Opsoclonus-myoclonus-ataxia syndrome (OMAS) is a rare neurological disorder, affecting approximately 0.18 per million individuals annually. It presents with a triad of opsoclonus, myoclonus, and ataxia, often including cognitive dysfunction and behavioral disturbances. Even though OMAS is non-fatal, it frequently follows a chronic-relapsing course, resulting in long-term neuropsychological sequelae in over 50% of patients. Diagnosis is challenging due to variable symptom presentation and the lack of specific diagnostic markers. We report a case of a two-month-old infant who developed OMAS after routine vaccinations, a rare post-vaccination occurrence. Initial treatment with high-dose corticosteroids successfully resolved symptoms, but the patient experienced a relapse during medication tapering. The relapse occurred following another vaccination, suggesting a potential link between the immune response triggered by vaccination and OMAS symptoms. Despite the early relapse, the patient had a favorable recovery, with normal neurodevelopment at 24 months and no further relapses. This case raises awareness of the rare autoimmune post-vaccine reaction as a possible etiology of OMAS, which is infrequently reported in the literature. With this report, we aimed to underscore the importance of early recognition of OMAS, particularly in infants, and highlight the potential for a positive outcome with timely diagnosis and treatment.