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).

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.

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.

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. Competing Interest Statement The authors have declared no competing interest. Funding Statement This work was supported by the VACCELERATE project, which is funded by the European Commission’s activities for future pandemic preparedness under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 101037867). Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Data Availability All data produced in the present study are available upon reasonable request to the authors