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BackgroundRespiratory syncytial virus (RSV) remains a leading cause of pediatric morbidity, with no approved vaccine. We assessed the safety and immunogenicity of the Ad26.RSV.preF vaccine candidate in adults and children.MethodsIn this randomized, double-blind, phase 1/2a, placebo-controlled study, 12 adults (18-50 years) and 36 RSV-seropositive children (12-24 months) were randomized 2:1 to Ad26.RSV.preF (1 × 1011 viral particles [vp] for adults, 5 × 1010 vp for children) or placebo, at day 1 and 29, with 6-month immunogenicity and 1-year safety follow-up. RSV infection was an exploratory outcome in children.ResultsIn adults, solicited adverse events (AEs) were generally mild-moderate, with no serious AEs. In children, no vaccination-related serious AEs were reported; fever was reported in 14 (58.3%) Ad26.RSV.preF recipients. Baseline pediatric geometric mean titers for RSV A2 neutralization increased from 121 (95% confidence interval [CI], 76-191) to 1608 (95% CI, 730-3544) at day 29, and 2235 (95% CI, 1586-3150) at day 57, remaining elevated over 7 months. RSV infection was confirmed in fewer children receiving Ad26.RSV.preF (1, 4.2%) than placebo (5, 41.7%).ConclusionsAd26.RSV.preF demonstrated immunogenicity in healthy adults and toddlers, with no safety concerns raised. Evaluations in RSV-seronegative children are underway.

Original publication




Journal article


The Journal of infectious diseases

Publication Date



Oxford Vaccine Group, Department of Paediatrics, University of Oxford, Oxford, UK.