Ebola experimental vaccine first large-scale trial is 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 immunize 30,000 volunteers, including front-line health workers.
More than 8,500 people have died in the Ebola outbreak, the vast majority in Guinea, Liberia and Sierra Leone.
The trial beginning on February 2 will involve injecting a small amount of the strain of the Ebola virus into 12 volunteers in order to trick the body into producing an immune response.
However, it is not yet clear whether this will really offer protection against the disease.
Community nurses are being trained in how to monitor volunteers in the months after they have had their injections.
In the meantime, parts of the largest Ebola treatment centre in the world, on the edge of Monrovia, are being knocked down.
The number of Ebola cases in Liberia has been steadily decreasing – in recent months, there have only been five confirmed cases across the country.
The World Health Organization (WHO) says the epidemic has entered a “second phase” with the focus shifting to ending the epidemic.
The survival rate of the current Ebola outbreak is around 40%.