Analytic perspective

Persisting with prevention: The importance of adherence for HIV prevention

Helen A Weiss¹ , Judith N Wasserheit² , Ruanne V Barnabas³ , Richard J Hayes¹ and Laith J Abu-Raddad⁴

¹  Medical Research Council Tropical Epidemiology Group, Department of Epidemiology and Population Health, London School of Hygiene & Tropical Medicine, London, UK

²  University of Washington School of Medicine, Seattle, Washington, USA

³  HIV Vaccine Trials Network, Fred Hutchinson Cancer Research Center, Seattle, Washington, USA

⁴  Program in Biostatistics and Biomathematics, Vaccine and Infectious Disease Institute, Fred Hutchinson Cancer Research Center, Seattle, Washington, USA

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Emerging Themes in Epidemiology 2008, 5:8doi:10.1186/1742-7622-5-8

Published:	11 July 2008

Abstract

Background

Only four out of 31 completed randomized controlled trials (RCTs) of HIV prevention strategies against sexual transmission have shown significant efficacy. Poor adherence may have contributed to the lack of effect in some of these trials. In this paper we explore the impact of various levels of adherence on measured efficacy within an RCT.

Analysis

We used simple quantitative methods to illustrate the impact of various levels of adherence on measured efficacy by assuming a uniform population in terms of sexual behavior and the binomial model for the transmission probability per partnership.

At 100% adherence the measured efficacy within an RCT is a reasonable approximation of the true biological efficacy. However, as adherence levels fall, the efficacy measured within a trial substantially under-estimates the true biological efficacy. For example, at 60% adherence, the measured efficacy can be less than half of the true biological efficacy.

Conclusion

Poor adherence during a trial can substantially reduce the power to detect an effect, and improved methods of achieving and maintaining high adherence within trials are needed. There are currently 12 ongoing HIV prevention trials, all but one of which require ongoing user-adherence. Attention must be given to methods of maximizing adherence when piloting and designing RCTs and HIV prevention programmes.