A case fatality ratio of an infectious disease measures the proportion of all individuals diagnosed with a disease who will die from that disease. For an emerging infectious disease, this ratio is thus a very important indicator not only of disease severity but also of its significance as a public health problem. For instance, WHO estimated a case fatality ratio of approximately 14–15% for severe acute respiratory syndrome (SARS) in 2003,1 and approximately 35% for Middle East respiratory syndrome (MERS) in 2012.

The ongoing pandemic of coronavirus disease 2019 (COVID-19) is caused by a virus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), belonging to a large family of coronaviruses that also includes SARS coronavirus (SARS-CoV) and MERS coronavirus (MERS-CoV). COVID-19 was first reported in December, 2019, in Wuhan, in the Hubei province of China, and spread very rapidly to all other prefectures in Hubei, as well as all other provinces, autonomous regions, municipalities, and special administrative regions of China, and more than 180 other countries and territories. As of March 21, 2020, there have been 292 142 confirmed cases of COVID-19 worldwide, with 12 784 deaths reported.