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The awful arithmetic of herd immunity

Summary:
The ABC has an article quoting University of Melbourne epidemiologist Tony Blakely as saying (approvingly) that the object of the current “flattening the curve strategy is to smooth the path to herd immunity. Key quotes You don’t go in too hard because you actually want the infection rate to pick up a bit and then hold,” he said. “What they’re not saying is [that] ‘flatten the curve’ likely means [that] by the time this is over, 60 per cent of us will have been infected, to develop herd immunity,” he said. The arithmetic here is pretty horrifying. 60 per cent of the population is 15 million so with a 1 per cent fatality rate, that would be 150 000 deaths. The number surviving but with long-term lung damage could easily be over 1 million. It gets even worse. If herd

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The ABC has an article quoting University of Melbourne epidemiologist Tony Blakely as saying (approvingly) that the object of the current “flattening the curve strategy is to smooth the path to herd immunity. Key quotes

You don’t go in too hard because you actually want the infection rate to pick up a bit and then hold,” he said.

“What they’re not saying is [that] ‘flatten the curve’ likely means [that] by the time this is over, 60 per cent of us will have been infected, to develop herd immunity,” he said.

The arithmetic here is pretty horrifying. 60 per cent of the population is 15 million so with a 1 per cent fatality rate, that would be 150 000 deaths. The number surviving but with long-term lung damage could easily be over 1 million.

It gets even worse. If herd immunity is supposed to be achieved over 12 months (by which time we are hoping for a vaccine) that would imply 40 000 new cases every single day. If even 10 per cent required hospitalization for several weeks, they would fill every bed in the country.

As for intensive care, we have a total of just over 2000 beds. Even with a hospitalization rate of 1 per cent, they’d be full in five days. And given that 1 per cent is the estimated fatality rate with treatment, that implies triage on a massive scale, which in turn would greatly increase the death rate.

This is simple arithmetic. If Blakely’s explanation of the government’s strategy is correct, it should be spelt out.

John Quiggin
He is an Australian economist, a Professor and an Australian Research Council Laureate Fellow at the University of Queensland, and a former member of the Board of the Climate Change Authority of the Australian Government.

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