Testing has begun on humans for an experimental vaccine against the deadly Ebola virus, US researchers have said.
Ebola is one of the world's most lethal viruses
The National Institute of Allergy and Infectious Diseases is administering the vaccine to 27 volunteers.
In August, the institute said the same vaccine had worked to protect monkeys from the virus in a single shot.
The virus for one of the world's most lethal diseases originated in Africa and the US has expressed fears that it could be used as a biological weapon.
The vaccine uses pieces of DNA from the virus to prime the immune system; it is similar to other trial vaccines that may be used to control malaria, Aids and various strains of hepatitis.
As there is no known cure for the disease, preventing the spread of the virus is key to containing outbreaks.
"An effective Ebola vaccine not only would provide a life-saving advance in countries where the disease occurs naturally, it also would provide a medical tool to discourage the use of Ebola virus as an agent of bio-terrorism," Niaid Director Anthony Fauci said in a statement.
Ebola spreads easily from person to person through direct contact with bodily fluids and causes illness quickly - leading to internal bleeding and shock.
It kills 70% to 90% of the people it infects and, at present, there is no known cure.
It is named after a river in Zaire - now the Democratic Republic of Congo - where the virus was first discovered in 1976.
A recent outbreak of the disease in neighbouring Congo Brazzaville this month killed 11 people, according to reports.
Sporadic outbreaks in both countries and in Sudan have killed hundreds of people.