BACKGROUND: The 2014 Zaire Ebola virus disease epidemic accelerated vaccine development for the virus. We aimed to assess the safety, reactogenicity, and immunogenicity of one dose of monovalent, recombinant, chimpanzee adenovirus type 3 vectored Zaire Ebola glycoprotein vaccine ChAd3 EBO Z in adults. ...Our findings provide a strong basis for future development steps, which should concentrate on multivalent approaches including Sudan and Marburg strains . ...