Population-Level Mortality Rates from Novel Coronavirus (COVID-19) in South Korea

Samir Soneji; Hiram Beltrán-Sánchez; JaeWon Yang; Caroline Mann

The first case of the novel coronavirus in South Korea occurred in late January 2020, approximately two months after the first case globally occurred in the Hubei province of China. 1 The number of cases quickly increased after an infected 61-year old woman attended religious services with over one thousand other people. 2 Approximately one month after this first case and three days after the first death, South Korean President Moon Jae-In raised the national alert level to its highest possible level and instituted voluntary lockdown of affected cities and provinces. 3 In addition to these precautionary measures, South Korea implemented widespread screening and has currently tested more people per capita than any other country. 4 Case fatality rates are the most common measure used to assess the mortality burden of COVID-19. These rates are computed as the ratio of deaths due to COVID-19 to the number of people infected by the disease. However, comparison of COVID-19 case fatality rates across countries and historic pandemics is problematic because the true number of cases may far exceed the reported number of cases (i.e., the denominator of the case fatality rate) in most countries due to a lack of testing. 5 Even in countries with widespread testing, the mortality burden of COVID-19 is more appropriately measured by age-specific mortality rates. In contrast to case fatality rates, mortality rates are computed by dividing deaths due to COVID-19 and the exposure measured in person-years lived (i.e., the entire population is at risk of infection and death from COVID-19). In addition, while case fatality rates provide a good assessment of the likelihood of death conditional on contracting the disease, mortality rates provide an overall risk of death for the entire population. These mortality rates can then be summarized into the age-standardized death rate (ASDR), which accounts for differences in the age distribution of populations and allows appropriate comparison across countries. The age distribution is an important factor because COVID-19 is more fatal among older adults and countries differ considerably in their proportion of older adults (e.g., 16% of the population of South Korea is aged ≥65 years compared to 12% in China and 23% in Italy). 6 We address this research gap by utilizing standard demographic and epidemiological principles to estimate the population-level mortality rate for COVID-19 in South Korea. We focus on South Korea because it was among the first countries to report a case of COVID-19 and make public its case distribution and case fatality rates by age. This paper makes three important contributions. First, we estimate population-level mortality rates from COVID-19 by age. Second, we also consider alternative scenarios in which the prevalence of COVID-19 increased and compare the mortality burden of the observed pandemic and these alternative scenarios with leading causes of death in South Korea. Finally, we make available easy-to-use software for public health researchers, government officials, and international health organizations to input case distributions by age, case fatality rates by age, and the total number of cases (either laboratory confirmed or alternative scenarios) to estimate the mortality burden of COVID-19 for other countries.