Experimental Ebola Vaccine Could Grind Virus to a Halt WHO trial saw zero cases among those tested with new vaccine By Newser Editors and Wire Services Posted Jul 31, 2015 9:15 AM CDT 14 comments Comments In this March 7, 2015 file photo, a health worker, right, cleans a man's arm before injecting him with an Ebola vaccine in Conakry, Guinea. (Youssouf Bah) (Newser) – An experimental vaccine tested on thousands in Guinea exposed to Ebola seems to work and might shut down the epidemic in West Africa, according to interim results from a World Health Organization study out today. "If proven effective, this is going to be a game-changer," said WHO director Dr. Margaret Chan. Scientists have struggled for years to develop Ebola vaccines, with many failed attempts, including a recently abandoned drug cocktail tested in West Africa by Tekmira Pharmaceuticals. "This (vaccine) could be the key that we've been missing to end the outbreak," says a virologist who was not part of the study. "I don't see any reason on humanitarian grounds why it should not be used immediately." He said further tests would show if the vaccine might protect pregnant women, children, and adolescents; those are underway. Researchers gave one dose of the new vaccine, developed by the Canadian government, to more than 4,000 people who were contacts of confirmed Ebola cases within 10 days of being identified. In comparison, more than 3,500 contacts of other Ebola cases got the shot after a 10-day delay. In the group that received the vaccine immediately, there were no Ebola cases versus 16 cases among delayed vaccinations. The vaccine, which has been licensed to Merck, uses an Ebola protein to prompt the body's immune system to attack the virus. "It looks to be about as safe as a flu vaccine," says the virologist. Researchers are still assessing possible side effects; the most serious seemed to be fever and the stress experienced by patients who believe such symptoms were due to Ebola.