title: Sexual risk behaviors, circumcision status, and preexisting immunity to adenovirus type 5 among men who have sex with men participating in a randomized HIV-1 vaccine efficacy trial: step study.
abstract: BACKGROUND
  The Step Study found that men who had sex with men (MSM) who received an adenovirus type 5 (Ad5) vector-based vaccine and were uncircumcised or had prior Ad5 immunity, had a higher HIV incidence than MSM who received placebo. We investigated whether differences in HIV exposure, measured by reported sexual risk behaviors, may explain the increased risk.
  
  
  METHODS
  Among 1764 MSM in the trial, 726 were uncircumcised, 994 had prior Ad5 immunity, and 563 were both uncircumcised and had prior Ad5 immunity. Analyses compared sexual risk behaviors and perceived treatment assignment among vaccine and placebo recipients, determined risk factors for HIV acquisition, and examined the role of insertive anal intercourse in HIV risk among uncircumcised men.
  
  
  RESULTS
  Few sexual risk behaviors were significantly higher in vaccine versus placebo recipients at baseline or during follow-up. Among uncircumcised men, vaccine recipients at baseline were more likely to report unprotected insertive anal intercourse with HIV-negative partners (24.9% vs. 18.1%; P = 0.03). Among uncircumcised men who had prior Ad5 immunity, vaccine recipients were more likely to report unprotected insertive anal intercourse with partners of unknown HIV status (46.0% vs. 37.8%; P = 0.05). Vaccine recipients remained at higher risk of HIV infection compared with placebo recipients (hazard ratio = 2.8; 95% confidence interval, 1.2-6.8) controlling for potential confounders.
  
  
  CONCLUSIONS
  These analyses do not support a behavioral explanation for the increased HIV infection rates observed among uncircumcised men in the Step Study. Identifying biologic mechanisms to explain the increased risk is a priority .
authors.affiliation: Laboratory of Infectious Disease Prevention, New York Blood Center, 310 East 67th Street, New York, NY 10065, USA. bkoblin@nybloodcenter.org
authors.forename: Beryl A
authors.initials: BA
authors.lastname: Koblin
authors.forename: Kenneth H
authors.initials: KH
authors.lastname: Mayer
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Noonan
authors.forename: Ching-Yun
authors.initials: CY
authors.lastname: Wang
authors.forename: Michael
authors.initials: M
authors.lastname: Marmor
authors.forename: Jorge
authors.initials: J
authors.lastname: Sanchez
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Brown
authors.forename: Michael N
authors.initials: MN
authors.lastname: Robertson
authors.forename: Susan P
authors.initials: SP
authors.lastname: Buchbinder
mesh_terms: D016915:AIDS Vaccines / Q000276:immunology*; D000260:Adenoviruses, Human / Q000276:immunology*; D000293:Adolescent; D000328:Adult; D002944:Circumcision, Male / Q000706:statistics & numerical data*; D004311:Double-Blind Method; D015658:HIV Infections / Q000453:epidemiology* / Q000517:prevention & control; D015497:HIV-1 / Q000276:immunology*; D018451:Homosexuality, Male; D006801:Humans; D008297:Male; D008875:Middle Aged; D010919:Placebos / Q000008:administration & dosage; D012309:Risk-Taking; D016896:Treatment Outcome; D055815:Young Adult
chemical_list: D016915:AIDS Vaccines; D010919:Placebos