10 questions about the Covid-19 coronavirus outbreak, answered

The coronavirus outbreak, which began in China, keeps evolving at a dizzying speed. With the global case toll rising steeply (reaching over 125,000 on March 11), face masks flying off store shelves, borders around the world closing, and meetings, cruise itineraries, and the global economy upended by the virus, it’s no wonder questions and fears are swirling about Covid-19, as the disease is known.

On March 11, the WHO declared the outbreak a pandemic, a new disease that has spread around the world. Many countries have seen reported cases of...