In an incredible new development, an experimental Ebola vaccine provided 100 percent protection from the deadly virus in a recent trial. Researchers say that the vaccine employs a strategy similar to the one used to eradicate smallpox back in the 1970s by using a method called “ring vaccination,” which would vaccinate people who have been in contact with patients, and those who have been in contact with contacts.

Vaccine efficacy was 100 percent, researchers from the World Health Organization reported in the latest issue of the Lancet medical journal. It’s too late to stop the West Africa Ebola epidemic that killed many thousands, but it could save many lives in the future should another Ebola outbreak threaten the world.

The West Africa outbreak actually helped create the vaccine. Scientists have spent years working on an Ebola vaccine, but found it hard to test because the virus only causes occasional, small outbreaks. When the epidemic started in Guinea, Sierra Leone and Liberia, researchers worked in earnest to finally solve the riddle of Ebola.

“The evidence from all 117 clusters showed that no cases of Ebola virus disease occurred 10 days or more after randomisation among all immediately vaccinated contacts and contacts of contacts versus 23 cases (11 clusters affected) among all eligible contacts and contacts of contacts in delayed plus all eligible contacts and contacts of contacts never vaccinated in immediate clusters,” the paper’s abstract states. “The estimated vaccine efficacy here was 100% (95% CI 79·3–100·0, p=0·0033).

“52% of contacts and contacts of contacts assigned to immediate vaccination and in non-randomised clusters received the vaccine immediately; vaccination protected both vaccinated and unvaccinated people in those clusters. 5837 individuals in total received the vaccine (5643 adults and 194 children), and all vaccinees were followed up for 84 days. 3149 (53·9%) of 5837 individuals reported at least one adverse event in the 14 days after vaccination; these were typically mild (87·5% of all 7211 adverse events).”