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.
Initial efforts to understand the behavior of the COVID-19 virus by researchers in Singapore suggest it is different from Severe Acute Respiratory Syndrome (SARS) and has more similarities with H1N1. Like influenza, COVID-19 is infectious when symptoms are mild, the researchers found. Because of this transmission mechanism, COVID-19, like influenza, can spread quite quickly, as people with mild symptoms may let their guard down.