Developing a vaccine usually takes time and is expensive, the WHO said.
"Even in best conditions and with the huge effort of many involved, a significant number of doses will not be available until the first quarter of 2015," the organisation said in a statement.
"The aim is to complete, in a few months, the work that usually takes two to four years, without compromising international standards for safety and effectiveness," the WHO said in a statement issued Wednesday.
The first of the two vaccines, cAd3-ZEBOV, is under development by GlaxoSmithKline in collaboration with the US National Institute of Allergies and Infectious Diseases.
The second one is rVSV-ZEBOV, and was developed by the Public Health Agency of Canada, although the marketing license belongs to US company NewLink Genetics.
Over the past six months, Ebola has infected 6,553 people and killed 3,100 in Liberia, Sierra Leone, Guinea and Nigeria. The worst outbreak since the virus was discovered in 1976 in what is now the Democratic Republic of the Congo.