We have seen varying estimates of the case fatality rate from Covid-19 (Coronavirus) infection. The case fatality rate is the percentage (or proportion) of patients with a disease who die. We should be cautious about accepting the estimates that have been published in medical journals as valid because many people will have undiagnosed infections. This is particularly likely in children, who often have mild symptoms (or no symptoms) when they contract a viral infection. Hence, the reported case fatality rates we have seen published in medical journals will overestimate the true death rate. As testing for Covd-19 infection becomes more widespread, we will get better estimates of the true infection rate in the population from the virus, and hence better estimates of the complication rate and death rate from the illness. In England, the new testing programme in people with respiratory tract infections announced by Public Health England will provide some of ths information.