Willingness of injection drug users to participate in an HIV vaccine efficacy trial in Bangkok, Thailand.

We assessed willingness to participate in an HIV recombinant gp120 bivalent subtypes B/E candidate vaccine efficacy trial among 193 injection drug users (IDUs) attending drug treatment clinics in Bangkok, Thailand. IDUs previously enrolled in a prospective cohort study were invited to group sessions describing a potential trial, then completed questionnaires assessing comprehension and willingness to participate. A week later, they completed a follow-up questionnaire that again assessed comprehension and willingness to participate, as well as barriers to and positive motives for participation, with whom (if anyone) they talked about the information, and whether others thought participation was a good, bad, or neutral idea. At baseline, 51% were definitely willing to participate, and at follow-up 54%; only 3% were not willing to participate at either time. Comprehension was high at baseline and improved at follow-up. Participants who viewed altruism, regular HIV tests, and family support for participation as important were more willing to volunteer. Frequency of incarceration and concerns about the length of the trial, possible vaccine-induced accelerated disease progression, and lack of family support were negatively associated with willingness. Overall, IDUs comprehended the information needed to make a fully informed decision about participating in an rgp120 vaccine efficacy trial and expressed a high level of willingness to participate in such a trial.