Building Up Facilitators, Breaking Down Barriers: A Scoping Review Mapping Factors that Impact Participation in Vaccine Trials

Background: Vaccine trials are critical for developing and approving vaccines, yet ensuring representative participation remains challenging. The COVID–19 pandemic underscored both the importance of vaccination and the pervasive issue of vaccine hesitancy, a psychological state of indecisiveness when making a vaccine–related decision. This hesitancy extends to vaccine trials, which are essential for generating reliable data on safety, efficacy, and potential side effects. The present scoping review identifies key barriers and facilitators influencing trial participation, focusing on COVID–19 trials for the general population and broader vaccine trials for three underrepresented groups (pregnant women, older adults, and parents). Methods: We conducted systematic PubMed searches (April 1–June 20, 2022) using MeSH terms and keywords to locate relevant biomedical literature on COVID–19 vaccine trial participation. Of 2,924 unique articles, 193 were screened in full, and 56 met inclusion criteria. Results: Safety concerns, mistrust, and lack of information emerged as primary barriers to vaccine trial enrolment. Conversely, altruism, trust in researchers and vaccines, and incentives, especially medical incentives, were identified as facilitators. Understanding these factors is critical for expanding volunteer registries and improving pandemic preparedness. Conclusion: Addressing social, behavioural, and practical determinants of vaccine trial participation can foster greater enrolment and more robust data collection. Insights from this review offer guidance for health authorities aiming to enhance communication strategies and encourage broader participation in vaccine trials, ultimately supporting global efforts to control infectious diseases.