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A breakthrough Ebola vaccine has proved 100 percent effective in a trial that took place in Guinea and has been called a "game changer" by the World Health Organisation (WHO).

Preliminary results from the trial of the VSV-EBOV vaccine, which was created by the Public Health Agency of Canada and developed by pharmaceutical company Merck, have been published in the Lancet. "This is an extremely promising development," said Margaret Chan, Director-General of the WHO. "The credit goes to the Guinean Government, the people living in the communities and our partners in this project. An effective vaccine will be another very important tool for both current and future Ebola outbreaks."


The results thus far have revealed that the the vaccine is 100 percent effective effective, but the trial is set to continue in order to try and establish conclusive evidence that it can be used to protect whole populations through "herd immunity".

The trial began on 23 March 2015, and so far more than 4,000 close contacts of around 100 Ebola patients have volunteered to be vaccinated. It has been implemented using the same "ring" method that was used to eradicate smallpox. It has been issued to every person who has come into contact with an infected person, thus creating a protective ring around them, which stops the virus spreading further.

Throughout the trial, 50 percent of the rings were vaccinated immediately after the identification of an infected patient and 50 percent of the rings were vaccinated three weeks after the fact, in order that researchers could compare results. In the group that were vaccinated immediately, not a single one went on to develop Ebola. Of those who received the delayed vaccination, only 16 went on to develop Ebola.

With immediate vaccination proven completely effective, randomisation has now ceased. Since 26 July all people who are at risk of contracting Ebola have been vaccinated immediately. Not only could immediate deployment of the vaccine help bring an end to the epidemic, but it will minimise the time needed to gather more conclusive evidence that will eventually be needed to license the product.


Medicins san Frontieres, one of several organisations implementing the trial, is also conducting a parallel by vaccinating all of its frontline workers. "With such high efficacy, all affected countries should immediately start and multiply ring vaccinations to break chains of transmission and vaccinate all frontline workers to protect them," said Bertrand Draguez, MSF's medical director.

In total, nearly 28,000 people have been infected since the outbreak of the West African Ebola epidemic in December 2013. In that time around 11,300 people have died. The outbreak is still ongoing in Guinea, Liberia and Sierra Leone, but the proven efficacy of the VSV-EBOV vaccine now offers hope that the spread of the disease might be halted.

"This is a remarkable result which shows the power of equitable international partnerships and flexibility," said Jeremy Farrar, director of the Wellcome Trust, one of the funders of the trial. "This partnership also shows that such critical work is possible in the midst of a terrible epidemic. It should change how the world responds to such emerging infectious disease threats. We, and all our partners, remain fully committed to giving the world a safe and effective vaccine." "This is Guinea's gift to West Africa and the world," added Sakoba Keita, Guinea's national coordinator for the Ebola response. "The thousands of volunteers from Conakry and other areas of Lower Guinea, but also the many Guinean doctors, data managers and community mobilisers have contributed to finding a line of defence against a terrible disease."