As public health officials try to gauge the threat posed by a new virus that emerged in China, they are trying to answer a lot of key questions. One of them is this: How easy is it for the virus to spread?
Is the virus, known as 2019-nCov, mostly jumping from some animal source to people, with limited ability to transmit among humans? Or has it acquired the skill to spread easily from person to person?
Here’s a video explaining the difference between limited and efficient human-to-human spread and why it matters.