Immunological responses to tetanus, diphtheria, pertussis (Tdap) vaccine in Brazilian hematopoietic stem cell transplant recipients

INTRODUCTION: Among hematopoietic stem cell transplant (HSCT) recipients, morbidity and mortality are largely related to infectious diseases, many of which are vaccine-preventable. The present study aimed to assess the immune response of HSCT patients to the tetanus, diphtheria, and acellular pertussis inactivated vaccine (Tdap). PATIENTS AND METHODS: This quasi-experimental study, with individually matched data collection in HSCT patients from January 2018 to December 2020, evaluated sixteen patients for their immune response to each of the Tdap components. The immunization schedule included three doses of Tdap, with a minimum interval of 30 days between each dose, starting at 6 months post-transplantation. Immune competence was measured before vaccination by quantifying CD4+, CD8+, and CD19+ frequencies, as well as serum immunoglobulin levels. RESULTS: After the complete immunization schedule, for diphtheria, we observed a Geometric Mean Concentration (GMC) rise from 0.2509 IU/mL at baseline to 0.7544 IU/mL post-vaccination, p = 0.001. For tetanus, GMC increased from 0.353 to 1.153 IU/mL, p = 0.001. For pertussis, GMC was 31.9 IU/mL before and 99.3 IU/mL after vaccination. Due to the non-normal distribution of pertussis data and a marginal frequentist result (p = 0.077), we used Bayesian analysis assuming an exponential distribution. This model identified a significant increase in antibody levels, with a posterior mean difference (θ) of 58.55 IU/mL and a 95% Credibility Interval (23.9-109.0) that excluded zero, confirming an adequate vaccine response. For the entire Tdap vaccination period, CD4+ cell frequencies remained low, while CD8+, CD19+, and immunoglobulin titers remained within normal range. Immune responses to each of the Tdap vaccine components were not affected (p > 0.05) by any of the clinical, demographic, or immunological variables assessed. CONCLUSIONS: The overall Tdap vaccine post-transplant response was considered adequate for diphtheria, tetanus, and pertussis. These findings highlight the immune response to Tdap in transplanted patients and may inform future vaccination guidelines.