Potential Epidemiological Impact of Pre-Exposure Prophylaxis
Potential Epidemiological Impact of Pre-Exposure Prophylaxis
The standard PrEP intervention based on an annual budget of $20 million (at scale after 5 years) produces an impact of 24 603 (~11%) infections averted (2015–2025). The estimated number of infections averted increases gradually during the first 5 years of scale-up, with approximately 3400 new infections averted annually thereafter (Fig. 2a). However, assuming that aspects of a PrEP programme are dynamic, the total impact could be as large as 49 450 or a low as 3750 infections averted. This translates to a cost per infection averted between $2060 and $36 360, respectively (Fig. 2b) – a 17-fold difference.
(Enlarge Image)
Figure 2.
Interactions between key parameters could enhance or erode the impact and cost per infection averted for a given preexposure prophylaxis intervention. (a) Blue scenarios allow 'positive' relationships between these parameters as indicated in the legend; red scenarios allow 'negative' relationships between these parameters as indicated in the legend. The impact projections accumulate the additional assumptions so that, for example, the outermost projections show the combined effects of all the relationships. (b) Corresponding estimates of cost per infection averted (from a PrEP programme perspective) for each scenario. Both cost and impact are discounted at an annual rate of 3%. PrEP, pre-exposure prophylaxis.
The strongest determinant of this variation is the ability to prioritize PrEP to those at highest risk of acquisition, due to a large differential in incidence between highest-risk individuals and the wider population. Adherence has a similarly strong influence as adherence determines the level of protection received from PrEP. The relationship between cost and programme size also has considerable effect, as the cost of PrEP directly controls the level of coverage reached, due to the fixed-budget assumption. Improved residual protection has a relatively small effect, as residual protection only applies to missed doses.
Results
The standard PrEP intervention based on an annual budget of $20 million (at scale after 5 years) produces an impact of 24 603 (~11%) infections averted (2015–2025). The estimated number of infections averted increases gradually during the first 5 years of scale-up, with approximately 3400 new infections averted annually thereafter (Fig. 2a). However, assuming that aspects of a PrEP programme are dynamic, the total impact could be as large as 49 450 or a low as 3750 infections averted. This translates to a cost per infection averted between $2060 and $36 360, respectively (Fig. 2b) – a 17-fold difference.
(Enlarge Image)
Figure 2.
Interactions between key parameters could enhance or erode the impact and cost per infection averted for a given preexposure prophylaxis intervention. (a) Blue scenarios allow 'positive' relationships between these parameters as indicated in the legend; red scenarios allow 'negative' relationships between these parameters as indicated in the legend. The impact projections accumulate the additional assumptions so that, for example, the outermost projections show the combined effects of all the relationships. (b) Corresponding estimates of cost per infection averted (from a PrEP programme perspective) for each scenario. Both cost and impact are discounted at an annual rate of 3%. PrEP, pre-exposure prophylaxis.
The strongest determinant of this variation is the ability to prioritize PrEP to those at highest risk of acquisition, due to a large differential in incidence between highest-risk individuals and the wider population. Adherence has a similarly strong influence as adherence determines the level of protection received from PrEP. The relationship between cost and programme size also has considerable effect, as the cost of PrEP directly controls the level of coverage reached, due to the fixed-budget assumption. Improved residual protection has a relatively small effect, as residual protection only applies to missed doses.