The Ebola virus that has killed more than 10,000 people in west Africa wrought a massive and costly international response. Yet more than a year after the first case was detected, Ebola has still not been eliminated in Sierra Leone, Guinea or Liberia. On the sidelines of an Institute of Medicine conference focused on the epidemic, Keiji Fukuda, the assistant director-general for health security at the World Health Organization, spoke with Scientific American’s Dina Fine Maron about what has most surprised him and will be seared into his memory for years to come.