The current outbreak of Ebola virus disease is by far the biggest on record in terms of numbers of people affected and geographical spread. It is also the first time the disease has spread through a large urban environment. Since it began in Guinea in December 2013, it has spread to Liberia, Nigeria and Sierra Leone. As of 26 August 2014, there were 3,069 cases and 1,552 deaths.
No vaccine is currently approved to prevent infection, and the majority of people who succumb to disease will die. Local healthcare workers and international organisations are struggling to contain the disease while pharmaceutical companies scramble to push experimental vaccines through clinical testing.