Randomized controlled trial was conducted in post-splenectomy patients aged >12 years. Subjects are randomly assigned to two groups (zinc and placebo). 1.5 mg/kg/day (max 50 mg/day) of Zinc is administered. Anamnesis, physical examination, and laboratory results such as peripheral blood, ferritin, transferrin saturation, serum zinc, immunologic markers for cellular immunity (lymphocyte count, CD4+ and CD8+ T lymphocyte count and functions) are evaluated at the start and end of the 12-week study.