Indications for Vaccinations in Preschool Children Subjected to Thymectomy: An Exhaustive Immunological and Clinical Analysis

Neonatal thymectomy during pediatric cardiothoracic surgery causes profound immunological consequences, primarily iatrogenic premature immunosenescence and impaired central tolerance. This review analyzes the mechanisms of thymic deprivation, highlighting the loss of naive T-cells and the compensatory, oligoclonal expansion of memory T-cells. Given the heterogeneity of surgical cohorts, DiGeorge Syndrome (22q11.2DS) serves as a comparative clinical paradigm to establish evidence-based vaccination guidelines. Inactivated vaccines are strongly recommended, although accelerated serological waning demands frequent monitoring and booster doses. Live attenuated vaccines (LAVs), including MMR and Varicella, can be safely administered if strict immunological thresholds (CD4+ ≥400 cells/mmc; CD8+ ≥200 cells/mmc) are surpassed. Conversely, live oral rotavirus and BCG vaccines are strictly contraindicated during severe lymphopenia or in the immediate post-operative window. Crucially, the live-attenuated Yellow Fever vaccine represents an absolute, lifelong contraindication due to the risk of fatal viscerotropic disease. Rigorous flow cytometric and serological pre-vaccination evaluations, alongside permanent clinical documentation of thymic ablation, are essential to ensure safe immunization practices in this vulnerable pediatric cohort.