Impact of DTaP-IPV and DTaP Vaccination Among Adult Allogeneic Hematopoietic Stem Cell Transplant Recipients: A Prospective Observational Study

<b>Background/Objectives</b>: Hematopoietic stem cell transplantation (HSCT) can potentially cure hematological malignancies; however, post-transplant patients have a high risk of infection owing to their immunocompromised status. Vaccination against pathogens, such as diphtheria, tetanus, pertussis, and polio, is essential post-transplantation, but neither the long-term efficacy of vaccines nor the optimal vaccination schedule has been fully established. <b>Methods</b>: In this prospective observational study, we assessed the short- and long-term immunogenicity of three doses of the diphtheria, tetanus, acellular pertussis, and inactivated poliovirus (DTaP-IPV) vaccines or DTaP vaccines in 29 adult allogeneic HSCT (allo-HSCT) recipients, with antibody levels measured at baseline, 1-3 months post-vaccination, and 1-year after vaccine completion. <b>Results</b>: At baseline, a substantial proportion of patients lacked protective antibody levels for the targeted pathogens. However, within 1-3 months post-vaccination, seropositivity rates significantly increased, reaching 78-100% for diphtheria, tetanus, pertussis, and poliovirus. Despite this, antibody levels significantly declined 1-year post-vaccination, especially for pertussis, with only 58-65% of patients maintaining protective levels. In contrast, 85-96% of patients retained protective levels for diphtheria, tetanus, and poliovirus, although antibody values also decreased. Compared to human leukocyte antigen (HLA)-mismatched cases, HLA-matched cases showed significantly higher antibody levels for diphtheria, pertussis, and poliovirus types 1 and 3. <b>Conclusions</b>: This study demonstrates the short-term effectiveness of DTaP-IPV and DTaP vaccines in adult allo-HSCT patients but emphasizes the challenge of maintaining long-term immunity. Given the difficulties in sustaining long-term vaccine efficacy in allo-HSCT recipients, particularly in HLA-mismatched cases, re-evaluating the current vaccination schedule may be necessary to maintain protection.