Academy of Medical Sciences of I.R. Iran Archives of Iranian Medicine 1029-2977 28 11 2025 11 01 Herpes Zoster in a 9-Month-Old Immunocompetent Infant 657 659 10.34172/aim.35002 EN Muath Alammar https://orcid.org/0000-0001-8743-7253 Journal Article 10.34172/aim.35002 2025 08 23 2025 09 21 Herpes zoster (HZ), caused by varicella-zoster virus (VZV) reactivation, is rare in infants, typically linked to maternal VZV exposure during pregnancy. This case describes HZ presentation in a healthy infant without a clear exposure history. A 9-month-old immunocompetent female presented with a two-day fever and unilateral, dermatomal rash of vesicular lesions along the C5 dermatome. Initial misdiagnoses of insect bites or eczema delayed treatment. Diagnostic tests, including Tzanck smear showing multinucleated giant cells, confirmed HZ, with normal blood counts and negative maternal VZV antibodies, suggesting subclinical primary infection. Oral acyclovir (20 mg/kg/dose, five times daily for seven days) led to full recovery without complications. This case highlights HZ as a rare but important differential diagnosis for unilateral vesicular rashes in infants. It underscores the need for research into VZV reactivation mechanisms in early childhood.