventilator capacity to 7500.
The expert modellers from the Doherty Institute have defended their work against accusations it overestimated the risk of COVID-19 to Australia.
Professor James McCaw last week the modelling didn't overestimate the risk;"Rather it underestimated society's ability to respond and prevent transmission".
The institute was not asked to model how the virus would spread under the lockdown measures put in place after it was drawn up.
Professor Jodie McVernon from the Doherty Institute said the modelling was based on the assumption that"only fairly modest levels of social restriction to reduce transmission would be achievable in Australia".
The public buy-in of physical distancing,hygiene,isolation and quarantine measures had reduced the spread"beyond initial expectations",she said.
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University of Melbourne professor of epidemiology Tony Blakely,who is on an expert panel advising the federal government on its COVID-19 response,said modelling at the beginning of the epidemic was"scenario based"and the Doherty Institute's modelling had assumed borders would stay open for longer.
Rachael Brown,director of the ANU's Centre for Philosophy of the Sciences said,the lack of Australian data was a"major challenge"for modellers in April when much of the information was from the spread of the virus in China.
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"It is a different context to Australia[in Hubei],it's more urban,there are multi-generational families[living together],"Dr Brown said.
"Unique factors play into what goes on,"she said.
"It's hard to know how people are going to behave ... This is really hard to capture in a model."
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