Three doctors in Liberia with Ebola who started taking an experimental drug last Thursday are showing remarkable signs of improvement, a minister says.
ZMapp was first given earlier this month to two US aid workers, who were flown home for treatment from Liberia.
Ebola has no cure but the World Health Organisation has ruled that untested drugs can be used in light of the scale of outbreak in West Africa.
Since the beginning of the year, 1,229 people have died of the virus.
It is transmitted by direct contact with the body fluids of an infected person. Initial flu-like symptoms can lead to external haemorrhaging from areas such as eyes and gums, and internal bleeding which can cause organ failure.
The outbreak began in Guinea and has since spread to Liberia, Sierra Leone and Nigeria.
Health officials in Guinea say the country has suffered a setback in its fight against the epidemic, seeing a resurgence of cases in the town of Macenta.
The BBC’s Alhassan Sillah in Guinea says the town had not had any cases for two months, and the authorities had dismantled all Ebola facilities in that area.
The health authorities believe that Guineans returning from neighbouring Liberia are carrying the virus.
In Liberia, Information Minister Lewis Brown said the government only received a small number of ZMapp doses and gave them to one Nigerian and two Liberian doctors who had caught Ebola whilst helping save the lives of other victims of the virus.
Two US missionaries who received doses of the medicine are also reportedly recovering, but a 75-year-old Spanish priest who contracted Ebola in Liberia died in Spain last week despite being given the drug.
The US pharmaceutical company that makes the drug says it has for now run out of it, so the only way to stop the current outbreak is to isolate the victims and those who have come into contact with them.
Brown also said 17 suspected Ebola patients who went missing after a health centre in the capital was attacked have been found.