Seguridad e Inmunogenicidad de la Vacuna Bivalente de Subunidad RSVpreF en Niños de 2 a 18 Años con Seropositividad

Background/Objectives: We aimed to determine safe and immunogenic RSVpreF vaccine dose levels for further clinical development in 2-<18 year olds. Methods: The phase 1, age-descending, open-label Picasso trial evaluated different RSVpreF dose levels in respiratory syncytial virus (RSV)-seropositive 2-<5 year olds and 5-<18 year olds who were either healthy or had chronic medical conditions with increased RSV illness risk. Participants received a single dose of RSVpreF (60 µg or 120 µg dose level). The primary objective was to describe safety and tolerability at each dose level and age group, including frequencies of reactogenicity and adverse events (AEs). The secondary objective was to describe RSV neutralizing antibody responses at each dose level and age group 1 month after vaccination. Results: Overall, 127 participants received RSVpreF 60 µg (2-<5 year olds, n = 20; 5-<18 year olds, n = 35) or 120 µg (n = 24 and n = 48, respectively); 54% were male and 69% were White. Local reactions and systemic events were reported in 17-20% and 33-45% of 2-<5 year olds, respectively, and 49-56% and 52-60% of 5-<18 year olds; most were mild or moderate in severity. AEs were reported in 13-15% of 2-<5 year olds and 8-14% of 5-<18 year olds. No AEs leading to withdrawal or vaccine-related serious AEs were reported. RSV-A and RSV-B neutralizing titer geometric mean fold rises from before to 1 month after vaccination with RSVpreF 60 and 120 µg, which were 17.7-20.6 and 42.8-39.8, respectively, in 2-<5 year olds, and 19.0-23.5 and 20.3-20.3, respectively, in 5-<18 year olds. Conclusions: RSVpreF was safe, well tolerated, and elicited immune responses in RSV-seropositive 2-<18-year-old participants, supporting further clinical development in this pediatric population, including those with chronic conditions.