Hamadan University of Medical Sciences Journal of Education and Community Health 2820-896X 12 3 2025 09 30 Why Do People Share Vaccine Misinformation on Social Media? A Psychological and Social Analysis 143 150 10.34172/jech.3487 EN Arman Miri https://orcid.org/0000-0002-6710-9639 Akram Karimi-Shahanjarini https://orcid.org/0000-0002-2453-1389 Maryam Afshari https://orcid.org/0000-0001-5967-7575 Leili Tapak https://orcid.org/0000-0002-4378-3143 Saeid Bashirian https://orcid.org/0000-0003-2133-087X Journal Article 10.34172/jech.3487 2025 03 08 2025 08 10 Background: Misinformation sharing on social media is a global concern with varying influencing factors across different societies. Understanding these factors is crucial to designing effective interventions, particularly in non-Western contexts, such as Iran. Methods: This cross-sectional quantitative study used a crowdsourcing survey with chain referral sampling to recruit 600 adult media users in Hamadan, Iran (57.8% women and 42.2% men). A structured questionnaire adapted from validated scales assessed psychological, social, and cognitive factors. Partial least squares structural equation modeling was applied to analyze data with significance set at P<0.05. Results: Key predictors of sharing intention included trust in government (β=0.147, P<0.001), accuracy assessment (β=-0.539, P<0.001), fear of missing out (β=0.110, P=0.003), media dependency (β=0.080, P=0.023), social comparison (β=-0.089, P=0.006), and media fatigue (β=-0.124, P=0.001). Media literacy did not moderate these relationships. Among demographic variables, only education level showed a significant effect (β=-0.12, P<0.01). The results of structural equation modeling indicated good model fit: χ²=112.5, standardized root mean square residual=0.07 (values<0.08 suggest good fit), and normed fit index=0.90 (values>0.90 are acceptable). Conclusion: Our study revealed unique cultural drivers of health misinformation sharing in Iran, highlighting the critical roles of institutional trust and accuracy assessment. The findings emphasize the need for context-specific strategies in developing interventions to combat misinformation.