BackgroundHuman papillomavirus (HPV) vaccine hesitancy is on the rise, and provider communication is a first-line strategy to address parental concerns. The use of the presumptive approach and motivational interviewing by providers may not be enough to influence parental decision-making owing to the providers’ limited time, self-efficacy, and skills to implement these strategies. Interventions to enhance provider communication and build parental HPV vaccine confidence have been undertested. Delivering tailored patient education to parents via mobile phones before they visit the health care provider may address time constraints during clinic visits and positively affect vaccine uptake. ObjectiveThis study aimed to describe the development and evaluate the acceptability of a mobile phone–based, family-focused intervention guided by theory to address concerns of HPV vaccine–hesitant parents before the clinic visit, as well as explore intervention use to facilitate parent-child communication. MethodsThe health belief model and theory of reasoned action guided intervention content development. A multilevel stakeholder engagement process was used to iteratively develop the HPVVaxFacts intervention, including a community advisory board review, a review by an advisory panel comprising HPV vaccine–hesitant parents, a health communications expert review, semistructured qualitative interviews with HPV vaccine–hesitant parents (n=31) and providers (n=15), and a content expert review. Inductive thematic analysis was used to identify themes in the interview data. ResultsThe qualitative interviews yielded 4 themes: overall views toward mobile device use for health information, acceptability of HPVVaxFacts, facilitators of HPVVaxFacts use, and barriers to HPVVaxFacts use. In parent interviews after reviewing HPVVaxFacts prototypes, almost all parents (29/31, 94%) stated they intended to have their child vaccinated. Most of the parents stated that they liked the added adolescents’ corner to engage in optional parent-child communication (ie, choice to share and discuss information with their child; 27/31, 87%) and shared decision-making in some cases (8/31, 26%). After incorporating all input, the final intervention consisted of a 10-item survey to identify the top 3 concerns of parents, followed by tailored education that was mapped to each of the following concerns: evidential messages, images or graphics to enhance comprehension and address low literacy, links to credible websites, a provider video, suggested questions to ask their child’s physician, and an optional adolescents’ corner to educate the patient and support parent-child communication. ConclusionsThe multilevel stakeholder-engaged process used to iteratively develop this novel intervention for HPV vaccine–hesitant families can be used as a model to develop future mobile health interventions. This intervention is currently being pilot-tested in preparation for a randomized controlled trial aiming to increase HPV vaccination among adolescent children of vaccine-hesitant parents in a clinic setting. Future research can adapt HPVVaxFacts for other vaccines and use in other settings (eg, health departments and pharmacies).