Boomerang effects in influenza vaccination campaigns can undermine immunization efforts by increasing vaccine refusal. To effectively reduce these counterproductive outcomes, practitioners should not only communicate the risks and benefits of influenza vaccination but also consider whether their communication strategies could inadvertently trigger boomerang effects. Understanding why and how these effects occur is therefore crucial. This study investigates the mechanisms and boundary conditions underlying boomerang effects in influenza vaccine communication. Specifically, we examined psychological reactance as the key mechanism, focusing on immediate threats to freedom induced by persuasive messages and message fatigue resulting from prolonged exposure. Additionally, we explored how normative perceptions act as boundary conditions. An online experiment with U.S. adults (N = 648) analyzed via multigroup structural equation modeling revealed that both perceived threat to freedom and message fatigue were significant antecedents of psychological reactance, which was associated with increased vaccine refusal. Furthermore, perceived descriptive norms amplified these associations, whereas injunctive norms did not moderate them. These findings underscore the practical importance of carefully crafting vaccination messages that minimize perceived threats and avoid overexposure while considering social norms to reduce psychological reactance and enhance vaccination uptake.
Li et al. (2026) studied this question.