What we know about the new coronavirus outbreak and how to respond

China by far is bearing the biggest burden of the new coronavirus outbreak - only about 100 cases have been reported outside the country. But on Thursday, the World Health Organization declared it a public health emergency of international concern, while at the same time recommending countries not limit trade and travel to China. Michael Mina, an infectious disease specialist at Harvard, explains what's known at this point about this disease and the best ways to respond.