Vaccination in pediatric transplantation-General recommendations. A position paper by the European Reference Network TransplantChild.

Infectious diseases remain a leading cause of morbidity and mortality among pediatric transplant recipients, despite significant advances in transplantation management. Vaccination is the most effective strategy to prevent infections; however, its efficacy is hindered in solid organ transplant (SOT) and hematopoietic stem cell transplant (HSCT) recipients, due to altered immune responses. Pediatric SOT candidates often have incomplete vaccination status prior to transplantation and reduced vaccine efficacy post-transplant due to immunosuppressive therapy. They are also at greater risk of vaccine-preventable infections compared to adults, leading to higher rates of hospitalization, graft loss, and death. In HSCT recipients, immune ablation and reconstitution result in the loss of immunologic memory, rendering both pre- and post-transplant vaccine strategies particularly challenging. Factors such as graft-versus-host disease, immunoglobulin therapy, and ongoing immunosuppression further complicate timing and effectiveness of vaccinations. Despite established guidelines emphasizing timely immunization, several studies report low vaccination coverage and inadequate protective immunity in both groups. Barriers include intercurrent illness, variation in national immunization schedules, vaccine hesitancy, and uncertainties regarding optimal vaccination timing. In this position statement, the European Reference Network (ERN) TransplantChild Working Group conducted a comprehensive literature review on the most relevant studies on vaccinations in pediatric transplant candidates and recipients, with the aim of developing evidence-based recommendations tailored to pediatric SOT and HSCT recipients. This position paper outlines current challenges, summarizes existing evidence, and proposes recommendations to improve immunization practices in this high-risk population.