This paper details the development of a corpus with posts in Brazilian Portuguese published by Brazilian political elites on X (formerly Twitter) regarding COVID-19 vaccines. The corpus consists of 9,045 posts annotated for relevance, stance and sentiment towards COVID-19 vaccines and vaccination during the first three years of the COVID-19 pandemic (2020-2022).Nine annotators, working in three groups, classified relevance, stance, and sentiment in messages posted between 2020 and 2022 by local political elites. The annotators underwent extensive training, and weekly meetings were conducted to ensure intra-group annotation consistency. The analysis revealed fair to moderate inter-annotator agreement (Average Krippendorf’s alpha of 0.94 for relevance, 0,67 for sentiment and 0,70 for stance). This work makes four significant contributions to the literature. First, it addresses the scarcity of corpora in Brazilian Portuguese, particularly on COVID-19 or vaccines in general. Second, it provides a reliable annotation scheme for sentiment and stance classification, distinguishing both tasks, thereby improving classification precision. Third, it offers a corpus annotated with stance and sentiment according to this scheme, demonstrating how these tasks differ and how conflating them may lead to inconsistencies in corpus construction, as a results of confounding these phenomena — a recurring issue in NLP research beyond studies focusing on vaccines. And fourth, this annotated corpus may serve as the gold standard for fine-tuning and evaluating supervised machine learning models for relevance, sentiment and stance analysis of X posts on similar domains.