From a Nine News report (March 16, 2020):

...it comes as our medical authorities predict that in the best case scenario 20% of the Australian population will be infected, that equates to around 5 million people...

There's a similar claim in The Australian (March 13, 2020):

Most experts are optimistic that Australia will be able to keep transmissions of COVID-19 to the low end of projections. But even the best-case scenario is grim: NSW’s Chief Health Officer predicted­ this week that 1.5 million people, or 20 per cent of the state’s population, will be infected. At a death rate of 1 per cent, that would mean 15,000 dead in NSW alone.

For a "best case scenario", it seems extreme, far worse than China. I'd like to see how they came to that conclusion.

Question: Is it realistic that "in the best case scenario 20% of the Australian population will be infected" by the novel coronavirus?

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    Merkel said 70% of Germans. I don't see how I could make a reasonable Skeptics question from something like that though. – Fizz Mar 17 at 12:09
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    At this stage no one knows. It depends as much on politics as it does on geography and weather. (And note that "best case scenario" is kind of like saying "In your dreams".) – Daniel R Hicks Mar 17 at 12:15
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    @Fizz, Merkel's worst-case scenario is simply taking the high estimate for the basic reproduction number of COVID-19, and calculating the epidemic equilibrium number from that. It's what would happen if no countermeasures whatsoever were taken -- not even basic ones like "wash your hands" and "stay home if you're sick". – Mark Mar 18 at 2:59
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    The best case scenario is the epidemic being stopped entirely (as it happened in China, although of course more outbreaks might happen there). Also, it's hard to envision a scenario where 20% of the population gets infected but the mortality rate stays at 1% (intensive care does not get overwhelmed). In China about 0.01% of the population got infected and mortality was way higher due to lack of hospital beds. – Tgr Mar 18 at 15:36
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