Persistence of humoral immunity to tetanus and diphtheria in hematopoietic stem cell transplant recipients after post-transplant immunization.
Persistence of humoral immunity was evaluated in 82 hematopoietic stem cell transplant recipients up to 12.5 years after post-transplant immunization against tetanus and diphtheria. New immunization, initiated at least 12 months after transplantation, consisted of an average three-dose schedule of vaccine administration on day 1, month 3, and month 12. Serological data were collected at pre-transplant, post-transplant, vaccination, and post-vaccination time points. The first vaccination dose elicited a seroprotective response in most recipients, but the complete vaccine series (usually three-dose schedule) reinforced the specific immunity in most vaccinated cases, that is, 100% and 95.8% seroprotection against tetanus and diphtheria, respectively. Geometric mean concentration post-vaccination tetanus and diphtheria antibody levels persisted at 1.9 IU (95% CI: 1.23-2.94 IU/ml) and 0.20 IU (95% CI: 0.11-0.38 IU/ml) for 7 years, respectively. However, diphtheria antibodies were lost not significantly but much faster and more often than tetanus antibodies, though the seroprotection rates against tetanus and diphtheria remained favorable, that is, 100% (95% CI: 85.2-100%) and 87% (95% CI: 59.5-98.3%), respectively. Full post-transplant revaccination resulted in long-term persistence of humoral immunity against tetanus and diphtheria in SCT recipients, for an average of 8.6 and 9.0 years, respectively.