Coronavirus: Why death and mortality rates differ
In Italy, an epicentre of the new coronavirus outbreak, the death rate at the end of March stood at a sobering 11%. Meanwhile in neighbouring Germany, the same virus led to fatality rates of just 1%. In China, it was 4%, while Israel had the lowest rate worldwide, at 0.35%.
At first it can seem surprising that the same virus – which doesn’t seem to have mutated significantly as it has spread – can lead to such widely differing reported mortality rates. And even within one country, the rate appears to change over time. So what’s going on?
Several main factors account for much of the difference we’re seeing – and perhaps the most important come down to simply how we’re counting, as well as testing, cases.
Differing death rates
First, there is confusion about what people mean by “death rate”. This confusion can make countries’ numbers look vastly different, even if their populations are dying at the same rate.
There are, in fact, two kinds of fatality rate. The first is the proportion of people who die who have tested positive for the disease. This is called the “case fatality rate”. The second kind is the proportion of people who die after having the infection overall; as many of these will never be picked up, this figure has to be an estimate. This is the “infection fatality rate”...
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