In the trial, experts used a “ring vaccination” strategy—the same strategy used to help eradicate smallpox—which involved inoculating clusters of adults who had come into contact with Ebola patients, and contacts around those contacts, such as neighbors, classmates, or extended family. Some of the clusters inoculated were whole villages, some were sections of towns or cities. In each experimental cluster, some people were vaccinated immediately, while others were vaccinated after 21 days, the maximum incubation period for the Ebola virus.
Researchers found that, in those inoculated immediately (4,123 people), there were no new cases of Ebola at least 10 days afterwards. Among those inoculated after 21 days (3,528 people), there were 16 cases of Ebola. Including all the adults in the study, researchers estimated that the vaccine was more than 75% effective.
The clinical trial in Guinea “has been more successful than we almost could have hoped for,” said one of the study’s senior authors, John-Arne Rottingen, adjunct professor of global health and population at Harvard T. H. Chan School of Public Health and head of infectious disease control at the Norwegian Institute of Public Health, in a July 31, 2015 New York Times article.