Nigeria has been declared officially free of Ebola after six weeks with no new cases, the World Health Organization said.WHO representative Rui Gama Vaz, speaking in the capital Abuja, said it was a "spectacular success story". Nigeria won praise for its swift response after a Liberian diplomat brought the disease there in July. The outbreak has killed more than 4,500 people in West Africa, mostly in Liberia, Guinea, and Sierra Leone.