The Interim Case Fatality Rate (ICFR) of the COVID-19 Pandemic for Europe and the United States from March 1, 2020 to August 15, 2021. Does the ICFR Regress to the Final CFR?

Objective: The true case fatality rate (CFR) of a disease outbreak can only be ascertained after all cases and deaths have been tabulated at the end of the epidemic. We define a metric, the interim case fatality rate (ICFR) which is the incremental change in the ratio of cases to deaths. To examine longitudinal changes in the ICFR of the COVID-19 pandemic and to evaluate the likelihood that the ICFR can predict the final CFR.

Methods: Publicly available databases were used to gather data on the number of cases and deaths in Europe and the United States (USA). These data were gathered over the period from Mar.1, 2020 to Aug. 15, 2021, on four regions of the USA and four regions of Europe on a bi-weekly basis. Statistical methods were utilized to evaluate changes over the final month of the study (July 15, 2021 to August 15, 2021). Stability of the ICFR was based on acceptance of the null hypothesis that no significant difference (p>0.05) was observed over that period.

Results: In all regions studied, the early months of the pandemic were marked by very high ICFRs. By late 2020, these began to stabilize at levels well below 5%. During the final month of the study, only one (Northeast USA) of the eight regions evaluated showed a statistically significant difference in ICFR. Mean ICFR projections, based on weighted values of cases are 1.8% (95% CI: 1.2% to 2.3%) for the USA and 2.1% (95% CI: 1.5% 2.7% for Europe.

Conclusion: After an early peak, very little change was observed in the ICFR, and by summer 2021, the rates had stabilized. Weighted ICFR for all regions may well reflect the final ICFR.