Extended Follow-Up Confirms Early Vaccine- Enhanced Risk of HIV
MAJOR ARTICLE Extended Follow-up Confirms Early Vaccine- Enhanced Risk of HIV Acquisition and Demonstrates Waning Effect Over Time Among Participants in a Randomized Trial of Recombinant Adenovirus HIV Vaccine (Step Study) Ann Duerr,1 Yunda Huang,1 Susan Buchbinder,2 Robert W. Coombs,3 Jorge Sanchez,4 Carlos del Rio,5 Martin Casapia,6 Steven Santiago,7 Peter Gilbert,1 Lawrence Corey,1 Michael N. Robertson,8 and for the Step/HVTN 504 Study Team 1Fred Hutchinson Cancer Research Center, University of Washington, Seattle, 2San Francisco Department of Public Health, California, 3Departments of Laboratory Medicine & Medicine, University of Washington, Seattle; 4Asociacion Civil Impacta Salud y Educacion, Lima, Peru; 5Department of Medicine, Emory University School of Medicine and Emory Center for AIDS Research, Atlanta, Georgia; 6Asociacion Civil Selva Amazonica, Iquitos, Peru; 7Care Resource, Miami, Florida, and 8Merck Research Laboratories, West Point, Pennsylvania Background. The Step Study tested whether an adenovirus serotype 5 (Ad5)–vectored human immunodefi- ciency virus (HIV) vaccine could prevent HIV acquisition and/or reduce viral load set-point after infection. At the first interim analysis, nonefficacy criteria were met. Vaccinations were halted; participants were unblinded. In post hoc analyses, more HIV infections occurred in vaccinees vs placebo recipients in men who had Ad5- neutralizing antibodies and/or were uncircumcised. Follow-up was extended to assess relative risk of HIV acquisi- tion in vaccinees vs placebo recipients over time. Methods. We used Cox proportional hazard models for analyses of vaccine effect on HIV acquisition and vaccine effect modifiers, and nonparametric and semiparametric methods for analysis of constancy of relative risk over time.
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