"NB: Case fatality rates are inherently susceptible to certain biases. In diseases where there are asymptomatic or mild cases, there may a significant under-diagnosis of the disease relative to its true numbers in the population. In such cases, a case fatality rate would overestimate how lethal a disease is. In diseases where there can be a long period before death, if the time period given is too short, the case fatality rate may underestimate how lethal the disease is."