Antibody response.

IntroductionNational and international guidelines recommend vaccinating hematopoietic stem cell transplant (HSCT) recipients, although relatively few studies have evaluated immunogenicity in adults. We therefore aimed to assess the immune response in adult allogeneic HSCT recipients vaccinated against tetanus, diphtheria, poliomyelitis, hepatitis B, and H. influenzae b.MethodWe conducted a multicenter prospective study. HSCT recipients were included at least 6 months post-transplantation (maximum: 24 months) if blood CD19 + lymphocytes were ≥0.1 G/L and plasma immunoglobulin ≥ 4g/L, and if no immunosuppressive therapy was applied. They received the hexavalent pediatric combination vaccine for tetanus, diphtheria, poliomyelitis, hepatitis B, and H. influenzae b (and pertussis) at months 0, 1, 2, and 12 (in addition to other recommended vaccines). Plasma antibodies against the five valences were quantified at inclusion and 1 month after the third and fourth doses.ResultsWe included 104 HSCT recipients (median age: 58 years [IQR:48–64]). Study vaccination was initiated a median of 11 months [IQR:9–14] after transplantation. Median [IQR] values for CD19 and plasma gammaglobulin at inclusion were 0.3 [0.2–0.6] G/L and 7.9 [6.4–11.1] g/L, respectively. Seroprotection after three doses and after the M12 booster was achieved for 97.2% and 97.5% of participants for tetanus, 100% and 97.5% for diphtheria, 96.6% and 92.7% for poliomyelitis, 78.3% and 84.1% for hepatitis B, and 94.6% and 95.0% for H. influenzae b. Adverse effects were benign.ConclusionVaccination against these five infections initiated during the first year post-allograft is immunogenic and should be performed in every recipient not undergoing immunosuppressive therapy.Trial registrationClinicalTrials.gov NCT03402776