Abstract: According to studies on the impact of comments on the false consensus effect, exposure to other people’s reactions can elicit misperceptions, in turn influencing message acceptance. We investigated whether comment valence dominance and comment order were related to false consensus in the context of the flu vaccine controversy. Results from an experimental study suggest that the false consensus effect mediated the relationship between comment valence dominance and attitude toward the flu vaccine. Moreover, comment valence dominance strengthened the false consensus effect in participants with a pre-existing negative attitude toward the flu vaccination. Findings have theoretical and practical implications for social perception bias and health communication.