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Biostatistics Advance Access published online on April 14, 2005
Biostatistics, doi:10.1093/biostatistics/kxi014
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© The Author 2005. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oupjournals.org.
Received April 12, 2004
Revised December 14, 2004
Accepted December 15, 2004

Article

Failure time analysis of HIV vaccine effects on viral load and antiretroviral therapy initiation

Peter B. Gilbert 1* and Yanqing Sun 2

1 Department of Biostatistics, University of Washington and Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, Seattle, Washington 98109, USA
2 Department of Mathematics and Statistics, University of North Carolina at Charlotte, 9201 University City Boulevard, Charlotte, North Carolina 28223, USA

* To whom correspondence should be addressed.
Peter B. Gilbert, E-mail: pgilbert{at}scharp.org


  Abstract

The world's first efficacy trial of a preventive HIV vaccine completed in 2003. Study participants who became HIV infected were followed for two years and monitored for HIV viral load and initiation of antiretroviral therapy (ART). In order to determine if vaccination may have altered HIV progression in persons who acquired HIV, a pre-specified objective was to compare the time until a composite endpoint between the vaccine and placebo arms, where the composite endpoint is the first event of ART initiation or viral failure (HIV viral load exceeds a threshold xvl copies/ml). Specifically, with vaccine efficacy, V E({tau}, xvl); defined as one minus the ratio (vaccine/placebo) of the cumulative probability of the composite endpoint (with failure threshold xvl) occurring by {tau} months, the aim was to estimate the four parameters {V E({tau}, xvl) : xvl {1500; 10000; 20000; 55000} copies/ml} with simultaneous 95% confidence bands. A Gaussian multipliers simulation method is devised for constructing confidence bands for V E({tau}, xvl) with xvl spanning multiple discrete values or a continuous range. The new method is evaluated in simulations and is applied to the vaccine trial dataset.

Keywords: Gaussian multipliers technique; HIV vaccine efficacy trial; Kaplan-Meier estimator; Simultaneous confidence bands.
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