The proportion of people who die after being infected by the coronavirus has become highly controversial. Some have claimed that death rates aren’t as high as thought and that governments are overreacting by imposing measures such as lockdowns. But a recent meta-analysis confirms earlier estimates, finding that the death rate can be as high as 16 per cent for people over 90 but 0 per cent for children under 4.
This study concludes that in high-income countries, more than 1 in 100 people infected by the coronavirus died in the first wave. “The death rate is at least 10 or 20 times higher than flu,” says Nicholas Brazeau at Imperial College London.
More of the people admitted to hospital with covid-19 are surviving now, suggesting that the death rate has fallen slightly. However, if hospitals in some countries are overwhelmed during the surge of infections now hitting Europe and the US, that might not continue to be the case.
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Estimating the real death rate is hard for two reasons. First, the odds of dying from covid-19 vary greatly depending on a person’s age, sex, health and the standard of care received. This means death rates will vary from place to place and at different times.
For instance, the death rate is highest in care homes: in nursing homes in Belgium, one study estimated. In countries such as South Korea that have managed to largely prevent outbreaks in care homes, the overall death rate is lower. Similarly, vaccines that prevent severe disease in older people should reduce death rates.
The second reason it is hard to estimate the real death rate is that there is great uncertainty about the numbers used to calculate it. What we want to know is how many people who get infected with the virus actually die: the infection fatality rate.
The best way we have of working out how many people have been infected is to test the blood of thousands of people to see how many have antibodies to the coronavirus, and then extrapolate those results to entire countries. But antibody surveys can produce misleading results.
The number of confirmed cases that countries report can’t be used to calculate the infection fatality rate because most cases aren’t detected, because not everyone has symptoms, and not all who do get tested. Estimates suggest that about 250,000 people were infected daily at the peak of the first wave in the UK, when only 5000 daily cases were being reported by the government.
For high-income countries, we do have a fair idea of how many people have died but there are still uncertainties. In the UK, for instance, many deaths were missed at the start because of the lack of testing, so the official estimate of around 44,000 in the first wave is too low, says Paul Hunter at the University of East Anglia in the UK.
“The 44,000 number underestimates the total mortality quite substantially,” he says. “A lot of deaths were not diagnosed early on.” Looking at the number of deaths above what was seen under “normal” conditions in previous years suggests that 10,000 or even 20,000 deaths were missed.
In lower-income countries, most covid-19 deaths are probably unreported. For instance, in Damascus, Syria, according to that country’s data.
For all these reasons, reported infection fatality rates have varied widely. To get a better estimate, Brazeau and his team looked at 175Â studies, finding just 10 they regarded as reliable. They adjusted for confounding factors and calculated the death rate for each age group: less than 0.1 per cent for people under 40, 0.36 per cent for people aged 50 to 54, 2.17 for people aged 70 to 74 and 5 per cent and higher for those 80 or above.
During the first wave, the infection fatality rate in high-income countries, which tend to have a high proportion of older people, was just over 1 per cent, . For countries with younger populations, it would have been 0.2 per cent, assuming the same age-specific death rates – which may not be the case given the poorer healthcare in many of these countries.
The death rate should be lower now because healthcare workers have more experience treating covid-19, and trials have revealed which treatments are effective. Data from hospitals in England, Wales and Northern Ireland show that people admitted with covid-19 after 1 September were about 10 per cent less likely to die than those admitted before then.
“There is evidence that fatality rates in hospital have been improving over time, but more work is needed to fully understand these patterns,” says Robert Verity at Imperial College London. Fewer people infected during the current waves in the US and Europe are expected to die, but this will not be clear for a while – because most of the deaths haven’t happened yet.
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