The slum-dwellers of Monrovia's Peace Island, refugees of civil war who found themselves suddenly overwhelmed and outmaneuvered by the deadly Ebola epidemic, are accustomed to life under siege.

Yet with Liberia emerging from the worst outbreak in history a year to the day since Ebola was first identified in West Africa, they are facing a deadlier threat - measles.

Experts say Liberia and its neighbors Guinea and Sierra Leone are ripe for an outbreak that could infect hundreds of thousands, dwarfing the carnage wrought by Ebola.