Preparing for future European efficacy trials of interventions to prevent HIV and other sexually transmitted infections: Lessons on willingness to participate and barriers to participation from ten German clinics serving behaviorally vulnerable men who have sex with men.

Future efficacy testing of interventions to prevent HIV or other infections will require engagement of vulnerable populations. We characterized willingness to participate in a future HIV vaccine trial and barriers to participation among men who have sex with men in a 12-month German cohort study. Among 1015 participants at enrollment, 604 (60%) reported willingness, 60 (6%) were unwilling, 351 (35%) were unsure or refused to answer. Among those unwilling, the primary reason was fear of getting HIV. Among those willing, reasons included protection against HIV and furthering scientific knowledge. In a multivariable logistic regression model, higher odds of willingness to participate were seen among participants at the 12-month visit (aOR: 1.09, 95% CI: 1.04-1.15) and with prior knowledge of HIV vaccine research (aOR: 1.14, 95% CI: 1.06-1.23). Educating potential participants about vaccine research may facilitate recruitment and participation in future trials of HIV vaccine candidates and other prevention interventions.