Background Although COVID-19 social marketing vaccination campaigns have been developed and vigorously promoted to encourage citizens to vaccinate against COVID-19, many people have not responded to vaccination campaigns. Very little is known about the extent to which vaccination campaigns are effective at overcoming people’s resistance to getting the vaccine. Focus of the Article Integrating social trust into the elaboration likelihood model, the current study proposes a model to analyse the effectiveness of COVID-19 social marketing vaccination campaigns and to examine the extent to which social trust plays a role in influencing people’s perceptions of the effectiveness of COVID-19 social media vaccination campaigns. Research Hypotheses The study proposes hypotheses regarding the influence of argument quality and source credibility in COVID-19 vaccination campaigns on individuals’ perceptions of campaign usefulness. In addition, it suggests that source credibility and perceived usefulness of these campaigns play a role in shaping individuals’ attitudes toward COVID-19 vaccination. Furthermore, the study posits that both attitude and perceived usefulness contribute to individuals’ intentions to take the COVID-19 vaccine. Lastly, the study hypothesises that perceived social trust moderates the impact of perceived usefulness on vaccination intentions. Importance to the Social Marketing Field The study holds significant importance in the field of social marketing for several reasons. Firstly, it contributes to a deeper understanding of the dynamics influencing individuals’ perceptions, attitudes, and intentions related to COVID-19 vaccination campaigns. Secondly, by examining the impact of argument quality, source credibility, and social trust, the study provides valuable insights into the factors that can enhance or hinder the success of vaccination campaigns. The inclusion of perceived social trust as a moderating factor in the study further enhances its importance in the field of social marketing. Understanding the role of social trust in influencing the relationship between perceived usefulness and vaccination intentions is crucial for designing context-specific strategies that account for the broader societal dynamics. Methods Online survey data were obtained from 413 adult South Africans. The partial least squares structural equation modelling technique was used to examine the model and test the hypotheses. Results The study found that the quality of arguments in vaccination campaigns and the credibility of the message sources affected how people viewed the usefulness of the messages and their overall attitudes. Surprisingly, although attitudes influenced individuals’ intentions to get the COVID-19 vaccine, the perceived usefulness of the campaign had no direct impact on vaccination intentions. Notably, the results revealed that low social trust played a role in making the perceived usefulness of the COVID-19 vaccination campaign message insignificant in predicting vaccination intentions. Recommendations for Research/Practice Social marketers aiming to improve vaccination attitudes and intentions should focus on two key strategies: emphasising the usefulness of vaccination by highlighting its benefits and leveraging credible sources like healthcare professionals and community leaders to enhance message trust. In addition, this study emphasises the crucial role of social trust in shaping individual responses to vaccination campaigns. Building trust in governing institutions, healthcare systems, and science can significantly impact vaccination acceptance and promotion. Limitations The limitations include potential social desirability bias influencing responses, the need for longitudinal data to establish causality, and the possibility of other influential factors beyond the study’s scope, such as culture and health literacy.