Changing case fatality risk for COVID-19 over time in selected European countries

ObjectivesTo illustrate the development of the case fatality risk (CFR) for COVID-19 over time using different assumptions for calculating the CFR. DesignObservational study. Setting Selected European countries, 28 January to October 29 2020. ParticipantsLaboratory-confirmed COVID-19 cases and deaths due to COVID-19 Main outcome measurecase fatality risk (CFR) ResultsWe show that the CFR has considerably decreased over time. This seems to be driven not only by increased testing but also by a reduced CFR among cases older than 60 years. Our data also confirm a significantly higher fatality risk for men than for women. The decline in the CFR is even more pronounced when only cases and deaths occurring in a specified time window are considered. This alternative estimation method has the advantage that early data where the bias due to the incomplete ascertainment of cases was arguably largest do not affect CFR estimates later on. We find similar results for other European countries. ConclusionCFR estimates vary considerably depending on the underlying assumptions concerning their calculation. Reliable CFR estimates should not be based on cumulative numbers from the beginning of the pandemic but rather be based on more recent data only.