In this study we will invite the 56 participants from the Phase 1 study at two time points: 24 - 30 months and 36 - 42 months after receiving the primary vaccination. Following consenting and enrolment into the study, the participants will undergo a blood test. We will assess the humoral immunity by estimating the level of binding antibody to the Ebola virus envelope glycoprotein. Cellular immunity will be assessed by estimating the functional CD4+ and the CD8+ T cells secreting the pro-inflammatory cytokines. We will undertake this assessment by intracellular staining of the peripheral blood mononuclear cells (PBMC) and using flowcytometry technique to identify the positively stained cells. A second assessment of the cellular immunity will be carried out by an in-house ELISpot technique subject to availability of additional funding.