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Background: The epidemiological patron of hepatitis A has changed in the last few years and a decrease of the anti-hepatitis A antibodies IgG (Anti-HVA) have been observed at early ages, which will accompany in the future an increase of symptomatic hepatitis. The prevention of hepatitis A requires a strict application of the norms of personal and environmental hygiene and the administration of vaccines or immunoglobulins. In order to determine the convenience of immunization actively or passively with or without the previous detection of Anti-HVA, requires the knowledge of with strategy is more efficient., Methods: An analysis is carried out to determine the threshold of prevalence, where the reason of efficiency is established by comparing the unit cost of immunization either actively or passively of the population, with a cost of immunizing only the negative Anti-HVA by previous screening, with the formula: the unit cost of the active or passive immunization (unit cost of screening + cost of active or passive (in specific immunoglobuline) immunization in the negative Anti-HVA). The results correlate with the prevalence of Anti-HVA in age group founded in sero-epidemiological studies published by Salleras (1992 and Pérez-Trallero (1994)., Results: The threshold of prevalence, the reason of efficiency equals 1, it's situated in 18% and 65% respectively for the active and passive immunization, which corresponds to the age group of 10-19 years and 20-29 years based on sero-epidemiological studies used., Conclusions: With prevalence of Anti-HVA equal to or above 18% of the population the most efficient strategy is to determine the Anti-HVA before the active immunization; This threshold of prevalence move to up to 65% with passive immunization. Beneath these prevalence it's more efficient to immunize actively or passively without prior screening.