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

Differences in testing regimes are a plausible mechanism driving the different detected age structures of cases [3, 10, 11] . This is consistent with our finding that differences between countries with extensive early testing of contacts to known cases (South Korea, Germany) are largely driven by differences in fatality and not by differences in the age distribution, suggesting that those countries might be more successful at catching the mild and asymptomatic cases among the younger population groups. However, it is also plausible that the extensive testing itself in these countries prevented undetected community spread to older population groups. Moreover, the data included in our analysis is also based on extensive testing for Italy and to a lesser extent for Spain, as these countries ramped up testing as the epidemic spread, making test numbers alone an unlikely explanation for the different age structure of detected cases.