Objectives: Abandoning condoms for microbicides is termed ‘condom migration'. This study estimated the reduction in condom use that can be tolerated following the introduction of an HIV- and sexually transmitted disease (STD)-efficacious microbicide without increasing an individual's risk of HIV infection, and explored how microbicide use affects HIV-risk.
Design: Development of a static mathematical model to compare how different combinations of condom and microbicide use affect individual risk of HIV and STD infection at a particular point in time.
Methods: The model is used to identify the ‘break-even point’ at which any increased risk associated with condom migration is counter-balanced by the protection afforded with microbicides. Data from Benin is used as a case-example.
Results: Considering a 50% HIV- and STD-efficacious microbicide, groups that use condoms with 25% consistency or less could cease using condoms without increasing their risk if they use microbicides in 50% or more of sex acts. However, migration may increase risk if the initial condom-consistency is high (> 70%) and microbicide-consistency is low (< 50% of non-condom-protected acts). For the Benin case-example, if condoms are initially used in 70% or less of sex acts, and if consistency of condom use is sustained following microbicide introduction, there will be a 20% or greater reduction in HIV-risk if the microbicide is used in 50% of non-condom-protected sex acts.
Conclusions: There are likely to be many situations in which the benefits of microbicide use outweigh the negative impact of condom migration, and where microbicides could substantially reduce HIV-risk.
From the aHealth Policy Unit, Department of Public Health and Policy, London School of Hygiene & Tropical Medicine, London, UK and bGlobal Campaign for Microbicides, PATH (Program for Appropriate Technology in Health), Washington DC, USA.
Correspondence to Anna Foss, Department of Public Health & Policy, London School of Hygiene & Tropical Medicine, Keppel Street, London, WC1E 7HT, UK. Tel: +44 (0)20 7612 7891; fax: +44 (0)20 7637 5391; e-mail: email@example.com
Received: 30 August 2002; revised: 19 December 2002; accepted: 22 January 2003.