COVID-19 case fatality rate and infection fatality rate from 2020 to 2023: Nationwide analysis in Austria.

BACKGROUND

Comprehensive analyses of COVID-19 case fatality rates (CFRs) and infection fatality rates (IFRs) that span the entire pandemic are not yet available but critical to retrospectively evaluate the COVID-19 disease burden and its related public health policies. We used nationwide individual participant data from Austria, the continental country with the highest SARS-CoV-2 testing rate per capita, to calculate COVID-19 CFR and estimate IFR covering the entire pandemic.

METHODS

This retrospective observational study included all Austrian residents and covered the time from February 2020 to May 2023, examining CFRs overall, monthly, and during dominant SARS-CoV-2 variant periods. CFRs were calculated for the whole population and stratified according to immunization status (presence of previous vaccination and/or infection), age, gender and nursing home residency. We additionally estimated the IFRs based on estimations of undocumented infections using a test positivity model.

RESULTS

The overall CFR of 30-day COVID-19 mortality was 0.31 % but varied depending on month, with the highest being 5.9 % in April 2020 and the lowest 0.07 % in January 2022. The variant periods reflected this trend of decreasing CFR, with the highest for Wuhan-Hu-1 (2.05 %) and the lowest for BA.1 (0.08 %). Overall CFRs were particularly high in the group without any previous immunizing event (0.67 %), the elderly (85 + year group: 7.88 %) and in nursing home residents (7.92 %). Nursing home residents accounted for 30.82 % of all COVID-19 deaths while representing only 1.22 % of diagnosed infections. Total SARS-CoV-2 infections were estimated to be almost double than confirmed cases with a corresponding overall IFR of 0.16 %.

CONCLUSION

This estimation of nationwide CFR and IFR across the entirety of the SARS-CoV-2 pandemic gives crucial insights into the period-dependent variability of the severity of diagnosed COVID-19 cases and its risk factors. Our findings further underline the disproportionate severity of COVID-19 among the elderly and especially nursing home residents.