This interventional study targets female students in junior middle school. It goal is to evaluate the effectiveness of a vaccine chatbot on HPV vaccine awareness and vaccination. The main questions it aims to answer are:

1. How will the novel digital tool, a vaccine chatbot, impact eligible parents' awareness and knowledge of HPV vaccines, their willingness to vaccinate their daughters, and vaccination status of female students.
2. How is the vaccine chatbots accepted by all stakeholders, and what are the facilitators of and barriers to implementing vaccine chatbot promotion campaign.

The intervention group will go through the intervention measure while the control group will not:

1. The intervention group will be invited to use the HPV vaccine chatbot online through WeChat , the mostly widely used social media platform in mainland China, or any web browsers. They can ask any questions related to the HPV vaccine and get validated answers from the chatbot immediately. The intervention lasts two weeks, with invitations sent every four days to reinforce the intervention.
2. The control group will not use the chatbot during the intervention duration.

Researchers will compare participants' HPV vaccine awareness, and vaccination intention and status after intervention between intervention group and control group to evaluate if the vaccine chatbot improves HPV vaccine awareness and vaccination.

This is a cluster randomized trial consisted of 2 arms to evaluate the effectiveness of a vaccine chatbot on parents' HPV vaccine awareness, knowledge, and vaccination intention and status regarding their daughters in junior middle school.

The sample size was calculated based on the primary outcome, which is the HPV vaccination rate among middle school girls, and the main analysis method, which involves comparing differences in rates or means before and after the intervention. According to a literature review, the current HPV vaccination rate among female students is around 5%. The investigators assumed that the vaccination rate could increase to between 10% and 12% following the intervention. The minimum sample size was calculated to be between 369 and 648 participants in each group, with a significance level (α) of 0.05, a test power (1-β) of 0.8, and a cluster design effect (D) of 1.5.

Multi-stage sampling will be employed. Firstly, three representative cities will be selected to represent the megacity, general urban city, and rural counties in China, respectively. Then, within each city, three or four middle schools will be selected based on economic development, school size, geographical location. Next, around six classes will be randomly selected for each of the three grades in each middle school. For all the female students who have not be vaccinated against HPV in selected classes, one of their parents will be included in the study. A total of around 162 classes are expected to be included, with around 54 classes in each city.

Stratified cluster randomized grouping will be employed. All classes will be grouped into intervention group or control group by class at a 1:1 ratio, stratified by city, school, and grades, resulting with around 81 classes into the intervention group and 81 in control group. Approximately 600 parents (300 in intervention group; 300 in control group) are expected to participate in the study in each city, with a total sample size of 1,800 parents, meeting the sample size requirement.

Baseline survey will be conducted before the intervention. Then, the intervention group will be invited to use the HPV vaccine chatbot online through WeChat or any web browsers, where they can ask any questions related to the HPV vaccine and get validated answers from the chatbot immediately. The intervention lasts two weeks, with invitations sent every four days to reinforce the intervention. The control group will not use the chatbot during the intervention duration. After 2 weeks, follow-up survey will then be conducted. HPV vaccination status of female students will be collected after 4 months.

The Generalized Estimating Equations (GEE) and mixed-effects analysis methods were employed to control for the effects of covariates and evaluate the intervention effect of the chatbot.

Besides impact evaluation, this study will also conduct an implementation science study, using the RE-AIM (Reach, Effectiveness, Adoption, Implementation, and Maintenance) framework to comprehensively assess the cost-effectiveness, applicability, and scalability of the HPV vaccine chatbot intervention in real-world. Both quantitative and qualitative methods will be used to evaluate its implementation across the above-mentioned five dimensions: reach, effectiveness, adoption, implementation, and maintenance.

Inclusion Criteria:

• Parents of female students in middle school;
• The students not vaccinated or appointed for HPV vaccination and without contraindications to HPV vaccines;
• Without mental disorders or visual/reading impairments, and able to cooperate with and undergo the intervention activities;
• Obtained informed consent and willing to participate in the study.

Exclusion Criteria:

• Students vaccinated or appointed for HPV vaccination or with any contraindication to HPV vaccines;
• With mental disorders or visual/reading impairments, and unable to cooperate with and undergo the intervention activities;
• Unwilling to participate.

Individual participant data that underlie the results reported in the article, after de-identification (text, tables, figures, and appendices), will be shared upon reasonable requests. A written data-sharing request for meta-analysis should be submitted by email with a methodologically sound proposal. Proposals should be directed to zyhou@fudan.edu.cn; to gain access, data requestors will need to sign a data access agreement.

Beginning 12 months and ending 36 months following article publication

Researchers who provide a methodologically sound proposal for meta-analysis. Proposals should be directed to zyhou@fudan.edu.cn; to gain access, data requestors will need to sign a data access agreement.