Infection fatality ratio and case fatality ratio of COVID-19

Luo, Guangze; Zhang, Xingyue; Zheng, Hua; He, Daihai

Infection fatality ratio (IFR) is the risk of death per infection and is one of the most important epidemiological parameters. For COVID-19, enormous efforts have been undertaken to estimate the IFR. Here, we discuss the pros and cons of several approaches and emphasize that the frequently used approach using serological survey result as the denominator and the number of confirmed deaths as the numerator will underestimate the true IFR. The most typical examples are South Africa and Peru (before official correction), wherein the confirmed deaths are only one third of the excess deaths. Our argument is that RT-PCR-based case fatality ratio (CFR) is a reliable indicator of the lethality of the COVID-19 in locations where testing is extensive. An accurate IFR is crucial for policy making and public-risk perception.