China has ordered an unprecedented quarantine of more than 50 million people . It has closed schools and shut down live animal markets. Airports across the globe are screening passengers coming from the world’s most populous country. But three weeks after the new coronavirus emerged as a health crisis, experts can’t yet say whether these efforts will succeed at containing an infection that now threatens at least 15 countries. Some early signs are discouraging: Six countries, including China, have confirmed human-to-human transmission of the infection. Those include four cases in Germany connected to a single person — a worrisome sign for containment of the disease. Cases in China continue to multiply, and five million residents of Wuhan, where the virus originated, have left the […]