The first large-scale trials of two experimental vaccines against Ebola have begun in Liberia. The potentially preventative medicines were 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, the vast majority in Guinea, Liberia and Sierra Leone.
The total number of reported cases is more than 22,000. In Liberia alone, more than 3,600 people have died from the disease. But the number of Ebola cases in Liberia has been steadily decreasing, with only four confirmed cases in the week leading up to 25 January.
According to the World Health Organization (WHO), the epidemic has entered a "second phase" with the focus shifting to ending the epidemic. The trial, which began on Monday, involves injecting 12 volunteers with a vaccine that contains a small, harmless fragment of the Ebola virus.
The aim is to trick the body into producing an immune response. More volunteers will be immunised as the trial progresses. However, it is not yet clear whether the trial vaccines will offer protection against the disease.
Vaccines train the immune systems of healthy people to fight off any future infection. They often contain a live but weakened version of the virus.
The trials are testing two vaccines created by two different drug companies who are hoping that the international community will eventually seek to stockpile large quantities of a working vaccine. The first man to receive the vaccine was a middle-aged Liberian.
The senior Liberian scientist involved in the trials, Stephen Kennedy.
"There is no danger because the piece of the Zaire strain that has been put into the vaccine is a weak strain and it cannot and will not cause Ebola, so it is impossible that any one of the volunteers will contract Ebola from the vaccine," Mr Kennedy said.
The scientists are well aware of how important the support of local people will be if this trial is to work. Community nurses are being trained in how to monitor volunteers in the months after they have their injections.
Parts of the largest Ebola treatment centre in the world, on the edge of Monrovia, are being knocked down, our correspondent says.
Survival rate for the current outbreak is around 40%.
The scale of the outbreak has sparked a race to find a cure for the disease, with many vaccines and drugs being fast-tracked for human testing.
Safety trials for potential vaccines have taken place in the UK and in Switzerland and two potential drugs have been tested at Ebola treatment facilities run by medical charity Medecins Sans Frontieres.
Doctors have also been trialling serum therapy, a treatment made from the blood of Ebola survivors who have recovered.
Ebola virus disease (EVD)
- Symptoms include high fever, bleeding and central nervous system damage
- Spread by body fluids, such as blood and saliva
- Fatality rate can reach 90% - but current outbreak has mortality rate of between 54% and 62%
- Incubation period is two to 21 days
- No proven vaccine or cure
- Supportive care such as rehydrating patients who have diarrhoea and vomiting can help recovery
- Fruit bats, a delicacy for some West Africans, are considered to be virus's natural host