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An experimental Ebola vaccine has been declared a success by scientists working to stop the spread of the virus in West Africa, and could mark the end of a long and deadly outbreak.

The trial results were published today in the Lancet medical journal. The World Health Organization (WHO) said in a statement today that "the vaccine up to now shows 100 percent efficacy in individuals," but adds that "more conclusive evidence is needed on its capacity to protect populations through what is called 'herd immunity'."

For now, however, the results mark a huge success. The Canadian drug test was, and will continue to be, tested in Guinea, where more than 2,500 people have died of Ebola as of mid-July this year. Overall, more than 11,000 West Africans have died of the disease in this outbreak.

Guinea's national coordinator for the Ebola response said: "This is Guinea’s gift to West Africa and the world." The trial's success is especially impressive because of its speed. According to the Guardian, the team who carried out the trial were able to achieve in one year what usually takes at least 10.

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That speed, plus the circumstances under which the trial was carried out, means it didn't adhere to the standards of a normal trial: No placebos were administered, and there was a relatively small number of participants. This was also the first time a vaccine was tested using the ring approach, which mandates that all those in the immediate contact with the patient be vaccinated as well (this method was instrumental in fighting Smallpox). The vaccine trial will continue in West Africa.

The drug is licensed to Merck, which purchased the rights to the vaccine last year. The New Yorker 's Vauhini Vara wrote at the time that the company will likely keep drug costs low:

I spoke on Monday with Kevin Outterson, a co-director of the health-law program at Boston University, who studies the economic incentives that influence drug development… More likely [than to make a profit], he said, the companies decided to work on the vaccines because Ebola is such a pressing public-health problem, and they are in a position to help—and, of course, to gain some positive publicity while they’re at it.

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If all goes well, the vaccine could mean the end of Ebola crises.

Danielle Wiener-Bronner is a news reporter.