A trial of NewLink Genetics Corp.'s experimental Ebola vaccine in Geneva, Switzerland, will be suspended after four cases of mild joint pain in the hands and feet of healthy volunteers.

Vaccination will resume Jan. 5, allowing time for researchers to gather more information and share it with other teams that are testing the shot, according to a statement from University Hospitals of Geneva, which is overseeing the trial.

Merck & Co. agreed last month to buy the rights to the vaccine and work with Ames, Iowa-based NewLink to develop it. Merck has operations in Montgomery County.

The mild joint pain was an unexpected side effect that occurred 10 to 15 days after the injection. Since Nov. 10, 59 people have been given the shot in Geneva in the first human trials of the vaccine, which is known as VSV-ZEBOV. Initial results show it's well-tolerated, according to the statement.

"Several investigations have been launched to ensure that the symptoms which have been identified are benign and transient," the hospital group said. "In the context of clinical trials, the safety of volunteers is always a priority."

Jack Henneman, the company's chief financial officer, declined to comment when contacted by phone.

Some volunteers experienced fever or muscle pain, side effects that they had been told to expect, the hospitals said. The vaccine also is being tested in Canada, the United States, Germany, and Gabon, where no symptoms of inflammation have been seen.

The Geneva trial is part of a race by drug companies and public health officials to develop a vaccine against the viral infection that has affected almost 18,000 people and killed almost 6,400, mostly in Sierra Leone, Liberia, and Guinea. Tests are underway of a shot being developed by GlaxoSmithKline Plc, and Johnson & Johnson plans to begin a trial of another vaccination.

Researchers had already planned to pause the Geneva trial the week of Dec. 22, a few days before Christmas, and resume it Jan. 5. So the suspension, with no injections next week, amounts to an extra week's break. Joint pain after infection or vaccination is common, according to the statement. It happens, for example, in one out of five vaccinations against rubella.

"This is a well-documented phenomenon which does not worry specialists," the hospitals said. "However, it deserves to be carefully studied in order to update the information which is provided to the volunteers. The temporary interruption of a clinical trial is a standard precautionary measure in such cases."

Glaxo reiterated that an assessment last month showed that its vaccine produced responses in volunteers and didn't raise safety concerns.