On the dramatic change in COVID-19 mortality rate: Modeled and examined for Europe and the US

Our compartment model (Khan et al.) [1] shows that the COVID-19 case mortality rate decreased by at least 80% in most of the US states and at least 90% in most European countries. These drops are much larger and faster than those previously reported and surprisingly do not correlate well with our model parameters (such as the contact rate or testing rate) or state/national metrics such as the population density, GDP, and median age. Surprisingly, these changes mostly occurred between mid-April and mid-June – at a time when lockdown relaxations in many states and countries caused surges of new cases. Plausible causes for this drop are discussed, such as improvements in treatments, face mask wearing, a new virus strain, and age demographics of infected patients, but none alone support such large decreases.

MSC Codes 92-10