SUMMARY: This study aimed to determine the proportion of varicella non-immune pediatric healthcare workers (HCWs) of the Pediatrics Department of King Chulalongkorn Memorial Hospital and to determine cost-effective strategies for identifying non-immune personnel. A cross-sectional study using a self-administered questionnaire to determine HCWs' histories of chickenpox or 2-dose varicella vaccination was conducted. From a total of 699 HCWs, 653 HCWs (93z), including 145 physicians (22z), 297 nurses (46z), and 211 administrative staff (32z), responded to questionnaires. There were 475 HCWs (73z) who had a history of chickenpox, 58 (9z) who had completed the 2-dose varicella vaccine schedule, and 120 (18z) whose varicella-zoster virus (VZV) immunity status was uncertain. In total, 107 HCWs (89z) were tested for VZV IgG, 90 of whom had immunity, and 17 were determined to be non-immune. After combining history and VZV IgG test results, the prevalence of non-immune HCWs was 2.6z (95zCI 1.4-3.8), with those 40 years of age at higher risk of nonimmunity. Implementing a strategy that involves testing of only those with an unknown VZV status and vaccination for only those determined to be non-immune costs 1,801 United States dollar (USD), less than the total cost (4,601 USD) for vaccinating all HCWs with uncertain status