A clinical trial of a possible Ebola vaccine had been halted after four patients in the trial being conducted in Geneva, Switzerland, complained of pain in their joints, researchers say.

The trial of the Merck-NewLink Ebola vaccine has been stopped temporarily as a precautionary measure, the University of Geneva Hospital announced.

"[The patients] are all fine and being monitored regularly by the medical team leading the study," the hospital said in a statement.

Of the 59 volunteers in the trial that began Nov. 10, only the four complained of pains in their hands and feet, hospital researchers said.

The trial is expected to resume on Jan. 5 with as many as 15 volunteers following an analysis to ensure the symptoms of joint pain were "benign and temporary," they said.

"The Geneva team has decided to allow time to understand what is happening. This precaution of momentarily suspending the trial is usual and classic in all clinical trials," the trial team said.

There is pressure to develop an Ebola vaccine following the worst outbreak of the virus disease ever witnessed which has killed more than 6,000 people in countries of West Africa.

In another trial of a GlaxoSmithKline Ebola vaccine with 120 volunteers being conducted at the University of Lausanne Hospital, safety data gathered to date has been acceptable, the university said.

The first definitive results of that trial, showing whether it can provide immunity against the Ebola virus, could be available by the end of this month, it said.

"The safety data looked satisfactory so far," said GSK trial leader Blaise Genton. "General symptoms such as fever might be slightly more frequent, though no serious adverse event has been observed so far."

The Merck-NewLink vaccine is also undergoing trials in the United States, Canada and Germany and in Africa in Gabon.

"These centers have not observed symptoms of inflammation in their volunteers to date," the Geneva team said.

The Merck-NewLink trial is the first of three phases of clinical trials normally required to obtain regulatory approval for a new drug.

The temporary halt to the Geneva trial would provide an opportunity to gauge how serious or widespread the reported joint pain problem might be, but it should be able to go on as planned, says Marie-Paule Kieny, vaccine expert at the World Health Organization.

"It's not a setback, not at all," Kieny said at a WHO briefing on the vaccine efforts.