Why do people take part in vaccine trials? A mixed methods narrative synthesis.

Objectives: To understand why individuals do or do not take part in vaccine trials, exploring the motivators and barriers to identify effective strategies to optimise recruitment in vaccine research.

Methods: Qualitative studies and quantitative surveys capturing data on reasons for trial participation/decline were included. Six databases were searched from 1996 to October 2021. Two reviewers independently screened and assessed risk of bias. Results were reported narratively and analysed using thematic analysis.

Results: We included 32 studies (17 qualitative; 12 quantitative; 3 mixed-methods) that covered a wide range of populations, geographical areas and disease types. Eight themes were identified 1) altruism; 2) potential for personal benefit; 3) perceived risks; 4) trust or distrust; 5) social networks; 6) stigma; 7) practical implications; 8) research vanguard.

Conclusion: Our findings provide a detailed description of how potential participants weigh up their decisions to participate in vaccine trials, which could inform the planning and implementation of studies to enhance recruitment.

Practice Implications: Clinical trial researchers should consider a patient-centered approach to recruitment, tailoring promoting material and attempt to understand fears, stigma and perceived risks. In addition, recognising the importance of trust and the key role friends, communities, family, and those in supervisory positions play in decisions.