S EVENTEEN MONTHS into the covid-19 pandemic, plenty of questions about the catastrophe remain unanswered. It is still unclear how SARS-CoV-2 originated, for instance. Another puzzle is why some areas have had less destructive epidemics than others. Why has Florida had fewer deaths per person from covid-19 than the American average, even though restrictions there have been looser for longer? But researchers are getting closer to the “magic” variable: the factor that does most to explain variance in deaths from the virus. It turns out that this has little to do with health measures, climate or geography. Instead it relates to economics.
The huge literature on the determinants of covid-19 infections and deaths finds that many widely assumed relationships do not always hold in the real world. Everyone knows that the old are most at risk; but Japan, where 28% of people are over the age of 65 compared with 9% globally, has seen remarkably few deaths so far. Some studies suggest that places that had bad flu seasons before the pandemic suffered less since; but other researchers have called that conclusion into question. There is no consistent correlation between the toughness of lockdowns and cases or deaths.
Faced with these surprising results, a hunt has begun that is as morbid as it is nerdy. Wonks are searching for less obvious variables that do more to explain variation in deaths from covid-19. And so far the most powerful of them all is inequality—usually measured as the Gini coefficient of income, where zero represents perfect equality and one represents perfect inequality.