Protective antibodies against diphtheria, tetanus, and pertussis following revaccination in children and young adults having undergone haematopoietic stem cell transplantation

Objective: Haematopoietic stem cell transplantation (HSCT) eliminates pre-existing immunity, necessitating revaccination. This study aimed to assess the prevalence of protective antibody titres against diphtheria, pertussis, and tetanus in pediatric and young adult HSCT recipients at least four years post-revaccination. Results: A cross-sectional study was conducted in 94 post-HSCT patients (aged 5–25 years) who completed a three-dose DTP series at least four years prior. Protective anti-tetanus and anti-diphtheria antibody titres were detected in 93.6% and 81.9% of participants, respectively, at least four years post-revaccination. However, only 9.4% had protective anti-pertussis titres, which remained low within five years of revaccination. Factors associated with protective anti-tetanus included higher absolute lymphocyte counts (ALC) 1-year post-revaccination, while corticosteroid use during revaccination was negatively associated. ALC at the 3rd dose of vaccination was associated with a protective anti-diphtheria titre. A booster dose of Tdap resulted in seroconversion in 80.0% for diphtheria, 47.4% for pertussis, and 100% for tetanus. These findings support an earlier booster dose of DTP vaccination in post-HSCT patients.