OBJECTIVES : This study aims to compare the estimates made in the ex-ante and ex-post Budget Impact Analysis (BIA) for incorporation of palivizumab into the Brazilian Public Health System - SUS, identifying the parameters that may result in discrepancies between the analysis.

METHODS : For the external validation of the ex-ante BIA, informations were collected from the national databases to identify and characterize the population eligible for prophylaxis and the costs related to the technology (purchase price for palivizumab, total cost of hospitalization by respiratory syncytial virus (RSV) infection) as well as research in the literature to determine the market share, since such information was not available. Four scenarios were developed. The scenario 1 being elaborated with the data available in the national databases, taking into account the national protocol for the use of palivizumab. The other three scenarios were developed by calibrating the eligible population, excluding the children who were born in 2011 and 2012 and were eligible to the prophylaxis with palivizumab in 2013 of the first year after the incorporation of palivizumab, adjusting the percentage of the eligible population with Congenital Heart Disease (CHD) according to expert opinion, adjustment of the eligible population with Bronchopulmonary Dysplasia (BPD) using values founded in the literature. This last scenario is the sensitivity analysis.

RESULTS : An expense higher than that estimated in the ex-ante BIA was observed, ranging from $ 19 million to $ 183 million over the four year horizon (2013 to 2016) depending on the scenario involved in the validation.

CONCLUSIONS : This study shows that it is necessary to monitor new technologies after its incorporation, validating the financial impact projections made prior to incorporation. Discussion about this theme is important to define the best methodology and what differences between the results of ex-ante and ex-post BIA would be acceptable.