Several vaccines against respiratory syncytial virus (RSV) have been commercialized recently. Their immediate immunogenicity in various conditions of immunosuppression, including patients receiving allogeneic hematopoietic stem cell transplantation (HSCT), have been reported in 2025 by different teams, including ours. In immunocompromised patients, the duration of vaccinal humoral protection as well as the relevance of seasonal revaccination is still unknown. By analyzing the kinetics of humoral responses after a single dose of bivalent RSVpreF vaccine over 12 months in 71 HSCT recipients, we show that annual revaccination benefits mostly those primarily vaccinated within the early 18 months after HSCT. We also provide a first evaluation of vaccinal clinical effectiveness in HSCT patients.