Get Covid and live longer? No, it doesn’t work like that

According to the BBC, on 15 October, the prime minister allegedly sent a WhatsApp message: “I must say I have been rocked by some of the data on Covid fatalities. The median age is 82 – 81 for men, 85 for women. That is above life expectancy. So get Covid and live longer.” Presumably, this was a joke, but why is the reasoning so wrong?

First, more technically, the message confuses two types of averages. As children learn at school, the median means that if you lined up the women according to the age they had died of Covid-19, the woman in the middle would be 85. But life expectancy is a mean-average – you work out how long, say, 100,000 newborns are likely to live assuming that current mortality rates continue, add them up and divide by 100,000. Using data from the UK for 2017-19, life expectancy at birth is 79 for men and 83 for women, but the median age at death is slightly higher: 81 for men and 85 for women, the same as that quoted for Covid-19.

So why do registered deaths involving Covid have a similar median age to deaths from other causes? Essentially, the risk factors for dying with Covid are remarkably similar to those for dying from something else – this bullying virus amplifies vulnerabilities and so roughly acts like a multiplication factor to background fatal risks.

Even more importantly, your life expectancy improves as you age. Once a man reaches 79, their life expectancy rises: to about 88, or nine more years. Fortunately, your death keeps on moving ahead of you and reaching the life expectancy you had at birth does not mean you are about to shift off this mortal coil. An average man reaching their 98th birthday can expect to live beyond 100.

The Health Foundation estimated a mean-average of 10 years of life lost for every Covid-19 death, with a similar figure for the US, and this holds even when allowing for pre-existing health conditions. So Covid-19 fatalities were not at death’s door.

Get Covid-19 and live longer? Sadly not.

• David Spiegelhalter is chair of the Winton Centre for Risk and Evidence Communication at Cambridge. Anthony Masters is statistical ambassador for the Royal Statistical Society