<p>As marketing is increasingly expanding from the commercial domain to governance strategy, public health branding and promotional communication for the COVID-19 vaccine were essential for national authorities trying to transfer the WHO communication strategy and vaccine policies to their domestic contexts while maintaining public trust. The aim of this study is to explore the role of (de)legitimation in the COVID-19 vaccine communication (#ROVaccinare/ ROVaccination) policy transfer and branding conducted by the Romanian government on Facebook. Adopting a top-down and bottom-up approach to the sensemaking process of the message strategy promotion, we employed a mixed-methods approach and drew on categorizations of message tailoring related to health communication and operationalizations of discursive (de)legitimation. The main findings showed a preference for rationalization legitimation through the usage of fact-based posts and a clear integration of authorization and narrativization into the message strategy promotion of the ROVaccination page. But despite the prevalence of fact-based posts, legitimation through personal and medical stories were positive predicators of engagement unlike legitimation through facts. The bottom-up approach revealed polarized attitudes towards healthcare professionals as sources of the campaign, the Romanian medical system and towards past and present vaccination. The dominance of polarization in online users’ comments emphasizes their role of agents of conversion contesting either the message sources employed in the campaign or other commenters as personal authorities.</p>