Safety and Immunogenicity Study of GSK Biologicals' Investigational Recombinant Chimpanzee Adenovirus Type 3-vectored Ebola Zaire Vaccine (GSK3390107A) in Adults in Africa

The purpose of this study is to assess the safety and immunogenicity of the investigational ChAd3-EBO-Z vaccine administered to approximately 3 000 adults in Africa as a single IM dose Considering the risk of exposure to Ebola and the potential (based on animal data) for the investigational ChAd3-EBO-Z vaccine to afford at least partial protection, all subjects in the study will receive the investigational ChAd3-EBO-Z vaccine. The subjects in the Group EBO-Z will receive the vaccine at Day 0 of the study, whereas the subjects in the Group Placebo/ EBO-Z will receive a placebo at Day 0 (as a control) and will receive the investigational ChAd3-EBO-Z vaccine at Month 6, provided that no safety concerns are raised. In addition, vaccinating all subjects in the study with the investigational ChAd3 EBO Z vaccine will allow an increase of the safety database of the investigational vaccine. In case the geographic range of Ebola virus Zaire (EBOV) transmission expands to encompass any of the regions where this trial is conducted, earlier administration of the investigational ChAd3-EBO-Z vaccine to the subjects in the Group Placebo/ EBO-Z will be considered in that region.