Ebola kills half of the people who get it. China's last worrying viral outbreak, SARS, killed 10 percent.
The new coronavirus that originated in the Chinese city of Wuhan appears far less fatal, with about 2 percent of all confirmed cases dying. For many, the illness is about as serious as a cold or the flu.
That seems like good news, but it is exactly what worries the scientists and public health experts who study infectious diseases ranging from the terrifying to the mundane.