Developing an interactive, personalized patient decision aid for COVID-19 vaccination in Canada: Insights from a human-centered design and development study

Background: The COVID-19 pandemic highlighted the need for practical digital health tools to support informed decision-making amidst rapidly evolving evidence and widespread misinformation. Objective: We iteratively developed and refined VaxDA-C19, a bilingual (English and French) web-based patient decision aid designed to support informed decision-making in Canada about COVID-19 vaccination. VaxDA-C19 integrates interactive and personalized features aimed to enhance vaccine confidence, reduce cognitive overload, and respond to diverse informational needs. Methods: We developed VaxDA-C19 using an iterative, user-centered design approach. Throughout the development process, we involved a citizen panel, healthcare professionals, user experience designers, and scientific experts to guide refinements. We also conducted usability testing sessions with adults in Canada, using semi-structured interviews, comparative testing, and think-aloud protocols with thematic analysis. We ultimately conducted four design cycles in total: three with adults in Canada (cycle 1: n=9 users; cycle 2: n=22 users; cycle 3: n=3 users), one overlapping and one additional cycle with expert reviewers (cycle 3: n=5; cycle 4: n=9). Results: In Cycle 1, user feedback guided design decisions about how to present quantitative information and technical vaccine descriptions more simply. In Cycle 2, while most users (82%) favored in-depth explanations of vaccine development, a few raised concerns about content that could be perceived as politically charged. Cycle 3 identified usability improvements, including more explicit navigation controls, simplified medical terminology, and optimized interactive components (avatars, sliders). Expert reviews in Cycle 4 refined linguistic consistency, mobile responsiveness, content transparency, and scientific accuracy, emphasizing explicit instructional guidance and bilingual accessibility. Conclusions: Our iterative process produced a personalized, bilingual digital decision aid to support evidence-informed, values-congruent decisions about COVID-19 vaccination. A randomized controlled trial will further evaluate VaxDA-C19's impact on vaccination intentions, knowledge retention, emotional responses, decisional conflict, and decisional regret. If it proves effective, the patient decision aid may also be used as a platform to support other vaccine decisions, namely, influenza, measles, shingles, pertussis, and potentially other emerging infectious diseases.