From educational seminars to interpersonal diffusion: knowledge fidelity in word-of-mouth transmission of HPV vaccine information in Japan—a real-world implementation study

Abstract Background In vaccine-hesitant environments, evidence-based health information often spreads through interpersonal word-of-mouth communication within community networks. However, little empirical evidence exists regarding whether health knowledge remains accurate as it is transmitted across individuals. HPV vaccine hesitancy has persisted in Japan despite accumulating scientific evidence supporting vaccine safety and effectiveness. Conventional public health communication strategies have had limited impact in restoring public confidence. Implementation science emphasizes the importance of understanding how evidence-based interventions and information spread within real-world social contexts. Diffusion of innovations theory suggests that health information may spread through interpersonal communication within social networks, progressing from innovators to early adopters and subsequently to wider community members. However, empirical evidence regarding whether knowledge transmitted through interpersonal communication is preserved during the diffusion process remains limited. Methods This community-based observational pre–post study evaluated cervical cancer prevention seminars conducted by trained public health nurses in multiple regions of Japan between July 2023 and November 2024. Seminar participants (second learners) completed questionnaires assessing HPV vaccine–related knowledge immediately before and after the seminars. Participants were encouraged to share the information with family members or friends through interpersonal word-of-mouth communication, supported by a printed handout summarizing key messages. Individuals who subsequently received this information were defined as third learners and completed the same questionnaire online. Knowledge responses were categorized as correct, incorrect, or “do not know.” Knowledge fidelity was defined as the extent to which knowledge gained by second learners after the seminar was preserved when transmitted to third learners. Item response theory was used to estimate latent knowledge scores, and knowledge fidelity indices were calculated to quantify the proportion of knowledge gain retained during diffusion. Results A total of 299 second learners completed the pre-seminar questionnaire, 187 completed the post-seminar questionnaire, and 42 third learners completed the post-transmission survey. Correct response rates increased across all six knowledge items among second learners following the seminars. When information was transmitted to third learners through word-of-mouth communication, correct knowledge levels remained higher than baseline levels observed before the seminars. The estimated knowledge fidelity index indicated that approximately 45% of seminar-related knowledge gain was retained during interpersonal transmission, demonstrating that a substantial proportion of evidence-based information was preserved during community diffusion. Regional analysis revealed variation in knowledge fidelity across communities, suggesting that contextual factors may influence how accurately information is preserved during diffusion. Conclusions Structured word-of-mouth communication within community networks can facilitate the transmission and partial retention of HPV vaccine knowledge beyond initial educational seminars. These findings suggest that interpersonal communication within trusted community networks may serve as a real-world implementation pathway for disseminating evidence-based health information in vaccine-hesitant contexts.