Impact of digital communication message on HPV vaccine decision-making among Japanese mothers: A randomized controlled trial

Background: In Japan, human papillomavirus (HPV) vaccine uptake has been hindered by public distrust and misinformation. Understanding which message components can effectively influence mothers' vaccine decision-making is critical for restoring confidence and improving coverage. Objective: To assess the impact of different message components on mothers' willingness to vaccinate their daughters against HPV. Methods: This study employed an online 2 × 2 × 2 × 2 between-person factorial randomized controlled trial with a nationally representative sample of 1439 Japanese mothers of daughters aged 11–18. Participants were randomly assigned to view one of 16 digital text-based messages varying by four components: messenger (individual or organization), content (effectiveness or safety), style (storytelling or scientific data), and misinformation (misinformation or factual information). Outcomes were willingness to vaccinate, confidence in vaccine safety and effectiveness, message trust, and concern about HPV-related diseases. Logistic regression and model fit statistics were used to assess the impact of components. Results: Among 1324 mothers analyzed, messages with factual information significantly increased willingness to vaccinate daughters compared to misinformation (25.9 % vs. 11.3 %; OR = 2.75; 95 % CI = 2.02–3.74), while trust was higher for organizational messages (91.6 %; OR = 1.58; 95 % CI = 1.10–2.27). Storytelling messages increased concerns about HPV-related diseases more than scientific data (40.4 % vs. 31.9 %, OR = 1.45; 95 % CI = 1.15–1.82). Although factual information and trusted sources positively influenced attitudes, a single digital message was insufficient to significantly increase vaccination uptake. Furthermore, misinformation reduced confidence in vaccine safety and effectiveness. Conclusions: Digital messages containing factual information and delivered by organizations positively influence mothers' intentions to vaccinate their daughters against HPV in Japan. These findings support strategies that emphasize trusted sources and factual content while countering misinformation to improve vaccine confidence and uptake. The study was registered at Clinicaltrials.gov (NCT06347627).