At the 3rd International HIV Treatment as Prevention Workshop in Vancouver, Canada, in April 2013 I was asked to put forward the case that “Pre-Exposure Prophylaxis (PreP) is not an essential component of Treatment as Prevention (TasP)”. So my job was to convince the public that while PreP may be a useful, and even an important, addition to TasP it is by no means an essential component of TasP. Here I reproduce my argument and invite readers of the SACEMA Quarterly to express their own views on this important issue.
The 6th IAS conference was held from 17-20 July 2011 in Rome. Although the conference is on HIV pathogenesis, treatment & prevention, the main focus this year was on the role of treatment in prevention. This prevention strategy can take different forms. First, by the immediate initiation of antiretroviral therapy (ART) after an HIV positive diagnosis, with a view to reducing a patient’s viral load and hence infectiousness. A second option is the use of a microbicide containing an antiretroviral, to reduce the probability of HIV negative people becoming infected. Finally, treatment as prevention can take the form of pre-exposure prophylaxis (PrEP) whereby antiretrovirals are used by individuals at high risk of exposure to HIV infection. The interim results of the FEM-PrEP trial showed that Truvada does not have a protective effect in women. But at the IAS conference the results of two new studies (the Partners PrEP trial and the TDF2 trial) on the use of oral PrEP in heterosexual people were extensively discussed. For these trials it was estimated that PrEP reduced the risk of transmission by between 62 and 78%.
The focus of this paper is to evaluate PrEP alongside ART and condom-use interventions in South Africa, informed by national HIV and demographical surveys. The age-structured model we developed pays close attention to the distribution of relative infection risks between age categories. It includes dynamical effects usually not explicitly modelled, such as age-dependent condom use and partner choice. Despite some the limitations of the model, the model offers a relatively simple approach to studying the impact of PrEP in the context of national and generalized HIV epidemics. The inclusion of an age variable offers a direct way of studying age-structured prioritising strategies.