The anti-HIV drug Truvada has been shown to be very effective at preventing new infections when taken by people at high risk who strictly adhere to the drug therapy regime.
A new study suggests just how cost-effective this intervention – known as pre-exposure prophylaxis, or PrEP – could be in Toronto, and says there may be additional benefits to a PrEP program if it brings high-risk individuals into contact with the health-care system and engages them in care.
Researchers at St Michael’s Hospital developed a mathematical model to evaluate the impact of PrEP on the number of new HIV infections among gay men in Toronto, the number of HIV-related deaths averted and the cost impact on the health-care system.
Previous studies have found that a daily dose of Truvada, a Health-Canada approved preventative oral medication, could reduce HIV acquisition in men who have sex with men by 44%, or as much as 99% with high adherence.
The model developed at St Michael’s suggests that over 20 years, PrEP use in 25, 50, 75 and 100% of the highest risk gay men would prevent 1,166, 2,154, 2,816 and 3,012 new HIV infections, and 70, 117, 137, and 140 HIV-associated deaths. The estimated cost of implementing PrEP would increase as more high-risk men used it, from $80m with 25% PrEP coverage to $270m with 100% PrEP coverage.
Putting gay men on preventative therapy could have the added benefit of bringing them into contact with the health care system, meaning they are more likely to be tested regularly for HIV and to have other health issues diagnosed and/or attended to, said one of the paper’s authors, Dr Darrell Tan, an infectious disease specialist who led a PrEP clinical trial at St Michael’s.
Tan and his colleagues found that although testing alone prevented fewer infections than use of PrEP, there was a reduction in cost to the health care system ($11,359 per infection prevented) by screening these high-risk patients regularly.
Tan said one thing that makes this study different is that it focuses exclusively on Toronto. Most models of PrEP’s clinical – and/or cost-effectiveness are based on national-level sexual behaviours and data. But Tan said a national perspective can ignore local or regional differences, whereas strong local data can be more persuasive in shaping local policy and programmes.
Of the estimated 57,400 gay men living in Toronto, nearly 20% have HIV. Despite the availability of anti-retroviral therapy drugs and sustained investments in behavioural prevention programmes, rates of newly diagnosed HIV infections and HIV-attributable deaths have not markedly declined in this demographic group in the last 10 years.
Finally, Tan said the growing evidence of PrEP’s clinical and cost effectiveness comes at a time when some provinces are considering whether to cover the expensive drug on publicly funded insurance plans. The drug now costs between $12,000 and $15,000 a year, meaning it is affordable only to people in clinical trials or with private insurance.
“This study makes a strong argument for public reimbursement of this drug,” said Tan. “It’s more evidence the drug is both clinically and cost effective when targeted at men at highest risk. A large benefit comes from engaging non-diagnosed HIV-infected men into care.”
Introduction: Once-daily tenofovir/emtricitabine-based pre-exposure prophylaxis (PrEP) can reduce HIV acquisition in men who have sex with men (MSM), by 44% in the iPrEx trial, and reaching up to 99% with high adherence. We examined the potential population-level impact and cost-effectiveness of different PrEP implementation strategies.
Methods: We developed a dynamic, stochastic compartmental model of HIV transmission among the estimated 57,400 MSM in Toronto, Canada. Parameterization was performed using local epidemiologic data. Strategies examined included (1) uniform PrEP delivery versus targeting the highest risk decile of MSM (with varying coverage proportions); (2) increasing PrEP efficacy as a surrogate of adherence (44% to 99%); and (3) varying HIV test frequency (once monthly to once yearly). Outcomes included HIV infections averted and the incremental cost ($CAD) per incremental quality-adjusted-life-year (QALY) gained over 20 years.
Results: Use of PrEP among all HIV-uninfected MSM at 25, 50, 75 and 100% coverage prevented 1970, 3427, 4317, and 4581 infections, respectively, with cost/QALY increasing from $500,000 to $800,000 CAD. Targeted PrEP for the highest risk MSM at 25, 50, 75 and 100% coverage prevented 1166, 2154, 2816, and 3012 infections, respectively, with cost/QALY ranging from $35,000 to $70,000 CAD. Maximizing PrEP efficacy, in a scenario of 25% coverage of high-risk MSM with PrEP, prevented 1540 infections with a cost/QALY of $15,000 CAD. HIV testing alone (Q3 months) averted 898 of infections with a cost savings of $4,000 CAD per QALY.
Conclusions: The optimal implementation strategy for PrEP over the next 20 years at this urban centre is to target high-risk MSM and to maximize efficacy by supporting PrEP adherence. A large health benefit of PrEP implementation could come from engaging undiagnosed HIV-infected individuals into care.
Derek R MacFadden, Darrell H Tan, Sharmistha Mishra