OBJECTIVES: Public health care system in Paraguay is highly centralized, compared to other Latin American sectors, and more than half of the population relies on it in order to receive formal treatment. The National Immunization Program (EPI) is not an exemption, affecting the way local/departmental resources in immunization are allocated, impacting on the effectiveness of these investments. In addition, differences in population characteristics among departments, in terms of health care behavior, income and education, and the use of formal medicine patterns by original ethnic groups might affect EPIxs effectiveness. The goal of the paper is to identify how supply side characteristics (financial, managerial and immunization strategies) and demand side factors impact on immunization coverage. METHODS: The document proposes a sequential model, where local health authorities intent to fill the gap in immunization financing and managerial needs, based on the resources allocation and coverage strategy defined by the national health ministry, that leads the Paraguayan immunization design. As a result, a logistic model was implemented, where the likelihood of being vaccinated is tested as a dependent variable, where geographical, educational and ethnical barriers are checked. In addition, supply variables related to financing, coverage strategies and communicational efforts are included. The study analyze data from the Integrated National Household Survey (2001), complemented with a series of immunization effectiveness indexes constructed based on management, financing and vaccine provision criterion, distinguishing among financial sustainability, management effectiveness and antigen supply volatility, collected from official sources and interviews with key personnel by region. RESULTS: Health care policy variables were statistically significant, showing the relevance of social communication, measured in terms of physical, monetary and human resources involved. CONCLUSION: The paper shows the importance of socio-economic-cultural barriers on the probability of being immunized, based on health behavior, presence of formal health insurance, and main source of care (hospital, traditional medicine, etc.).