Will the Wuhan virus become a pandemic?

TWO THINGS explain why a new infectious disease is so alarming. One is that, at first, it spreads exponentially. As tens of cases become hundreds and hundreds become thousands, the mathematics run away with you, conjuring speculation about a health-care collapse, social and economic upheaval and a deadly pandemic. The other is profound uncertainty. Sparse data and conflicting reports mean that scientists cannot rule out the worst case—and that lets bad information thrive.

So it is with a new coronavirus, known as 2019-nCoV, which has struck in China. The number of reported cases grew from 282 on January 20th to almost 7,800 just nine days later. In that time four reported cases outside mainland China have multiplied to 105 in 19 territories. Doubt clouds fundamental properties of the disease, including how it is passed on and what share of infected people die. Amid the uncertainty, a simulation of a coronavirus outbreak by Johns Hopkins University in October, in which 65m people lost their lives, was put about as a prediction. It is not.