The preliminary results were published on Friday in the medical journal The Lancet. The trial of the VSV-ZEBOV vaccine began on 23 March 2015 in Guinea in West Africa, and researchers describe administering a single dose of the vaccine to over 7,500 infected people.
The researchers used a method called the "ring strategy," where they vaccinated people who had come into contact with an infected person. This is intended to form a protective ring, and prevent the virus from spreading.
If the vaccine proves effective in the long-term, it could potentially bring an end to an epidemic that has caused large-scale socio-economic impact, and led to the death of at least 11,261 people as of July 2015. The clinical trials are supported by several international organizations, including the World Health Organization, the Norwegian Institute of Public Health, Medecins san Frontieres (MSF), and the Wellcome Trust.
Though the first results are promising, researchers caution that further evidence is needed on the vaccine's ability to interrupt transmission, and to protect populations through what's known as "herd immunity." This is when so many people are vaccinated that they protect those who have not yet developed immunity against a particular disease.
Developing vaccines against infectious diseases takes time. According to a blog post by global medical non-profit the Wellcome Trust, it usually takes over two years to decide whether a vaccine is safe for people to use, or even effective at providing protection against diseases. The Wellcome Trust therefore created an Ebola Research Funding initiative in August 2014 in order to speed up the process of finding an effective vaccine. At that point, there were no Ebola vaccines that could be immediately tested in West Africa.
Before 26 July, half the individuals in the trial were being vaccinated three weeks after the discovery of an infected patient, while half were vaccinated immediately. This allowed the researchers to compare results between the two groups of vaccinated people. This has now been terminated so that people who are at immediate risk of infection can be vaccinated. Given the success of the preliminary findings, children will also now be included in the ongoing trial.