Contact tracing is improving. Treatments may be months away. Here’s what could determine whether a fast-expanding outbreak can be slowed down.

Aid agencies are racing to help health workers in the Democratic Republic of Congo. The virus is known to have killed at least 140 people, but the true toll may be far higher.

At once, Mahmood Mamdani’s fame was eclipsed by his son’s. At the same time, the election of Zohran Mamdani has attracted new interest in his father’s work.