 The recruitment of volunteers for preventive vaccine trials is a challenge due to vaccine hesitancy, debates on vaccines, and usual difficulties in clinical trial enrollment. A systematic PubMed search was conducted using Prisma guidelines to identify articles or reviews reporting barriers and motivations to participation in private regardless of the targeted disease or population. Improvements in recruitment could be made through better explanations of the prevented disease, expected individual and collective benefit, ethical protective principles, decision aids, and patient and public involvement. Further perspective and interventional studies are needed to analyze if these leads may improve acceptance level in private. This article was authored by MD Tocque, Agagna Brunon, F Luckt, and others.