Introduction: In recent years, influenza has become a major problem threatening the health and economy of people worldwide, making vaccination promotion an important issue. Message format has played an important role in promoting vaccination willingness. While prior studies have explored the effectiveness, extensively exploring conditions for applicability and moderating factors based on external aspects, they have given limited attention to the audience's internal state during message processing. Ego depletion, a common internal state, is known to influence message processing and communication effectiveness.


Purpose: The present study aimed to investigate the interaction between ego-depletion and message format in vaccination willingness, as well as its underlying mechanisms. In addition, natural time as a proxy for ego-depletion seeks to enhance the external validity.


Method: Two web-based experiments using 2 (ego-depletion: high vs. low) × 2 (message format: narrative vs. non-narrative) factorial designs were conducted (N=473), which manipulated ego depletion through both a lab-based Stroop task and a natural time-of-day proxy.


Results: Study 1 experimentally manipulated ego depletion level (high vs. low). Results showed that under high depletion, the narrative message significantly enhanced vaccination willingness compared to the non-narrative messages, whereas this advantage was absent under low depletion. Study 2 examined ego depletion in a naturalistic setting. Results showed that in the evening (when depletion is typically higher), the narrative message significantly enhanced vaccination willingness compared to the non-narrative messages, whereas this advantage was absent in the evening (when depletion is typically higher). Message processing fluency mediated interaction effect: the mediating role of fluency was significant under high ego depletion but not under low ego depletion.


Conclusions: This research demonstrates the role of dynamic cognitive states in narrative and non-narrative persuasion. Furthermore, it offers a practical strategy for message timing, suggesting that narrative messages may be prioritized for communication in the evening.