Immunogenicity of a 5‐dose pneumococcal vaccination schedule following allogeneic hematopoietic stem cell transplantation

The optimal schedule of pneumococcal vaccination after allogeneic hematopoietic stem cell transplantation (allo‐HSCT) remains controversial. The objective of this study was to investigate the immunogenicity of a 5‐dose pneumococcal vaccination schedule in adult allo‐HSCT recipients with and without immunosuppressive therapy. In this prospective cohort study, allo‐HSCT recipients received four doses of the 13‐valent pneumococcal conjugate vaccine (PCV13) and one dose of the 23‐valent pneumococcal polysaccharide vaccine (PPSV23) starting 4–6 months after allo‐HSCT. PCV13 was administered at T0, T1, T2, and T8 (T = months from enrollment) and PPSV23 at T10. Serum was collected at T0, T4, T8, T10, and T12, and IgG levels were measured for all 24 vaccine serotypes by immunoassay. The primary outcome was overall seroprotection at T12 defined as an IgG concentration ≥1.3 μg/ml for 17/24 vaccine serotypes in allo‐HCST recipients with and without immunosuppressive therapy at baseline. Secondary outcomes were serotype‐specific seroprotection and dynamics of IgG levels. We included 89 allo‐HSCT recipients in the final analysis. Overall seroprotection was 47% (15/32) for patients without immunosuppressive therapy at baseline versus 24% (11/46) for patients with immunosuppressive therapy (p = .03). Seroprotection was higher for PCV13 serotypes (78% and 54% respectively; p = .03) and lower for PPSV23‐unique serotypes (28% and 13% respectively; p = .1). IgG concentrations increased significantly over time for all 24 serotypes. Concluding, although immunogenicity of PCV13 serotypes was reasonable, the poor response to PPSV23 serotypes resulted in an insufficient overall response to pneumococcal vaccination for allo‐HSCT recipients. Research into vaccination strategies with higher‐valent T‐cell‐dependent pneumococcal vaccines is needed.