Key epidemiologic parameters of COVID-19

WHO is working with an international network of statisticians and mathematical modelers to estimate key epidemiologic parameters of COVID-19, such as the incubation period (the time between infection and symptom onset), case fatality ratio (CFR, the proportion of cases that die), and the serial interval (the time between symptom onset of a primary and secondary case). Preliminary estimates of median incubation period are 5-6 days (ranging from 0-14 days) and estimates for the serial interval range from 4.4 to 7.5 days. The confirmed case fatality ratio, or CFR, is the total number of deaths divided by the total number of confirmed cases at one point in time. Within China, the confirmed CFR, as reported by the Chinese Center for Disease Control and Prevention is 2.3%. This is based on 1023 deaths amongst 44,415 laboratory-confirmed cases as of 11 February. This CFR does not include the number of more mild infections that may be missed from current surveillance, which has largely focused on patients with pneumonia requiring hospitalization; nor does it account for the fact that recently confirmed cases may yet develop severe disease, and some may die. As the outbreak continues, the confirmed CFR may change. Outside of China, CFR estimates among confirmed cases reported is lower than reported from within China. However, it is too early to draw conclusions as to whether there are real differences in the CFR inside and outside of China. For more details, see Situation Report 30.