By Andrew Morse 

ZURICH--Tests of two Ebola vaccines currently under development could begin in West Africa as early as the end of the month, a senior World Health Organization official said Friday.

Dr. Marie-Paule Kieny, the WHO assistant director general for health systems and innovation, said at a news conference following a meeting of experts in Geneva that tests in Liberia could begin before the end of January, while tests in Sierra Leone and Guinea, two other West African countries that have been hit hard by the disease, could begin in the following month.

One of the two vaccines is being developed by GlaxoSmithKline PLC, while the other has been licensed by Merck & Co. Other vaccines, including ones in Russia and China, are also under development, Dr. Kieny said.

"At this time last year I would have said the cupboard was empty," Dr. Kieny said. "But now the cupboard is clearly filling up rapidly."

Testing of the Merck vaccine, which was licensed from NewLink Genetics Corp., was briefly stopped at a hospital in Geneva last month after several volunteers reported joint pain in their hands and feet. The hospital said last week that testing would resume at a new, lower dosage after the symptoms cleared up without treatment.

Dr. Kieny acknowledged the side effects but said they weren't "of sufficient concern to stop the development of this vaccine."

Currently no vaccines currently exist to protect against Ebola.

A total of 20,972 confirmed, suspected or probable cases of Ebola have been recorded so far in Liberia, Sierra Leone and Guinea, the three countries most affected by the current outbreak, according to WHO data released on Thursday. The disease has killed 8,259 people.

Write to Andrew Morse at andrew.morse@wsj.com

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