The vaccine is meant to protect uninfected people from Ebola, and, if effective, would be tested next in populations in high-risk areas such as west Africa, where the outbreak is ongoing, to immunize them against the virus. It does not contain live Ebola virus, but does contain snippets of its protein coat, just enough to alert the immune system to produce antibodies and immune cells that can recognize and destroy any live viruses that people might eventually encounter. The pieces of Ebola protein are introduced to the body via another virus, one related to the common cold that infects chimps.

The shot was tested in two doses among 10 people each; it triggered antibodies and immune cells that in primate studies were enough to protect them against a challenge of Ebola up to 10 months later. Whether that’s also the case among people won’t be known until the vaccine is tested among thousands more in west Africa, including health care workers and family members of ill patients, who are most vulnerable to getting exposed to the virus.

Only two people reported brief fevers after getting vaccinated.