Before revision: By fitting a compartment ODE model for Covid-19 propagation to cumulative case and death data for US states and European countries, we find that the case mortality rate seems to have decreased by at least 80 percent in most of the US  and at least 90 percent in most of Europe. These are much larger and faster changes than reported in empirical studies, such as the 18 percent decrease in morality found for the New York City hospital system from March to August 2020 1 . Our reported decreases surprisingly do not have strong correlations to other model parameters (such as contact rate) or other standard state/national metrics such as  population density, GDP, and median age.
After revision: By fitting a compartment ODE model for Covid-19 propagation to cumulative case and death data for US states and European countries, we find that the case mortality rate seems to have decreased by at least 80 percent in most of the US and at least 90 percent in most European countries. These drops are much larger and faster changes than reported in empirical studies, such as the 18 percent decrease in morality found for the New York City hospital system from March to August 2020 1 . Our reported decreases surprisingly do not have strong correlations to other model parameters (such as contact rate) or other standard state/national metrics such as population density, GDP, and median age.