1. In this mathematical modeling study, pre-exposure prophylaxis (PrEP), when combined with other preventive measures such as annual testing and treatment, could reduce the incidence of HIV infection by around 40% in the years 2014-2020 among the UK men who have sex with men (MSM) population.
2. There was a synergistic effect between testing and treatment where the combined effect was greater than the sum of their respective individual effects.
Evidence Rating Level: 2 (Good)
Study Rundown: In men who have sex with men (MSM) in the United Kingdom, incidence rates of HIV infection have remained relatively stable. The investigators in this study set out to mathematically predict and compare the effectiveness of several existing HIV preventative interventions (and the effect of combining various interventions) for MSM in the UK during 2014-2020. These included traditional prevention techniques such as promoting safe sexual behavior, as well as newer interventions such as pre-exposure prophylaxis (PrEP) implementation.
The study found that the most effective intervention (when the mathematical model was assuming less than or equal to 50% intervention participation) was simply testing for HIV twice per year in the population. When 100% intervention adoption participation was assumed, the model showed that PrEP was the most effective. They also found that the effect of combining annual HIV testing along with test-and-treat (i.e. early provision of ART) programs was greater than simply summing the individual intervention effects. Other intervention combinations did not produce an incidence reduction rates greater than the sum of their individual effects. Of note this is a mathematical modeling study, which limits real-world external validity.
The study was funded by the Health Protection Agency (now Public Health England)
Click to read the study in The Lancet HIV
Relevant Reading: Sexual behavior in Britain: partnerships, practices, and HIV risk behaviours
In-Depth [mathematical model]: This study evaluated the effects of several HIV interventions (both individually and in various combinations) using a mathematical model. The model was developed using the R software package. British MSM aged 15-64 were included in the analysis.
Seven interventions were analyzed, these included: 1) testing for HIV annually, 2) testing for HIV twice per year, 3) test-and-treat program, 4) PrEP, 5) reducing number of repeat sexual partners, 6) reducing number of one-time sexual partners, and 7) reducing amount of unprotected anal intercourse with repeat sexual partners. In addition, seven intervention combinations were tested: 1) annual testing and decreased unprotected anal intercourse, 2) decreased number of repeat sexual partners and decreased unprotected anal intercourse, 3) test-and-treat and annual testing, 4) PreEP and test-and-treat, 5) PrEP and decreased unprotected anal intercourse, 6) PrEP and decreased number of repeat sexual partners, and 7) all interventions combined except annual testing.
The results showed that assuming 100% intervention participation, PrEP was the most effective at reducing HIV incidence. Other highly effective interventions included: 1) decreasing number of repeat sexual partners, 2) decreasing amount of unprotected anal intercourse, 3) twice-yearly testing, 4) test-and-treat programs. When the intervention participation (“coverage”) was altered, certain interventions became less effective. If a reduction of coverage from 100% to 25% was assumed, the intervention to decrease the number of repeat sexual partners was the most negatively effected, with an effect decrease of 75%. Testing twice yearly was the most robust intervention, being least affected by an assumed decrease in coverage. The only combined intervention that demonstrated an incidence reduction greater than the sum of the individual effects was annual testing along with a test-and-treat program.
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