Recombinant 9-valent Human Papillomavirus vaccine (Shanghai Bovax Biotechnology)

After briefly suspending the 2-valent human papillomavirus (HPV) vaccine in 2013, Japan's Ministry of Health, Labour, and Welfare (MHLW) reinstated the recommendation that people receive the newly approved and updated 9-valent HPV vaccine in 2022. We investigated the influence of anticipated regret (AR) and spontaneous thought on individuals' willingness to receive the HPV vaccine, as the 2013 controversy over the HPV vaccine's side effects could lead to public distrust, impeding vaccination coverage despite government-funded initiatives. Using a Japanese-speaking online panel, we conducted a randomized controlled study based on a 3 (Intervention 1, questionnaire for AR: AR for inaction [ARI] vs. AR for action [ARA] vs. without AR) × 2 (Intervention 2, spontaneous thought: task with spontaneous thought vs. distraction) factorial design. Those assigned to the ARI scenario in Intervention 1 were given messages highlighting AR for HPV infection if they did not receive the vaccine, whereas those assigned to the ARA scenario were given messages emphasizing AR for the vaccine's side effects if they were vaccinated; participants assigned to the without AR group were given messages being not emphasizing any AR. In Intervention 2, participants assigned to the spontaneous thought group had 3 min to write freely their opinions about the HPV vaccine. In contrast, those assigned to the distraction group were asked to think about the HPV vaccine. After Intervention 2, we assessed the effects using several questionnaires. Among the 2140 participants, those in the ARI and those in the spontaneous thought groups expressed that female children would be highly willing to get vaccinated. However, no significant main effect of spontaneous thought on male children's willingness to get vaccinated was found; participants in the ARI and spontaneous thought conditions expressed the highest degree of willingness. In summary, spontaneous thought can mitigate the negative impacts of AR in a purely experiential setting.