A silver lining of the horrific Ebola outbreak that struck West Africa in 2014–15 was that it offered scientists a rare opportunity to field test candidate drugs and vaccines that might be used in future outbreaks. The New York Times now reports that a paper just published by The Lancet confirms that one vaccine, produced by Merck and tested in Guinea, offers excellent and fast protection against the deadly virus. (The study team, led by researchers at the World Health Organization [WHO], had published similar results in August 2015 based on a smaller data set.) Because Ebola cases were already becoming rarer when the study started in April 2015, the scientists used a highly unusual "ring vaccination" design, in which people around a new case were offered the vaccine, either immediately or 3 weeks later. The vaccine has yet to be approved by regulatory authorities, but funding from GAVI, the Vaccine Alliance has allowed Merck to produce a stash of 300,000 doses for emergency use should the virus resurface. One drawback: It was designed specifically for the strain that hit West Africa and has not been tested against other Ebola strains.