The World Health Organization decided not to declare a global health emergency — yet. Several members thought it was “still too early,” the W.H.O. said in a statement.

The details: The virus has killed at least 18 and sickened more than 600. Here are maps of its spread. The victims are so far mostly older men, many of whom had previous health issues.

What’s next: The Lunar New Year holiday, when hundreds of millions travel across China, begins today. Epidemiologists fear it could make the outbreak harder to contain.