 This is a randomized, observer-blind, placebo-controlled, parallel-group, multicenter, Phase 2 study evaluating the safety, tolerability and immunogenicity of 3 heterologous prime-boost regimens using Ad26.ZEBOV as prime and MVA-BN-Filo as boost vaccination, administered at 28-, 56- and 84-day Group 1, 2 and 3 as above intervals, in healthy adults and elderly participants. A 28- and 56-day Groups 1 and 2, as above schedule will be evaluated in HIV-infected participants and in healthy children in 2 age strata. The study consists of a screening phase of up to 8 weeks, a vaccination phase in which participants will be vaccinated at baseline Day 1 followed by a boost vaccination on Day 29, 57 or 85, a post-vaccination phase and long-term follow-up phase until Day 365. Participants in Cohort 1 substudy Group 1 and 2 who received Ad26.ZEBOV and MVA-BN-Filo at selected sites will receive Ad26.ZEBOV as third vaccination and who received placebo will receive placebo as third vaccination at least 1 year post prime vaccination. All participants within a cohort will be followed in a blinded manner by the site until the last subject in that cohort has completed the study. This study will be conducted in Africa and the enrollment will take place sequentially in three cohorts: the first cohort will consist of healthy participants 18 - 70 years; the second cohort 2a will include HIV-infected participants 18 to 50 years and healthy children 12 to 17 years cohort 2b; the third cohort will include children aged 4 to 11 years inclusive will be enrolled. Within each cohort, participants will be randomized in a 5:1 ratio to receive active vaccine versus placebo. Safety evaluations will include assessments of adverse events, an electrocardiogram ECG for adult participants at screening, physical examination, vital signs blood pressure, pulseheart rate, body temperature, clinical laboratory and pregnancy testing. An independent data monitoring committee IDMC will be established to monitor data on a regular basis to ensure the continuing safety of the participants enrolled in the study. 