The World Health Organization has declared an end to the deadliest Ebola outbreak on record, reports the New York Times. The announcement comes after the countries hit hardest by the epidemic—Liberia, Sierra Leone, and Guinea—reported zero cases for 42 days, or two incubation periods. During its two thriving years, the epidemic killed 11,300 people and infected more than 28,500.

These countries aren’t out of the woods yet (when are African countries ever out of the woods?). W.H.O. General Director Margaret Chan said in a statement, “Our work is not done and vigilance is needed to prevent new outbreaks.” Flare-ups, like one that recently hit Liberia, are possible. The Times reports:

The immediate threat stems from persistence of the virus in body fluids, notably in the semen of male survivors, up to a year after they are cured of the disease and show no symptoms, said Rick Brennan, the W.H.O.’s director of emergency risk management, in Geneva.

Ten flare-ups had been reported across the three countries in the last nine months, four of them in Liberia and three each in Guinea and Sierra Leone, “and we are anticipating more,” Mr. Brennan said.

[Image via AP]