The World Health Organization declared Nigeria, Africa’s most populous nation, officially free of Ebola infections yesterday, 20th October, 2014, calling the outcome the triumphal result of “world-class epidemiological detective work.” The announcement came 42 days after the last reported infection inNigeria’s outbreak, twice the maximum incubation period for the Ebola virus. The Nigerian response was upheld and praised by the W.H.O. as an example of the measures other countries can take to halt the spread of the epidemic, which is concentrated in three West African countries: Guinea, Liberia and Sierra Leone. “This is a spectacular success story that shows that Ebola can be contained,” the W.H.O. said in a report on its website. But it also expressed caution that Nigeria cannot relax its defenses against the deadly virus. More than 9,000 people have become infected in the epidemic, over 4,500 people have died, and the number of infections is still doubling every month, the W.H.O. has ...