Vaccination Recommendations and Clinical Characteristics of Children after Allogeneic Hematopoietic Stem Cell Transplantation

To investigate the clinical characteristics, the risk factors related to antibody-negative conversion, and the effectiveness and safety of revaccination in children who underwent allogeneic hematopoietic stem cell transplantation (Allo-HSCT). The clinical characteristics of 516 children after Allo-HSCT who were eligible for revaccination in the Vaccination Evaluation Clinic of Shanghai Children's Medical Center from March 2017 to March 2023 were analyzed. Of the 516 patients enrolled, 464 (89.9%) had started revaccination, with a median time of 2.1 (IQR, 1.8-2.6) years after transplantation and 1.1 (IQR, 0.7-1.5) years after cessation of immunosuppressive therapy. There were 418 cases of hepatitis B surface antibody (HBsAb) seropositive before transplantation, and 339 cases (81.1%) became negative at the time of evaluation after transplantation. The visit time for children with persistently HBsAb seropositive was 1.9 (IQR, 1.3-2.3) years after transplantation, which was shorter than the time for children with HBsAb seronegative (2.2 [IQR, 1.9-2.8] years, P<0.001). HBsAb negative conversion was related to the HBsAb titers pre-transplantation, with a lower proportion of high titers in the negative conversion group (4.7% vs. 17.7%, P<0.001). Both univariate and multivariate analyses suggested that HBsAb seroconversion was statistically related to uncompleted three doses of the hepatitis B vaccine before transplantation, low pre-transplantation antibody titers, and ≥2 years after transplantation. Among 40 patients with HBsAb seronegative who received hepatitis B vaccination, 39 (97.5%) had HBsAb titers converted to seropositive. The immune response rates of measles, mumps, and rubella (MMR) were 96.6% (28/29), 69.0% (20/29,) and 88.5% (23/26), respectively. There were no serious adverse side effects after revaccination.After Allo-HSCT, standard evaluation procedures for revaccination are highly recommended. The immune response rates after hepatitis B and MMR revaccination were highly recommended. No severe adverse side effects were observed.