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

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.