Safety and immunogenicity of rVSVΔG-ZEBOV-GP Ebola vaccine in adults and children in Lambaréné, Gabon: A phase I randomised trial

Abstract

Background: The rVSVΔG-ZEBOV-GP vaccine prevented Ebola virus disease when used at 2 × 107 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 × 103, 3 × 104, 3 × 105, 3 × 106, or 2 × 107 PFU in 115 adults and a dose of 2 × 107 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 × 104, 3 × 105, 3 × 106, or 2 × 107 PFU had a ≥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 ≥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 ≥3 × 105 PFU. Adults with antibodies before vaccination had higher GMTs throughout. Neutralising antibodies were detected in more than 50% of participants at doses ≥3 × 105 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 × 107 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.

Fig 1. Participant flow diagram.

Randomisation and flow of participants over a period of 6 months for adults (cohorts 1 to 5), adolescents (cohort 6; 13–17 years), and children (cohort 7; 6–12 years). Similar dose groups are matched with shading (light grey, 3 × 10⁶ PFU; dark grey, 2 × 10⁷ PFU). GP, glycoprotein; ELISA, enzyme-linked immunosorbent assay; PFU, plaque-forming units; rVSV, recombinant vesicular stomatitis virus.

Fig 2. Viral load in saliva for children and adolescents.

rVSVΔG-ZEBOV-GP (rVSV) RNA copy numbers in saliva presented as log10 rVSV RNA copies/ml from day 2 and 7 (d2 and d7) post-injection in adolescents and children vaccinated with 2 × 10⁷ PFU. The broken line denotes the limit of quantitation, and the dotted line denotes the limit of detection. About 67% (12/18) and 30% (6/20) adolescents and children, respectively, had samples above the limit of quantification at day 7. *P < 0.05; **P < 0.01.PFU, plaque-forming units.

Fig 3. Glycoprotein antibody distribution by age group: Comparison of distribution of ZEBOV-GP IgG antibodies (AEU/ml) measured by USAMRIID ZEBOV-GP ELISA for dose 2 × 10⁷ PFU administered to children, adolescents, and adults from day 0, 28, 56, 84, and 180.

Data were not available for children and adolescents at D84. P < 0.05 indicates a statistical difference in ZEBOV-GP IgG between children, adolescents, and adults. AEU, arbitrary enzyme-linked immunosorbent assay units; ELISA, enzyme-linked immunosorbent assay; GP, glycoprotein; PFU, plaque-forming units; USAMRIID, US Army Medical Research Institute of Infectious Diseases; ZEBOV, Zaire Ebola virus.

Fig 4. Antibody responses to whole-virion ELISA (AEU/ml) by age group: Comparison of geometric mean concentration of IgG antibodies for children, adolescents, and adults vaccinated with the 2 × 10⁷ PFU dose at day 0, 28, and 56.

P < 0.05 indicates a statistical difference in antibody concentrations between age groups at the measured time points. AEU, arbitrary enzyme-linked immunosorbent assay units; ELISA, enzyme-linked immunosorbent assay; PFU, plaque-forming units; ZEBOV, Zaire Ebola virus.