For months, scientists have been poring over data about cases and deaths to understand why it is that COVID-19 manifests itself in different ways around the globe, with certain factors such as the age of the population repeatedly popping up as among the most significant determinants. Now, one of the largest studies conducted of COVID-19 infection in the US has found that obesity of patients was the single biggest factor, after age, in whether those with COVID-19 had to be admitted to a hospital.