Changes in willingness to participate in HIV vaccine trials among HIV-negative injection drug users.

Injection drug users (IDUs) represent an important risk group for HIV infection. We assessed correlates of IDUs' willingness to participate (WTP) in HIV vaccine trials, and examined temporal changes in WTP. Participants were enrolled in ALIVE, a prospective study of HIV among IDUs in Baltimore; semi-annual visits include interviews and HIV serology. Questionnaires regarding WTP were administered in 1993-1994 and again in 2001-2002. Logistic regression was conducted to identify correlates of WTP. Wave 1 of the survey included 440 participants; Wave 2 included 582 participants (189 participated in both waves). WTP increased modestly over time (83.4 vs. 86.3%; p = 0.16). Monetary incentives were the strongest predictor of WTP (adjOR = 2.73; 95% CI: 1.72-4.35). High expectations of HIV treatment effectiveness did not predict WTP. In this cohort, WTP remained strong and modestly increased over the study period. These results should be considered in the planning of sampling and retention strategies for future vaccine trials.