An interventional study of Default-style LLM chatbot and Conversational-style LLM chatbot in HPV Vaccination Intent, sponsored by University of Pennsylvania. Completed at 1 site in United States. Open to participants aged 18 Years and older, including healthy volunteers. Per ClinicalTrials.gov, last updated 2025-08-20.
Sponsored by University of Pennsylvania · Not applicable, Interventional, and Prevention
The goal of this clinical trial is to test whether short conversations with large language model (LLM) chatbots can persuade vaccine-hesitant parents to vaccinate their children against human papillomavirus (HPV). The study compares two chatbot styles to official public health information and to a no-message control. Parents of HPV-eligible children first complete a survey about their attitudes toward the HPV vaccine and their main concerns. They are then randomly assigned to read public health materials, have a three-minute conversation with either a default-style chatbot or a conversational-style chatbot tailored to their concern, or receive no message. The main outcome is change in intent to vaccinate immediately after the intervention, with follow-up surveys at 15 and 45 days.
University of Pennsylvania is the lead sponsor of 1,635 studies on the registry; 239 are open to participants now.
Of its 154 completed or terminated interventional studies of FDA-regulated products, 104 (68%) have results posted.
Counted across the registry records on this site, refreshed daily.
Exclusion Criteria:
A large language model chatbot (GPT-4o) that delivers tailored persuasive messages to parents about HPV vaccination, using the model's default style with longer, structured responses. Participants engage in a three-minute, multi-turn conversation, with responses personalized to their top-rated vaccine concern identified in a pre-intervention survey.
Behavioral: Default-style LLM chatbot
A large language model chatbot (GPT-4o) that delivers tailored persuasive messages to parents about HPV vaccination in a conversational style, with short responses. Participants engage in a three-minute, multi-turn conversation, with responses personalized to their top-rated vaccine concern identified in a pre-intervention survey.
Behavioral: Conversational-style LLM chatbot
Official public health informational materials on HPV vaccination from the Centers for Disease Control and Prevention (U.S.), National Health Service (U.K.), or Public Health Agency of Canada, matched to the participant's country of residence. Materials are 589-680 words in length, cover HPV risks and benefits of vaccination, and are presented for three minutes before participants proceed.
Behavioral: Public health informational materials
No Intervention
A large language model chatbot (GPT-4o) that delivers tailored persuasive messages to parents about HPV vaccination, using the model's default style with longer, structured responses. Participants engage in a three-minute, multi-turn conversation, with responses personalized to their top-rated vaccine concern identified in a pre-intervention survey.
A large language model chatbot (GPT-4o) that delivers tailored persuasive messages to parents about HPV vaccination in a conversational style, with short responses. Participants engage in a three-minute, multi-turn conversation, with responses personalized to their top-rated vaccine concern identified in a pre-intervention survey.
Official public health informational materials on HPV vaccination from the Centers for Disease Control and Prevention (U.S.), National Health Service (U.K.), or Public Health Agency of Canada, matched to the participant's country of residence. Materials are 589-680 words in length, cover HPV risks and benefits of vaccination, and are presented for three minutes before participants proceed.
Change in intent to vaccinate child against HPV within the next 12 months
Self-reported likelihood, on a 0-100 scale, of vaccinating the participant's youngest HPV vaccine-eligible child (identified in pre-survey) within the next 12 months. Measured before and immediately after the intervention to assess short-term changes in vaccination intent.
Time frame: Baseline to immediately post-intervention
Change in intent to vaccinate child against HPV at 15-day follow-up
Self-reported likelihood, on a 0-100 scale, of vaccinating the participant's youngest HPV vaccine-eligible child within the next 12 months. Measured at baseline and 15 days after the intervention to assess durability of effects.
Time frame: Baseline to 15 days post-intervention
Change in intent to vaccinate child against HPV at 45-day follow-up
Self-reported likelihood, on a 0-100 scale, of vaccinating the participant's youngest HPV vaccine-eligible child within the next 12 months. Measured at baseline and 45 days after the intervention to assess durability of effects.
Time frame: Baseline to 45 days post-intervention
Change in general parental vaccine hesitancy (PACV-5)
Change in scores on the 5-item Parent Attitudes about Childhood Vaccines (PACV-5) scale. Measured at baseline and immediately after the intervention.
Time frame: Baseline to immediately post-intervention
Change in intent to vaccinate child for influenza and COVID-19
Self-reported likelihood, on a 0-100 scale, of vaccinating the participant's youngest eligible child for influenza or COVID-19 within the next 12 months.
Time frame: Measured at baseline and immediately post-intervention.
Change in importance ratings of HPV vaccine concerns
Change in participant ratings (0-100 scale) of importance for each HPV vaccine concern (list derived from National Immunization Surveys) between baseline and immediately post-intervention.
Time frame: Baseline to immediately post-intervention
Clicks on HPV vaccine appointment scheduling link
Whether participants click a provided link to schedule an HPV vaccine appointment through CVS during the post-intervention survey.
Time frame: Immediately post-intervention
Willingness to donate payment to vaccine education charity
Percentage of survey payment participants choose to donate (0%, 10%, 30%, or 50%) to an immunization-related charity during the post-intervention survey.
Time frame: Immediately post-intervention
Willingness to be recontacted for future research
Participant self-reported willingness (yes/no) to be contacted for future studies
Time frame: Immediately post-intervention
Ratings of empathy, usefulness, and relevance of intervention content
Participant ratings (1-5 scale) of how empathetic, useful, and relevant they found the assigned chatbot conversation or public health reading material.
Time frame: Immediately post-intervention
Plan to share: Yes
This study is completed, as verified in Aug 2025. You cannot join it, but the record below documents what was studied.
Get an email when the registry record changes — status, dates, results — or when someone posts here.
Sign in to followQuestions and observations about this study, from anyone following it. Not medical advice, and not a channel to the study team — their contact details are on the registry record.
Sign in to join the discussion. Reading takes no account; posting does. You choose a display name, and a pseudonym is the default.
Nothing here yet. If you are running this trial, taking part in it, or weighing whether to, this is the place to say so.
University of Pennsylvania