The first large-scale trials of an experimental vaccine against Ebola are due to begin in Liberia.
The potentially preventative medicine was taken under strict security to a secret location in the West African country.
Scientists aim to immunise 30,000 volunteers, including front-line health workers.
More than 8,500 people have died in the Ebola outbreak, most of whom are from Guinea, Liberia and Sierra Leone.
The total number of reported cases is more than 21,000. In Liberia alone, more than 3,600 people have died from the disease.
The trial beginning on Monday would involve injecting a small amount of the Ebola virus into volunteers in order to trick the body into producing an immune response.
The vaccine is still experimental and it is not clear whether it will definitely provide protection against Ebola.
Community nurses are being trained in how to monitor volunteers in the months after they have had their injections.
The number of Ebola cases in Liberia have been steadily decreasing. In recent months, there have only been five confirmed cases across the country.