The postmodern medical paradigm has empowered online users in the (de)legitimating process of health-related topics. By employing a co-occurrence analysis, this study identifies the thematic patterns used by Romanian online users in their multimodal comments to the #storiesfromvaccination Facebook campaign run by the Romanian government. The findings show that the commenters assessed source credibility through two thematic patterns: 'source exemplarity' and 'source distrust'. Health experts were more legitimized than laypersons and role models as sources in the COVID-19 vaccination campaign. Two thematic patterns emerged in the assessment of vaccination, namely: 'immunization - past and present challenges' and 'vaccination supporter versus opponent cleavage'. In the discussion on immunization, a polarization between a nostalgic longing for the past and a present corrupted medical and political system prevailed, whereas the important feature of discursive antagonism could be observed in the latter thematic pattern. The co-occurrences of (de)legitimation strategies are explained with reference to the political and medical context, along with the challenges of social media usage in online vaccination communication campaigns.