The deadliest Ebola outbreak ever is finally slowing in Liberia, the worst-hit country, but still wreaking havoc in two neighboring west African states amid warnings of thousands of unreported deaths.

As the initially lackluster global response to the crisis centered in Liberia and adjoining Sierra Leone and Guinea gathered some pace following repeated and impassioned appeals from top UN officials and world leaders, the good news from Liberia was tempered by warnings that the global toll is likely vastly underestimated.

The outbreak is officially thought to have claimed 4,960 lives and infected 13,042 people, according to the latest data issued by the World Health Organization. But that could be the tip of the iceberg, an official at the UN health agency said.