When is an HIV infection prevented and when is it merely delayed?

HN prevention programs are typically evaluated using behavioral outcomes. M athematical models of HIV transmission can be used to translate these behav ioral outcomes into estimates of the number of HIV infections averted. Usua lly intervention effectiveness is evaluated over a brief assessment period and an infection is considered to be prevented if it does nor occur during this period. This approach may overestimate intervention effectiveness if p articipants continue to engage in risk behaviors. Conversely, this strategy underestimates the true impact of interventions by assuming that behaviora l changes persist only until the end of the intervention assessment period. In this article, the authors (a) suggest a simple framework for distinguis hing between HN infections that are truly prevented and those that are mere ly delayed, (b) illustrate how these outcomes can be estimated, (c) discuss strategies for extrapolating intervention effects beyond the assessment pe riod, and (d) highlight the implications of these findings for HIV preventi on decision making.