This wide range doesn’t get us closer to a “true” mortality rate. Instead, it suggests something else that’s important: the virus’s lethality depends on a whole host of factors that are extrinsic to the virus itself. Put another way, even if we could count every single infection and every single death from the virus, without missing anyone, the risk of dying from the virus would still vary from country to country, city to city and person to person. We know that the virus is more dangerous in the elderly, for example, so we expect mortality to be higher in countries with older populations, like Italy. We know that the virus is more dangerous if you have comorbidities like hypertension or diabetes, so we might expect mortality to be higher in countries with more of these diseases, as in the U.S.
Hospital capacity also influences the risk of dying from the virus, because the quality of medical care suffers when a hospital is overwhelmed. Capacity varies from country to country: Germany has eight hospital beds per thousand people, for instance, but the U.S. has less than three. Mortality rates can evolve over time, too. According to the WHO, mortality decreased in Wuhan because hospitals were inundated early on and then increased their capacity later in the outbreak.
So, the mortality rate, instead of being a fixed number that distills the true essence of the virus’s danger, is actually a protean, organic, fluid metric.