Abstract
BackgroundThe infection fatality rate (IFR) of the Coronavirus Disease 2019 (COVID-19) is one of the most discussed figures in the context of this pandemic. In contrast to the case fatality rate (CFR), the IFR depends on the total number of infected individuals – not just on the number of confirmed cases. In order to estimate the IFR, several seroprevalence studies have been or are currently conducted.MethodsUsing German COVID-19 surveillance data and age-group specific IFR estimates from multiple international studies, this work investigates time-dependent variations in effective IFR over the course of the pandemic. Three different methods for estimating (effective) IFRs are presented: (a) population-averaged IFRs based on the assumption that the infection risk is independent of age and time, (b) effective IFRs based on the assumption that the age distribution of confirmed cases approximately reflects the age distribution of infected individuals, and (c) effective IFRs accounting for age- and time-dependent dark figures of infections.ResultsEffective IFRs in Germany are estimated to vary over time, as the age distributions of confirmed cases and estimated infections are changing during the course of the pandemic. In particular during the first and second waves of infections in spring and autumn/winter 2020, there has been a pronounced shift in the age distribution of confirmed cases towards older age groups, resulting in larger effective IFR estimates. The temporary increase in effective IFR during the first wave is estimated to be smaller but still remains when adjusting for age- and time-dependent dark figures. A comparison of effective IFRs with observed CFRs indicates that a substantial fraction of the time-dependent variability in observed mortality can be explained by changes in the age distribution of infections. Furthermore, a vanishing gap between effective IFRs and observed CFRs is apparent after the first infection wave, while an increasing gap can be observed during the second wave.ConclusionsThe development of estimated effective IFR and observed CFR reflects the changing age distribution of infections over the course of the COVID-19 pandemic in Germany. Further research is warranted to obtain timely age-stratified IFR estimates, particularly in light of new variants of the virus.
Highlights
Introduction ofGerman tracing app (“Corona-Warn-App”).16 Jul 2020Specification of “hotspot strategy” with targeted local measures in affected districts.02 Nov 2020Lockdown “light”, including stricter contact restrictions and closures of restaurants and leisure facilities.16 Dec 2020Second lockdown, including closures of non-essential stores and switch to distance learning in schools.Note that, due to the federal structure of Germany, there have been specific differences in implemented measures between the 16 German federal states the virus to older age groups could be reduced after incidences reached more controllable levels
As the second wave of infections in Germany has been ongoing at the time of writing, it is too early for a conclusive evaluation of mitigation measures, including the “lockdown light” and the “second lockdown”; our results show that estimated effective infection fatality rate (IFR) have been continuously rising with increasing numbers of cases until December 2020
In this work we have focused on estimating the effective IFR based on the changing age distribution of infections; in practice many other factors may contribute to the variability in mortality of COVID-19, such as the distribution of different comorbidities as well as the sex distribution of infected individuals
Summary
Introduction ofGerman tracing app (“Corona-Warn-App”).16 Jul 2020 (week 29)Specification of “hotspot strategy” with targeted local measures in affected districts.02 Nov 2020 (week 45)Lockdown “light”, including stricter contact restrictions and closures of restaurants and leisure facilities.16 Dec 2020 (week 51)Second lockdown, including closures of non-essential stores and switch to distance learning in schools.Note that, due to the federal structure of Germany, there have been specific differences in implemented measures between the 16 German federal states (not listed here) the virus to older age groups could be reduced after incidences reached more controllable levels. During summer 2020, with relaxed mitigating measures still in place, such as the requirement of wearing masks in stores and public transport, incidences of COVID-19 remained relatively low. In this time, there was a young age distribution of cases, resulting in small estimated effective IFRs and a reduced disease burden for high-risk groups. As the second wave of infections in Germany has been ongoing at the time of writing, it is too early for a conclusive evaluation of mitigation measures, including the “lockdown light” and the “second lockdown” (see Table 2 and Fig. 1); our results show that estimated effective IFRs (and observed CFRs) have been continuously rising with increasing numbers of cases until December 2020. The two meta-analyses differ heavily regarding their results and conclusions, both observe a high heterogeneity in population-averaged IFR estimates among different studies and emphasize the importance of obtaining reliable age-stratified estimates
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