Text, human voice, or AI voice?: the effects of modality and delivery voice on the persuasive outcomes of public health messages about COVID-19 vaccination among the unvaccinated

This study examines how message modality (text vs. audio) and delivery voice (human vs. AI) within audio messages influence the effectiveness of COVID-19 vaccination messages. In an online experiment with unvaccinated adults (N = 177), participants were randomly assigned to one of three experimentally manipulated conditions: text, human voice audio, or AI voice audio delivering narrative messages about vaccination. Although no significant difference in perceived message effectiveness (PME) emerged between text and audio messages overall, within the audio conditions, human voice messages elicited higher PME than AI voice messages. Mediation analyses indicated that PME fully mediated the relationship between voice type and vaccination intention, such that human voice indirectly increased intention through higher PME. The effects were further conditioned by prior attitudes, such that the relative advantage of human voice over text in shaping PME, and in turn vaccination intention, emerged primarily among individuals with less favourable attitudes. These findings suggest that the effectiveness of message delivery mode is conditional on audience disposition, with human voice offering a distinct persuasive advantage among those whom health campaigns most urgently need to reach.