Humoral Immunity to Vaccine-Preventable Diseases in Childhood Cancer Survivors: A Single-Center Study

Background: Pediatric cancer treatments significantly impair immune memory. This study aims to evaluate the prevalence of protective vaccine-induced antibodies and characterize immune recovery in children following chemotherapy in Algeria. Methods: A prospective study was conducted on 75 pediatric patients (median age: 6 years) in remission after cancer treatment at Mustapha University Hospital. Humoral immunity was assessed for measles, hepatitis B (HBV), diphtheria and tetanus. Cellular immunity and immunoglobulin levels were analyzed at a median of six months post-treatment. Results: Overall, 94.6% of patients exhibited an absence of protective antibodies against at least one vaccine-preventable disease. Seronegativity rates were highest for measles (76%) and HBV (64%), followed by diphtheria (34%) and tetanus (29%). Patients with Acute Leukemia (AL) showed significantly higher rates of tetanus seronegativity compared to those with non-Hodgkin lymphoma (45.2% vs. 6.7%, p = 0.008). Immunological evaluation revealed profound CD4⁺ T-cell lymphopenia in 45% of cases. Age was significantly associated with serological status (HBV: p = 0.01; diphtheria: p = 0.04). Conclusions: A substantial proportion of pediatric cancer survivors lose humoral immunity, particularly against measles and HBV. These findings highlight a critical window of vulnerability and strongly support the implementation of systematic post-treatment serological screening and tailored revaccination strategies.