Monkeypox has caught much of the world by surprise. But to Anne Rimoin, the warning signs have been obvious for years.

“What we’re seeing makes perfect sense,” says Dr. Rimoin, a professor of epidemiology at the University of California, Los Angeles’s school of public health.

Over decades, a confluence of factors – including declining population immunity, environmental degradation and growing international travel – has set the stage for an opportunity for monkeypox to leap beyond the African countries where it is usually found, she says.

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All it took was for the virus to be imported to the right place at the right time to spark the outbreak now occurring in parts of the globe that rarely or never saw the disease before, she says. “It seems to just have been an unfortunate roll of the dice.”