Background and Objectives: Even something distinctly personal, as an attitude towards vaccination, is actually a social phenomenon that can be influenced by what others do or say. Rich history of persuasion research shows that different types of messages can influence attitude change in diverse directions. The aim of this study was to evaluate the effects of message features on attitudes towards COVID-19 vaccine and vaccination. Methods: Experimental study was conducted in two phases. In the first phase the preexisting attitudes towards COVID-19 vaccination were assessed. In the second phase respondents were randomly assigned to four message interventions, developed combining two prototypical pro-vaccination decision narratives (determined vs. hesitant) with two communication sources (physician vs. lay peer). After the message exposure, participants were asked to fill in the questionnaire regarding attitudes towards COVID-19 vaccination again. Total of 172 adults aged 18 and above from Western Balkans, both vaccinated and unvaccinated, participated in the study. Wilcoxon signed-rank test was applied. Results: The message condition where the lay peer is expressing hesitant decision narrative elicited change in attitudes towards the COVID-19 vaccine safety in both the unvaccinated (p<0.05) and the vaccinated (p<0.05) producing positive change among the former and negative in the latter. Additionally, in the vaccinated the same message condition yielded a significant positive change in perception of the danger of disease (p<0.05) and social responsibility (p<0.05). After the message intervention they perceived danger of COVID-19 as higher and reported greater sense of social responsibility. Conclusions: The same message features elicited different directions of attitude change, depending on vaccination status. In the unvaccinated the exposure to the message enhanced the adoption of message-consistent vaccination attitudes, while in the vaccinated it triggered general sense of vulnerability, characteristic for their pre-vaccination emotional state.