Incidence of Early Revaccination After Pediatric Allogeneic Hematopoietic Stem Cell Transplant

ABSTRACT

Background: Infections are a common cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation (HSCT). Prolonged immune recovery post-HSCT increases the risk of infection and raises concern for poor response to vaccinations. Reimmunization is recommended for all pediatric HSCT patients by transplant and infectious disease organizations1,2, and individual institutions often develop revaccination guidelines. Objective: At Vanderbilt Children's Hospital (VCH), the clinical practice guideline (CPG) instituted in June 2015 recommends early initiation (6 months) of reimmunization in immunologically appropriate patients, starting with Haemophilus influenzae type B (Hib) and pneumococcal conjugate (PCV13) vaccinations. Therefore, we examined the feasibility of early vaccination for allogeneic HSCT patients and determined the causes of delayed or lack of vaccination. Methods:A retrospective chart review of the electronic medical record was conducted under an IRB-approved protocol. Data was gathered and entered in a REDCap database, including dates of vaccination, immune reconstitution studies (IgG concentration, T/B cell subsets) and clinical outcomes [e.g., intravenous immunoglobulin (IVIg) administration, graft versus host disease (GvHD), relapse] through 6-month (+/- 30 days) post-HSCT. Early revaccination was defined as Hib and PCV13 administration within 210 days post-HSCT. Patients not meeting this definition were further examined for factors that led to delay or lack of vaccinations. Patients were included if they were alive without underlying disease progression or graft failure 6-months post-HSCT. Results: Between June 15, 2015 and June 30, 2021, 66 patients met inclusion criteria. Early revaccination occurred in 21/66 patients (32%). Of the 45/66 (68%) that did not receive 6-month vaccinations, the most common reason was concern for impaired immune reconsti- tution (n = 33/45, 73%). Indicators of poor immune recovery included recent IVIg administration (n = 15), ongoing immunosuppression (n = 24), and poor B cell recovery (n = 4);many patients had multiple indications. Other reasons for delay included patient or parent refusal (n = 4), prioritization of COVID vaccinations (n = 3), scheduling conflicts (n = 4), and other (n = 1). Conclusions: Early vaccination occurred in 32% of patients. At 6 months post-HSCT, 50% of patients had poor immune reconstitution resulting in appropriate vaccination delays. However, scheduling conflicts and vaccine hesitancy despite eligibility were small but significant contributors, accounting for 17% of delays. This is a small, single center study but highlights significant challenges with delivery of best practice guidelines. Future directions could include engagement with other institutions regarding best practices to address vaccine hesitancy and to further explore if early revaccination reduces risk of infectious complications post-HSCT.