The clinical trial of an Ebola vaccine in Switzerland has been interrupted after some patients complained of joint pains in their hands and feet.The trial was stopped one week early in all 59 volunteers "as a measure of precaution", the University of Geneva Hospital said.
The vaccine being tested is one developed by NewLink, and recently bought by Merck.
There is currently no vaccine licensed for use to protect against Ebola.
Two vaccines are currently being tested in humans in a number of countries.
The side-effects in the Geneva trial were experienced by four volunteers.
The hospital said human safety trials would resume on 5 January in up to 15 volunteers after checks had taken place to ensure the joint pain symptoms were "benign and temporary".
"They are all fine and being monitored regularly by the medical team leading the study," the hospital said.
Four trials of another Ebola vaccine developed by GlaxoSmithKline, in collaboration with the United States National Institute of Allergy and Infectious Diseases, are also underway.