An experimental Ebola vaccine initially developed by the Public Health Agency of Canada has proven to be “highly protective” against the deadly virus in a major trial in Guinea, according to results published on December 23 in The Lancet. The vaccine is the first to prevent infection from one of the most lethal known pathogens.

The vaccine was studied in a trial involving 11,841 people in Guinea. Among the 5,837 people who received the vaccine, no Ebola cases were recorded 10 days or more after vaccination. In comparison, there were 23 cases 10 days or more after vaccination among those who did not receive the vaccine.