The treatment and management of patients with immunosuppression continue to improve, driven by advancements in therapeutic options, including immunosuppressive agents, monoclonal antibodies, and biologics. Chemotherapy advancements, particularly in molecular-targeted therapies and immunotherapy, have broadened the range of hematological disorders treatable without hematopoietic stem cell transplantation (HSCT). Despite these advances, many patients still require HSCT or solid organ transplantation (SOT) and face a heightened risk of infectious diseases due to immunosuppression [[1], [2], [3], [4], [5]]. Managing infectious diseases in immunosuppressed individuals relies on three fundamental strategies: prophylactic administration of antimicrobial agents, preemptive treatment based on early diagnosis, and immunization [6]. Among these, vaccination is the most crucial, alongside antimicrobial prophylaxis and preemptive therapy guided by early diagnosis [7,8].

SOT and HSCT cause immunodeficiency through different mechanisms. Consequently, the recommended vaccines and their respective schedules vary between these patient populations. Most SOT recipients require lifelong immunosuppression, whereas HSCT recipients typically discontinue them after transplantation, eventually leading to immune reconstitution. Therefore, SOT recipients should ideally be vaccinated before transplantation [9]. Notably, a significant portion of prior immunity is lost in HSCT recipients, necessitating comprehensive post-transplant re-vaccination programs [[10], [11], [12]]. The early post-transplantation period after HSCT is marked by increased susceptibility to infection [10,13]. Although most recommended vaccines are consistent across countries, including Japan, certain aspects of the vaccination protocols differ. Despite differences in various immunodeficiency conditions, vaccination strategies are broadly similar. This review article focuses on vaccination strategies for adult SOT and HSCT recipients in Japan and highlights the disparities between Japan and other countries.