Toronto-led team explores different PrEP deployment scenarios

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Truvada is a pill containing the following two anti-HIV drugs:

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  • tenofovir DF – 300 mg
  • FTC (emtricitabine) – 200 mg

Health Canada has approved the daily use of Truvada to reduce the risk of sexual transmission of HIV as part of a series of prevention measures that includes the following:

  • testing for HIV prior to initiation of Truvada
  • screening for and, when necessary, treatment of sexually transmitted infections
  • regular and frequent testing for HIV while using Truvada
  • use of condoms

Health Canada based its approval on data from clinical trials involving men who have sex with men (MSM), as well as heterosexual couples where one partner was HIV positive. In these studies, Truvada was taken once daily in addition to the previously mentioned series of prevention measures. In this context, Truvada was highly effective at reducing the risk of HIV infection.

When HIV-negative people take medicines to reduce the risk of becoming infected with HIV, this is called pre-exposure prophylaxis (PrEP).

Thinking big

Now that Truvada is approved as part of a package of HIV prevention tools, some researchers are beginning to study how it might be deployed on a relatively large scale. Such studies are important to assess additional elements that may be needed to maximize the impact of PrEP, calculate the cost of such an intervention and estimate the impact of the large-scale deployment of PrEP on the course of the HIV epidemic. Cost figures will become important when discussions are held with health policy analysts and health departments about planning the large-scale deployment of PrEP.

Researchers at St. Michael’s Hospital in Toronto have developed computer simulations to study the possible impact that deploying  PrEP could have on the HIV epidemic in that city. Their model incorporated many factors, including rates of HIV infection over the past decade, deaths due to HIV, data from a sexual health clinic about sexual behaviours among MSM, and the effectiveness of PrEP in clinical trials. They programmed their simulations to project up to 20 years into the future. Their calculations, in press in the Journal of the International AIDS Society, suggest that “the optimal implementation strategy for PrEP over the next 20 years [in Toronto] is to [make it available to men who have high risk sex with other men] and to maximize [its effectiveness] by supporting PrEP adherence.” The research team also noted that “a large health benefit of PrEP implementation could come from engaging” MSM who are at high risk for this infection into regular HIV screening.

The Toronto context

According to the research team, 837 new HIV infections occurred in the province of Ontario in 2014, about half of which were in Toronto. Furthermore, previous research suggests that approximately 20% of MSM living in Toronto have HIV. Using data specific to Toronto, the team further estimates that nearly 29% of HIV-positive MSM living in Toronto do not know their infection status. Additional points of interest include the following: in the period from 2001 to 2011, between 330 and 400 MSM were diagnosed with HIV each year; also in that period, between 58 and 72 HIV-positive people died each year. All of these trends in infections and deaths helped to inform the researchers’ simulations.

The researchers developed a complex mathematical model that mimicked the spread of HIV in Toronto among MSM, as well as the impact of different degrees of PrEP deployment over a period of 20 years. They also calculated the cost of such interventions and the cost of HIV care. In all scenarios, PrEP was taken daily. All costs are expressed here in Canadian dollars.

Results

According to the researchers’ simulations, without large-scale deployment of PrEP over the next 20 years, the following would occur in Toronto:

  • 8,378 new HIV infections
  • 1,567 deaths related to HIV

The researchers examined several different scenarios, of which these are just a few:

  • If 25% of MSM who engage in high-risk sex were to be offered and use PrEP, this would be cost-effective, according to the researchers’ estimates. This finding is broadly similar to the results of similar analyses performed in Australia and the United States.
  • Increasing the frequency of HIV testing to once every month (vs. every three months as is currently recommended in U.S. PrEP guidelines) among PrEP users would have a “minimal” impact on preventing new infections. Instead, the researchers stated that it might be more useful to “focus efforts on PrEP adherence” given that clinical trials of PrEP have found greater effectiveness with better adherence.

Another potential benefit

According to the researchers, their simulations found a “potentially large collateral health benefit of PrEP programs.” This benefit would be realized by “engaging more high-risk MSM in routine HIV testing, even if they do not ultimately take PrEP.” Such engagement would occur because PrEP programs are relatively new. This novelty would offer “a new opportunity to engage these individuals in care by providing a means through which they may reduce their likelihood of infection, and potentially feel more comfortable with regular [HIV] screening.”

This focus on HIV screening is an important part of preparing to enter a PrEP program and an essential part of overall efforts to prevent the spread of HIV. The Public Health Agency of Canada estimates that about 21% of people who have HIV do not know their infection status. Keep in mind that this figure is an average for the entire country, and there are likely regions or cities where this figure is higher or lower. The researchers note that other studies have found that there are several common reasons that some MSM (and other populations) may avoid HIV testing, including the following:

  • belief that they may not be at risk for HIV
  • fear of a positive test result
  • fear that other people might find out that they are HIV-positive

An HIV prevention program centred on PrEP could help encourage people to come forward for HIV testing and engagement in risk reduction.

Costs of prevention and treatment

At present, Truvada costs about $1,000 per person per month in Canada. The researchers calculated that if 25% of MSM at highest risk for HIV were offered and accepted PrEP, the cost would be around $80 million over 20 years. If 100% of MSM at highest risk for HIV were offered and accepted PrEP, the cost over 20 years would rise to approximately $269 million. Bear in mind that these estimates are very conservative. Generic versions of tablets containing tenofovir and FTC may become available in Canada in a few years. Such generic versions would be much cheaper, and the cost of deploying PrEP on a large scale would likely fall substantially.

Another important factor that should be taken into account is that the life-time costs of care and treatment for HIV would be avoided because, thanks to PrEP, many men would not become infected with HIV. In this regard, researchers in Quebec recently calculated that the average direct costs of one year of HIV treatment ranged from $16,000 to $24,000. Indirect costs were about $11,500 per person per year. Thus, total costs in the first year of HIV treatment would range between $27,000 and $35,000. The Quebec researchers found that PrEP taken “on demand” (before and after possible sexual exposure to HIV) was cost effective.

The Toronto researchers note that further refinements to their simulations are needed. For instance, they cite results from a clinical trial called IPERGAY suggesting that PrEP on demand was linked to an 86% reduction in the risk of HIV transmission. The researchers stated that “future work should assess how best to utilize daily and intermittent PrEP strategies from both a preventive efficacy and cost-effectiveness perspective [in the context of Toronto’s HIV epidemic].”

The Toronto-led team’s report is a good first step towards assessing the cost-effectiveness of PrEP at a local level, taking into account local trends in the HIV epidemic among MSM. These and other studies will be very useful in helping to guide the implementation of PrEP in the years ahead.

Acknowledgement

We thank infectious disease specialist Derek MacFadden MD, Harvard University, for helpful discussion, research assistance and expert review.

Resources

Pre-exposure prophylaxis (PrEP) – CATIE fact sheet

Pre-exposure prophylaxis (PrEP) resources

 —Sean R. Hosein

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