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Victoria’s reopening model says hospitals will be overwhelmed. Is it right?

“Then in the last couple of days, the numbers in Victoria have kept trucking up. I think they are overestimating the likely health harms, but it’s fairly good.”

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Other models are more optimistic.

The Doherty Institute projects 914,357 cases Australia-wide, with 35,322 hospitalisations, 7611 ICU admissions and 6402 deaths over six months.

The University of Melbourne, looking just at 2022, projects a fraction of that: 200 ICU admissions and 250 deaths. However, the trade-off would be Victorians spending about 14 per cent of the year in lockdown.

Despite the differences between the models, several independent teams told The Age their data was starting to say the same thing: reopening at a vaccination rate of 80 per cent would mean high levels of infection, hospitalisation and death unless other restrictions are put in place.

“All the models are converging at this point,” said Dr Jason Thompson of the University of Melbourne, who worked on the Victorian government’s epidemic modelling. “They are all converging on a vaccines-plus strategy.”

The other key difference is that the Burnet’s modelling is the only one to incorporate new and higher mortality rates from the Delta strain of COVID-19.

The Burnet’s model is also more pessimistic than the Doherty’s about how well vaccines stop people passing on the virus, although it does not model waning immunity.

“We need to be thinking about booster shots now because there is mounting evidence of waning efficacy,” said Will Mackey, a senior associate at the Grattan Institute.

The Burnet’s model puts the current effective reproduction number – the average number of people each infected person passes the virus to – about 1.6

University of South Australia biostatistician Professor Adrian Esterman estimated that number had hovered near 1.2 this week, with a sudden blip on Thursday when the state recorded 766 cases.

“That could be an artefact of testing, just random variation, or even the impact of the weekend’s protest marches starting to kick in,” he said.

The question is how high case numbers can get before vaccines start bending the curve, as they have now done in NSW.

That state saw its transmission potential fall from 1.62 on August 19 to 0.9 a month later. The same is starting to happen in Victoria, the number falling from 1.79 to 1.15 over the same period.

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“That’s almost entirely due to the vaccine rollout,” said University of Melbourne’s Professor James McCaw, who has tracked that data for the federal government.

“We’re seeing the transmission potential reduce in Victoria as well, due to the vaccine – it’s just a little bit higher. The vaccine is a little behind in Victoria compared to NSW.

“I would anticipate, over the coming weeks, Victoria’s transmission potential would get very close to 1, if not drop under 1.”

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