As of 21 September, the estimated cumulative number of confirmed Ebola virus disease (EVD) cases reported by WHO in the three most affected countries (Guinea, Liberia, and Sierra Leone) is 6,242, including 2,909 deaths. The ‘hidden caseload’, however, is unprecedentedly large, and these figures are believed to include only a fraction of all cases in this rapidly spreading epidemic.

According to a WHO projection, the aggregate caseload of EVD could exceed 20,000 by early November. Other agencies project the possibility of more than ten times as many cases, use different assumptions such as transmission to other countries, and evolution of the virus towards easier transmission between people.

The humanitarian community is already overwhelmed with the management of the epidemic and is greatly challenged in facing all the implications of this unprecedented and complex regional crisis. The current outbreak in West Africa is by far the largest ever recorded, and already numbers more cases than all past Ebola epidemics combined. 26 million people are estimated to live in the three most-affected countries. The epidemic started in Guinea in December 2013 but was only identified in March, and spread to Liberia, Sierra Leone, Senegal and Nigeria.