note 1: The Nigeria Centre for Disease Control (NCDC) is reporting yellow fever outbreaks in multiple states (Bauchi, Benue, Delta, Ebonyi, and Enugu). Unless vaccinated, travelers should not visit these areas. Yellow fever is caused by a virus transmitted through bites of infected mosquitoes. Travelers to Nigeria should take steps to prevent yellow fever by getting vaccinated at least 10 days before travel and taking steps to prevent mosquito bites. Map courtesy of CDC.