Monitoring trends and differences in COVID-19 case fatality rates using decomposition methods: Contributions of age structure and age-specific fatality

Christian Dudel; Tim Riffe; Enrique Acosta; Alyson A. van Raalte; Mikko Myrskyla

Examples of this discrepancy are shown in Figure 1 . As of March 24, 2020, Germany had a total of around 27 thousand confirmed infections and 114 deaths, resulting in a CFR of around 0.4%. Italy, on the other hand, up to the same day, had close to 64 thousand confirmed cases of infection, around 6 thousand deaths, and a CFR of 9.5%. On March 16, Italy had roughly the same number of cases as Germany on March 24, and a CFR of 7.7%. Thus, the outbreak in Italy is going along with a much higher CFR, and the CFR increased over time [2, 3] . Differences in the CFR could indicate that the risk of dying of COVID-19 among detected cases differs between countries or changes within a population over time. On the other hand, it could also imply compositional differences in the detected infections [1, 3] . Specifically, the risk of dying of COVID-19 is well-documented to increase with age. Thus, if the population of infected individuals is older in one country or time period than in another, the CFR will be higher, even if the age-specific risk of dying is the same.