I’m regularly asked to explain how it is that the severity and mortality of the current outbreak are tied to so many factors, all of which seemingly have high explanatory power on their own. Whether it’s diabetes, COPD, obesity, air pollution, age, or anything else, they all, according to various studies, explain the differential risk faced by individuals.
Here is an answer I gave recently, arguing that there are (at least) two ways to look at this, one more epidemiological, and one more holistic and almost philosophical:
- There is obviously multicollinearity here, with many of these putative explanations captured, to a greater or lesser degree, by other explanations. An obesogenic environment, for example, is closely tied to weight, air pollution, gender, age, and diabetes. Epidemiological explanations are, in all but the most trivial cases, over-determined: there are more causes than consequences.
- If everything explains differential Covid-19 severity, then it might arguably be characterized as a disease of modernity, like depression. Its spread and mortality then become merely the clinical manifestations of the environment in which we live. Trying to parse out a single risk factor or causal chain for increased severity or mortality then becomes somewhat futile, like parsing a central causal factor for depression, beyond modernity, of course.