How Many Life-Years Could Be Lost to Coronavirus Disease in the UK?
Considers the total number of life-years that could be lost to coronavirus disease in the UK, under different assumptions
The Imperial College report published on 16 March stated that there could be “hundreds of thousands of deaths” from coronavirus disease in the UK if no measures were taken to actively suppress the epidemic. (Note that one could have obtained a figure of about this size via a simple back-of-the-envelope calculation: 66 million people x 50% prevalence x 1% mortality = 330,000 deaths.)
However, it has been claimed (e.g., on Twitter and elsewhere) that most of these deaths will afflict people who would have only lived another year or two anyway. This claim appears to be based on the fact that the case fatality rate for coronavirus disease is much higher for people in their seventies and eighties than for people in younger age groups, and that it is below 1% for people younger than 50.
If most of the people who die from coronavirus disease would only have lived another year or two anyway, the epidemic is arguably less concerning than if most of them would have lived many more years. In other words, we are not concerned so much with the total number of deaths from coronavirus disease, but rather with the total number of life-years lost. (All else being equal, it is worse if someone who is 25 dies than if someone who is 85 dies, since the former has more years left to live than the latter.)
In order to investigate how many life-years could be lost to coronavirus disease in the UK, I took data on the age distribution of deaths from a report by the Italian National Institute of Health (n = 5,542). And I took the average conditional life expectancies for people in the corresponding age groups from the UK national life tables. (A weighted average was used, with male figures being assigned the weight ‘0.71’ and female figures being assigned the weight ‘0.29’, due to the fact that 71% of those who have died from coronavirus disease in Italy were male.)
To compute the expected life-years lost in each age group, the weighted average conditional life expectancy was multiplied by the expected number of deaths from coronavirus disease. I used a figure of 330,000 for total deaths from coronavirus disease (as per the calculation above). Hence the expected number of deaths in a particular age group was equal to 330,000 multiplied by the proportion of deaths from coronavirus disease in that age group. (I obtained the age distribution of deaths for the UK by combing the Italian age-specific mortality rates with the UK’s population age structure. My calculations can be found in this spreadsheet.)
My calculations yielded a figure of 3.7 million life-years lost, which is roughly eleven times higher than the figure one would obtain by assuming that everyone who dies from coronavirus disease would have only lived one more year of life. (In other words, individuals who die from coronavirus disease would have lived, on average, eleven years more.) However, this figure should be considered an upper-bound for one very important reason, namely that a large percentage of the people who have died from coronavirus disease in Italy had one or more comorbidities. (The most common comorbodities are given in Table 1 of the report.)
This means that the average conditional life expectancies I used almost certainly overstate the true life expectancies of people who are likely to die from coronavirus disease. (For example, although the average 55 year old male may live another 27.4 years, the average 55 year old male with hypertension and ischemic heart disease is likely to live somewhat fewer years.) Another way of saying this is that coronavirus disease appears to selectively target people whose life expectancy is lower than the average for their age group.
It is not clear (since I am not an expert, and do not know where to find the relevant data) by how much the average conditional life expectancies should be reduced to account for the selective targeting of people with pre-existing conditions. Dividing each of them by two would yield an overall figure half as big as the one given above, namely 1.9 million life-years lost. This is still almost six times higher the figure one would obtain by assuming that everyone who dies from coronavirus disease would have only lived one more year of life.
One major caveat to my analysis is that, in addition to many deaths, the coronavirus epidemic will cause a large number of people to get ill, some of whom will develop permanent debilitating conditions. A more comprehensive analysis would take this into account as well. Another caveat is that life expectancies are based on current age-specific death rates, so may over or underestimate the life trajectories that people alive today will actually experience. It is also worth mentioning that coronavirus disease has the potential to become endemic, in which case it would cause additional life-years to be lost in future years.
(For an interesting analysis of how the coronavirus epidemic might affect life expectancy in the US, see this blog post by Anatoly Karlin.)