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Why we still don’t know what the death rate is for covid-19

UK ambulance

Death rates from covid-19 differ around the world

Victoria Jones/PA Wire/PA Images

What are your chances of dying if you get infected by the coronavirus? Despite data pouring in many countries, there’s still a wide range of estimates, from as few as 1 in 1000 to as many 1 in 30.

What is clear is that there is no one answer: the risk depends on your age, your sex, your health and the care you receive if you become severely ill. In other words, death rates will vary from place to place and over the course of the pandemic.

In the UK, as of 2 April, 2921 people had died out of 33,718 confirmed cases – a crude case fatality rate of around 9 per cent. For Italy, the figure is nearly 12 per cent and for Germany just 1 per cent.

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These figures do not tell us what we really want to know: how many of those infected will die as a result, which is known as the infection fatality rate.

Crude case fatality rates are so-called because they do not take into account the fact that some of those who have tested positive will go on to die. Early in March, for instance, South Korea had a crude case fatality rate of just 0.6 per cent. That has risen to 1.7 per cent. Among resolved cases – those who have died or recovered – the case fatality rate is 2.9 per cent.

The differences between countries are also partly to do with how many elderly people have been infected, says Melinda Mills at the Leverhulme Centre for Demographic Science in the UK. In South Korea and Germany, it was mostly younger people infected at first.

Based on what’s happening in Italy, Mills and colleagues calculate that if 10 per cent of people were infected, there would be 302,530 deaths in Italy in with its ageing population of 61 million – but just 142,058 deaths in Nigeria with its much younger population of 191 million.

The big question is how many infected people with mild or no symptoms are being missed. If lots are, the infection fatality rate will be much lower than the case fatality rate. We know the UK is testing only severely ill people and missing lots of mild cases, but South Korea and Germany have been testing more widely.

Neil Ferguson’s team at Imperial College London has estimated the number of missed cases based on how many people evacuated from Wuhan tested positive. They conclude that the infection fatality rate in China is 0.66 per cent.

Julien Riou of the University of Bern in Switzerland instead assumes all covid-19 cases among people over 80 are being detected. His team estimate that the infection fatality rate in Italy is 3.3 per cent, rising from 1 per cent among people aged between 50 and 59 to nearly 90 per cent in those aged 80 or above. For China and Spain, the overall rate is 3 per cent. If half of cases in those over 80 are being missed, it would halve these figures, Riou says.

At the other end of the spectrum, Jason Oke at Oxford University thinks not all of the deaths attributed to the coronavirus are caused by it. He points out that while there is an excess of deaths in Italy according to EuroMOMO, a public health monitoring organisation, it is not as large as that during the last bad flu season in 2016. His team thinks the infection fatality rate could be as low as 0.1 per cent.

But on 1 April, the EuroMOMO website had a highlighted warning about against drawing such conclusions based on its data. While that warning has since been removed, it still states that the “number of deaths in recent weeks should be interpreted with caution”.

What’s more, it has also been reported that one badly hit town in Italy called Nembro has reported 158 deaths so far this year compared with 35 on average each year for the past five years. Only 31 of the 158 deaths were recorded as due to covid-19.

So for now we still can’t say for sure what the infection fatality rates are. This will start to become clearer soon, as antibody testing reveals who has been infected in the past, and thus the number of missed cases.

Journal reference: Lancet Infectious Diseases, DOI: 10.1016/S1473-3099(20)30243-7

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