With cases declining in the United States and Europe, Nature examines scenarios of how the outbreak might play out.

On 29 April, a person in Nigeria developed an unusual rash and then travelled to the United Kingdom —carrying monkeypox with them. Since then, the virus has reached more than 70,000 people in over 100 countries. That has surprised health-care specialists around the world, because the sustained spread doesn’t resemble the sporadic pattern of previous monkeypox outbreaks in people, caused by a virus that lives in animals in Africa.

Almost six months after the virus started to spread, however, vaccination efforts and behavioural changes seem to be containing the current strain — at least in the United States and Europe (see ‘Monkeypox cases’). But the situation could still play out in several ways, say researchers. At best, the outbreak might fizzle out over the next few months or years. At worst, the virus could become endemic outside Africa by reaching new animal reservoirs, making it nearly impossible to eradicate. “There are so many factors at play that are working in opposing directions,” says Jessica Justman, an infectious-disease physician at Columbia University in New York City.

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