Immunity Gaps and Delayed Vaccination Assessment in Children After Hematopoietic Stem Cell Transplantation: A Single-Center Real-World Assessment

Objectives: Hematopoietic stem cell transplantation (HSCT) is curative for many children with high-risk hematologic diseases but can lead to loss of vaccine-acquired immunity, leaving survivors highly susceptible to vaccine-preventable diseases (VPDs). Although systematic revaccination is recommended internationally, real-world evidence from China is scarce. This study described post-HSCT antibody levels, vaccination practices, and parental attitudes and identified factors affecting timely vaccination assessment. Methods: This single-center real-world study included 211 pediatric HSCT survivors attending a dedicated post-transplant vaccination clinic (June 2022–December 2024). Antibody titers against six VPDs were measured at the first visit, before revaccination. Clinical data were extracted from medical records; parental questionnaires captured vaccination status, adverse events, and willingness. Chi-square tests and logistic regression identified factors associated with hepatitis B surface antibody (HBsAb) positivity. Results: HBsAb positivity was 30.54% (62/203), and other antibody positivity ranged from 12.5% to 43.3%. Immunosuppressant exposure > 2 years was independently associated with lower HBsAb positivity (OR = 0.457, 95% CI: 0.244–0.859, p = 0.015). The median interval from HSCT to first assessment was 34 months (IQR: 29–43). Among 161 vaccinated children, adverse reactions were limited to transient fever in 5 (3.1%). Parental willingness was high (94.9%, 188/198), yet 18.7% remained unvaccinated; the leading barrier was unmet clinical criteria (51.4%), followed by community health center refusal (29.7%) and parental safety concerns (18.9%). Conclusions: Substantial immunity gaps and delayed vaccination assessment persist despite high parental willingness, with clinical ineligibility the primary barrier. These findings support closer monitoring of immunosuppressive therapy and immune recovery, alongside coordinated specialist–community pathways, to improve vaccination coverage and timeliness in HSCT survivors.