The World Health Organization declared an end to the deadliest Ebola outbreak ever on Thursday after no new cases emerged in Liberia, though health officials warn that it will be several more months before the world is considered free of the disease that claimed more than 11,300 lives over two years. Thursday's success comes after a harrowing toll: Nearly 23,000 children lost at least one parent or caregiver to the disease. Some 17,000 survivors are trying to resume their lives though many battle mysterious, lingering side effects. Liberia, which along with Sierra Leone and Guinea was an epicenter of the latest outbreak, was first declared free of the disease last May, but new cases emerged two times—forcing officials there to restart the clock. (A country is considered free of the disease when it has passed two incubation periods of 21 days without any more cases.)
Studies continue to uncover new information about how long Ebola can last in bodily fluids; it is now known that Ebola is present in the semen of some male survivors up to a year later. "While this is an important milestone ... we have to say that the job is still not done," said Rick Brennan, WHO director of emergency risk assessment and humanitarian response, at a news conference in Geneva. "That's because there is still ongoing risk of re-emergence of the disease because of persistence of the virus in a proportion of survivors." The most recent flare-up in Liberia confounded scientists as it was not initially clear where the new cases had come from. WHO now says those cases "are likely the result of the virus persisting in survivors even after recovery."