Initiation of revaccination per the Advisory Committee on Immunization Practices (ACIP) recommendations appears to be delayed for a significant portion of pediatric patients following allogeneic hematopoietic stem cell transplant (allo-HSCT), according to research presented at the 2022 American Society of Pediatric Hematology/Oncology Conference.

Researchers conducted a retrospective cohort study to determine the effect of transplant-related complications and socioeconomic factors on revaccination schedule adherence among pediatric patients following allo-HSCT at Children’s Healthcare of Atlanta (CHOA), in Atlanta, Georgia, between 2010 and 2020. They also assessed whether early trends in revaccination adherence were altered following the establishment of a post-transplant vaccine clinic in 2019.

The researchers used clinical and socioeconomic that had been submitted to the Center for International Blood and Marrow Transplant Research registry, the CHOA Epic electronic health record, and United States Census data to identify eligible pediatric patients (≤21 years of age). Patients were excluded in cases of death, relapse, graft failure, or relocation outside of Georgia prior to post-transplant day 365.

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A total of 289 patients (56% male and 44% female), with a mean age of 9.1±5.6 years at transplant, were included in the study. The cohort was predominantly White patients (45%) and Black patients (44%), and Hispanic/Latinx ethnicity was reported for 14% of patients. Approximately 60% of patients lived in high-poverty census tracts. Allo-HSCT indications were hematologic malignancy (46%), hemoglobinopathy (26%), immune dysregulation/deficiency (14%) and bone marrow failure (14%).

The researchers found that the median delay beyond the ACIP-recommended revaccination start date (180 days post-transplant) was 212 days (interquartile range [IQR], 197) and that the median revaccination delay from the end of graft vs host disease (GVHD) prophylaxis was 340 days (IQR, 212).

They reported that 50% of patients completed the 3-dose pneumococcal conjugate vaccine (PCV-13) series and 3% completed a primary series of PCV-13, Haemophilus influenzae type B (HiB) vaccine, inactivated polio vaccine (IPV), and diphtheria-tetanus-pertussis (DTaP) vaccine. The team also reported that 16% of patients received at least 1 vaccine at the vaccine clinic after its establishment.

Using a logistic regression analysis, the researchers demonstrated that patients with hemoglobinopathies (odds ratio [OR], 1.27; 95% CI, 1.05-1.53; P =.01) and those who attended the vaccine clinic (OR, 1.25; 95% CI, 1.07-1.46; P =.006) were more likely to complete the PCV-13 series. They also showed that patients with chronic GVHD (OR, 0.88; 95% CI, 0.78-0.99; P =.04) or those who received post-transplant intravenous immune globulin (OR, 0.79; 95% CI, 0.71-0.89; P <.001) were less likely to complete the PCV-13 series.

Factors associated with shorter delays to initiation of revaccination were diagnosis of hemoglobinopathy (OR, 0.82; 95% CI, 0.68-0.99; P =.04), coverage by private insurance (OR, 0.83; 95% CI, 0.69-0.99; P =.04), and post-transplant tacrolimus (OR, 0.75; 95% CI, 0.62-0.89; P =.002).

“Few pediatric post-allogeneic HSCT patients initiated revaccination within 90 days of the ACIP recommendations (180 days post-transplant),” wrote the researchers. “The extent of revaccination delays and incomplete revaccinations documented between 2010-2020 supports the importance of a post-transplant vaccine clinic in directly addressing this gap in care, especially for those with risk factors for incomplete revaccination.”

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Yarnall JN, Yarnall E, Khemani K, Haight A, Goggin KP. Clinical and social factors affecting revaccination adherence for pediatric patients after allogeneic hematopoietic stem cell transplant. Presented at: 2022 American Society of Pediatric Hematology/Oncology (ASPHO) Conference; May 4-7, 2022. Abstract 332.