Previous studies indicated that narrative health messages are more effective than non-narrative messages in influencing health outcomes. However, this body of evidence does not account for differences in health domain, and little is known about the effectiveness of this message execution strategy during public health emergencies. In this study, we examined the relative effectiveness of the two formats in influencing knowledge and perceived response efficacy related to prevention of pandemic influenza, and determined whether effects of message format vary across population sub-groups. Data for the study come from an experiment fielded in 2013 that involved a nationally representative sample of 627 American adults. Participants were randomly assigned to view either a narrative (n=322) or a non-narrative (n=305) video clip containing closely matched information about knowledge and preventive actions related to pandemic influenza, and completed pre- and post-viewing questions assessing knowledge and perceived response efficacy related to the prevention of pandemic influenza. Results indicated that participants in the non-narrative condition reported greater knowledge and rated pandemic influenza prevention measures as more effective compared with those in the narrative condition. Message format effects did not vary across population sub-groups; post-viewing scores of knowledge and perceptions related to pandemic influenza were consistently higher in the non-narrative condition compared with the narrative condition across five socio-demographic groups: age, gender, education, race/ethnicity and income. We concluded that didactic, non-narrative messages may be more effective than narrative messages to influence knowledge and perceptions during public health emergencies.