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Background The rVSV[DELTA]G-ZEBOV-GP vaccine prevented Ebola virus disease when used at 2 x 10.sup.7 plaque-forming units (PFU) in a trial in Guinea. This study provides further safety and immunogenicity data. Methods and findings A randomised, open-label phase I trial in Lambaréné, Gabon, studied 5 single intramuscular vaccine doses of 3 x 10.sup.3, 3 x 10.sup.4, 3 x 10.sup.5, 3 x 10.sup.6, or 2 x 10.sup.7 PFU in 115 adults and a dose of 2 x 10.sup.7 PFU in 20 adolescents and 20 children. The primary objective was safety and tolerability 28 days post-injection. Immunogenicity, viraemia, and shedding post-vaccination were evaluated as secondary objectives. In adults, mild-to-moderate adverse events were frequent, but there were no serious or severe adverse events related to vaccination. Before vaccination, Zaire Ebola virus (ZEBOV)-glycoprotein (GP)-specific and ZEBOV antibodies were detected in 11% and 27% of adults, respectively. In adults, 74%-100% of individuals who received a dose 3 x 10.sup.4, 3 x 10.sup.5, 3 x 10.sup.6, or 2 x 10.sup.7 PFU had a [greater than or equal to]4.0-fold increase in geometric mean titres (GMTs) of ZEBOV-GP-specific antibodies at day 28, reaching GMTs of 489 (95% CI: 264-908), 556 (95% CI: 280-1,101), 1,245 (95% CI: 899-1,724), and 1,503 (95% CI: 931-2,426), respectively. Twenty-two percent of adults had a [greater than or equal to]4-fold increase of ZEBOV antibodies, with GMTs at day 28 of 1,015 (647-1,591), 1,887 (1,154-3,085), 1,445 (1,013-2,062), and 3,958 (2,249-6,967) for the same doses, respectively. These antibodies persisted up to day 180 for doses [greater than or equal to]3 x 10.sup.5 PFU. Adults with antibodies before vaccination had higher GMTs throughout. Neutralising antibodies were detected in more than 50% of participants at doses [greater than or equal to]3 x 10.sup.5 PFU. As in adults, no serious or severe adverse events related to vaccine occurred in adolescents or children. At day 2, vaccine RNA titres were higher for adolescents and children than adults. At day 7, 78% of adolescents and 35% of children had recombinant vesicular stomatitis virus RNA detectable in saliva. The vaccine induced high GMTs of ZEBOV-GP-specific antibodies at day 28 in adolescents, 1,428 (95% CI: 1,025-1,989), and children, 1,620 (95% CI: 806-3,259), and in both groups antibody titres increased up to day 180. The absence of a control group, lack of stratification for baseline antibody status, and imbalances in male/female ratio are the main limitations of this study. Conclusions Our data confirm the acceptable safety and immunogenicity profile of the 2 x 10.sup.7 PFU dose in adults and support consideration of lower doses for paediatric populations and those who request boosting. Trial registration Pan African Clinical Trials Registry PACTR201411000919191, Author(s): Selidji T. Agnandji 1,2,3, José F. Fernandes 1,2, Emmanuel B. Bache 1, Régis M. Obiang Mba 1, Jessica S. Brosnahan 1,2,3, Lumeka Kabwende 1, Paul Pitzinger 1,2,4, Pieter Staarink [...]