The world may have an effective vaccine against the Ebola virus, it has been announced.
The vaccine can even be used to protect people who have already been exposed to the virus, researchers reported.
The finding means the vaccine could be used for rapid containment of outbreaks.
The vaccine VSV-ZEBOV was tested on more than 7,500 people in the country of Guinea in a region hit by a new outbreak of the disease.
Researchers say the vaccine gave 100% protection within ten days of being administered.
The study required some of those at risk to wait 21 days for vaccination so the treatment could be evaluated.
Out of 2,000 adults who received immediate vaccination, nobody fell ill with the disease after a period of ten days. This compared with 16 people among those who did not receive the vaccine for three weeks.
The study involved 90 clusters of people allowing researchers to test the idea of "ring vaccination" – which seeks to create a protective circle after someone has fallen ill with the disease. This is done by vaccinating their contacts and their contacts.
The findings were published by The Lancet.
Researcher Dr Marie Paul Kieny, of the World Health Organisation, said: “Before the trial started, in most clusters there had been a series of Ebola cases over the weeks prior to randomisation.
"However, since the trial started, we have seen no new cases in vaccinated volunteers within ten days of vaccination, regardless of whether vaccination was immediate or delayed.”
She added: “This record-breaking work marks a turning point in the history of health research and development. We now know that the urgency of saving lives can accelerate research and development."
Fellow researcher Professor John-Arne Røttingen, from the University of Oslo, Norway, said the results were "encouraging."
He said: "Because the way that Ebola virus transmits has been shown to be consistent across countries and regions, we believe that these results are likely to be applicable to other regions of Guinea and to Sierra Leone and Liberia.
"But whether this candidate vaccine could become a licensed vaccine for widespread use against Ebola outbreaks is still uncertain, and further evidence is needed to evaluate the safety and efficacy of the vaccine before it is used outside of a clinical trial setting.”
Efficacy and effectiveness of an rVSV-vectored vaccine expressing Ebola surface glycoprotein: interim results from the Guinea ring vaccination cluster-randomised trial. Lancet 31 July 2015 [abstract]
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