Author(s): Robb ML, RerksNgarm S, Nitayaphan S, Pitisuttithum P, Kaewkungwal J, , Robb ML, RerksNgarm S, Nitayaphan S, Pitisuttithum P, Kaewkungwal J,
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Abstract BACKGROUND: The Thai phase 3 HIV vaccine trial RV 144 showed modest efficacy of a vaccine against HIV acquisition. Baseline variables of age, sex, marital status, and risk did not modify vaccine efficacy. We did a post-hoc analysis of the trial's data to investigate behavioural risk and efficacy every 6 months after vaccination. METHODS: RV 144 was a randomised, multicentre, double-blind, placebo-controlled efficacy trial testing the combination of the HIV vaccines ALVAC-HIV (vCP1521) and AIDSVAX B/E to prevent HIV infection or reduce setpoint viral load. Male and female volunteers aged 18-30 years were recruited from the community. In this post-hoc analysis of the modified intention-to-treat population (16,395 participants), HIV risk behaviour was assessed with a self-administered questionnaire at the time of initial vaccination in the trial and every 6 months thereafter for 3 years. We classified participants' behaviour as low, medium, or high risk. Both the acquisition endpoint and the early viral-load endpoint were examined for interactions with risk status over time and temporal effects after vaccination. Multiple proportional hazards regression models with treatment and time-varying risk covariates were analysed. FINDINGS: Risk of acquisition of HIV was low in each risk group, but 9187 (58·2\%) participants reported higher-risk behaviour at least once during the study. Participants classified as high or increasing risk at least once during follow-up were compared with those who maintained low-risk or medium-risk behaviour as a time-varying covariate, and the interaction of risk status and acquisition efficacy was significant (p=0·01), with greater benefit in low-risk individuals. Vaccine efficacy seemed to peak early--cumulative vaccine efficacy was estimated to be 60·5\% (95\% CI 22-80) through the 12 months after initial vaccination--and declined quickly. Vaccination did not seem to affect viral load in either early or late infections. INTERPRETATION: Future HIV vaccine trials should recognise potential interactions between challenge intensity and risk heterogeneity in both population and treatment effects. The regimen tested in the RV 144 phase 3 trial might benefit from extended immunisation schedules. FUNDING: US Army Medical Research and Materiel Command and Division of AIDS, National Institute of Allergy and Infectious Disease, National Institutes of Health. Copyright © 2012 Elsevier Ltd. All rights reserved.
This article was published in Lancet Infect Dis
and referenced in Journal of AIDS & Clinical Research