Ross Clark Ross Clark

How deadly is Covid-19?

(Photo by Christopher Furlong/Getty Images)

What percentage of people who are infected with Covid-19 will go on to die of the disease? The dramatic response to the pandemic on the part of almost all governments around the world has been based on the idea that Covid-19 is a far more lethal disease than seasonal flu, which is often quoted as having an infection fatality rate (IFR) of 0.1 per cent. The World Health Organisation (WHO) is often quoted as claiming that Covid-19 has an IFR of 3.2 per cent — a claim that goes back to a press conference in early March when it, in fact, said that the case fatality rate (CFR) at that stage was 3.2 per cent. 

The CFR is the division of known deaths by known cases — the denominator omitting the many cases that have not been confirmed by diagnosis. In a disease where large numbers of people are asymptomatic, the case fatality rate is bound to differ widely from the infection fatality rate.

Estimates of the IFR for Covid-19 have tended to settle in the range of 0.5 per cent to 1 per cent. The Imperial College paper of 16 March, which did so much to inform UK policy on Covid by predicting that 250,000 people could die unless the government introduced stricter social distancing measures, assumed an IFR of 0.9 per cent. A subsequent Imperial College study put it at 0.66 per cent.

Now, John Ioannidis of Stanford University has produced perhaps the most comprehensive attempt to estimate the IFR for Covid-19 to date. In a peer-reviewed study published in the Bulletin of the World Health Organisation he looked at 61 studies from around the world that have tried to measure the true prevalence of Covid-19 through serological studies.

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