Scientists are still trying to determine how the coronavirus that’s triggered a global health emergency spreads. Pinpointing where, when and how the pneumonia-causing virus transmits is key to formulating the most effective ways to protect people and stop the epidemic. In the absence of detailed, rigorously gathered and validated data, the current understanding about how the virus that causes Covid-19 spreads is largely based on what is known about similar coronaviruses. Doctors in China have in