People’s opinion around social and political issues is currently witnessed by messages ordinarily posted on socialmedia. With reference to a specific case study,namely the vaccination topic in Italy, this article discusses a crucial aspect in structuring the data processing pipeline in intelligent systems aimed at monitoring the public opinion through Twitter messages: A plain analysis of tweet contents is not sufficient to grasp the diversity of behavior across users. To get a sharper picture of the public opinion as expressed on socialmedia, user-related information must be incorporated in the analysis. Relying on a dataset of tweets about vaccination and on an established text classification system, we present the results of a stance monitoring campaign with advanced analysis on temporal and spatial scales. The overallmethodological workflow provides a sound solution for public opinion assessment from Twitter data.