One of the great unknowns of the COVID-19 crisis is just how deadly the disease is. Much of the panic dates from the moment, in early March, when the World Health Organization (WHO) published a mortality rate of 3.2 percent — which turned out to be a crude ‘case fatality rate’ dividing the number of deaths by the number of recorded cases, ignoring the large number of cases which are asymptomatic or otherwise go unrecorded.
The Imperial College modeling, which has been so influential on the UK government, assumed an infection fatality rate (IFR) of 0.9 percent. This was used to compute the infamous prediction that 250,000 Britons would die unless the government abandoned its mitigation strategy and adopted instead a policy of suppressing the virus through lockdown. Imperial later revised its estimate of the IFR down to 0.66 percent — although the March 16 paper which predicted 250,000 deaths was not updated.
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