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324 HIV Risk Behavior Change in a Phase-III HIV Vaccine Efficacy Trial
B. Bartholow*1, S. Buchbinder2, D. McKirnan3, V. Goli1, C. Celum4, and the VaxGen Study Team5
1CDC, Atlanta, GA, USA; 2San Francisco Dept. of Publ. Hlth., CA, USA; 3Univ. of Illinois, Chicago, USA; 4Univ. of Washington, Seattle, USA; and 5VaxGen, Inc., Brisbane, CA, USA
Background: The potential for increased risk behavior associated with efficacy trial participation has been a prominent concern related to the design, safety, and ethical conduct of trials. This analysis describes HIV risk behavior change and evaluates trial-related factors associated with behavior change over time.
Methods: 5,109 men who have sex with men (MSM) and 309 women at-risk for HIV infection were enrolled into a placebo-controlled efficacy trial of AIDSVAX B/B from 61 sites primarily in North America. HIV risk behavior data were collected at baseline, 6, and 12 months. Participant perceptions of vaccine efficacy and assignment to vaccine or placebo were assessed at baseline and 12 months, respectively. chi2 for trend was used to evaluate HIV risk behavior change over time. GEE was used to model the effects of perceived efficacy and treatment assignment on unprotected anal (UPA) and vaginal (UPV) sex over time.
Results: The proportion of MSM engaging in UPA sex decreased from baseline (58%), to 49% at 6 months, and 50% at 12 months (p = 0.001). Among women, UPV sex decreased from (55%) at baseline to 42% at 6 months, and 39% at 12 months (p = 0.001). For MSM, GEE indicated a reduction in UPA over time (p = 0.001) and an effect of perceived assignment (p = 0.01), after controlling for age (p = 0.001). MSM who perceived receiving vaccine were more likely to engage in UPA sex than men who perceived receiving placebo or were unsure of their assignment (OR = 1.23, 95% CI = 1.09(1.37, p = 0.001). Among women, perceived assignment and vaccine efficacy were not related to UPV sex.
Conclusions: Among MSM and women enrolled in the trial, HIV risk behavior decreased significantly over the first 12 months of study participation. Specific HIV vaccine trial-related risk reduction counseling for MSM perceiving assignment to vaccine may be warranted.
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