Willingness to participate in HIV vaccine trials among a sample of men who have sex with men, with and without a history of commercial sex, Rio de Janeiro, Brazil.

The study objective was to assess willingness of men who have sex with men (MSM) enrolled in a vaccine preparedness study ('Projeto Rio') to participate in phase III anti-HIV/AIDS vaccine trials. Overall, 57% of Projeto Rio participants stated they would participate in a putative vaccine trial. MSM who reported commercial sex work were significantly (p < 0.05) more likely to engage in risky behaviours than others. In bivariate analysis, commercial sex workers (CSWs) were significantly (p < 0.05) more likely than non-commercial sex workers (NCSWs) to be willing to participate in vaccine trials (62.6% versus 51.4%). Among those willing, CSWs reported significantly more often (p < 0.05) (50.5%) than NCSWs (38.0%) that they would enroll to protect themselves from HIV. In multivariate analyses, variables associated with willingness to participate (WTP) were lower educational level, positive serology for syphilis, and 'engagement, under the influence of alcohol, in risky sexual practices that would normally be avoided', but not commercial sex work. The potential enrollment in vaccine trials of MSM CWSs, as well as participants of low socio-economic status and high risk, seems thus to be possible.