Hepatitis C virus (HCV) is the most common chronic infectious agent among injecting drug users (IDUs); in many places IDUs are more likely to be infected than not. The enormous toll the virus wreaks in liver damage and hepatocellular cancer on its victims limits lives and tests the limits of the safety net systems that care disproportionately for this vulnerable group. Even as newer, more effective (and more costly) treatments become available, prevention probably remains the wiser course. Harm reduction programs such as opioid substitution therapy (OST) and needle and syringe exchange (NSP) hold that promise. New analyses of observational data from IDUs in the United Kingdom  suggest a 50% or greater reduction in odds of new HCV infection with OST and NSP, yet the reach of these programs varies by locality and in many places is still quite low. What could we gain by scaling-up these programs?
Vickerman and colleagues  have constructed a useful model to assess the impact of the scale-up of OST and NSP on HCV prevalence among populations of IDUs with different rates of chronic HCV infection. The United Kingdom has one of the best-developed OST and NSP efforts in the world, with up to 50% of users availing themselves of these resources. Using data from the recent meta-analysis, the authors estimate that OST and NSP initiatives have prevented a rise in chronic HCV prevalence to 65% from 40% in the United Kingdom, a substantial achievement. Up to 50 000 HCV infections among the 200 000 IDUs in England and Wales may have been averted over the last 20 years .
However, a little caution is warranted in interpreting these findings. First, estimates of the impact of OST and NST are based on pooled person-level data from approximately 1000 HCV negative IDUs enrolled in OST and/or NST programs in the United Kingdom since 2000 . While this may be the best available data to understand the impact of OST and NST in the United Kingdom, the UK experience may not reflect experiences in other countries. A recent review identified eight studies assessing the impact of OST on HCV outside the United Kingdom ; it would have been useful to incorporate these assessments of effectiveness into the model in sensitivity analysis or discuss estimates of effectiveness of OST and NST outside the United Kingdom to put the UK experience into context. Furthermore, although the authors of the pooled analysis concluded that data on OST were not heterogeneous , they used relatively liberal criteria for determining heterogeneity. A common and more conservative cut-off for determining heterogeneity (I2 > 25 or P < 0.01) would classify the results for OST as heterogeneous, warranting additional analyses to explore for sources of heterogeneity. Hence, additional data are needed to confirm the magnitude of effectiveness of OST and NSP and to conduct exploration of the heterogeneity suggested among OST interventions.
Despite these limitations in the data, Vickerman and colleagues usefully leverage the pooled UK evidence to explore the impact of scale-up of OST and NSP and have laid a foundation for future research and implementation of harm reduction programs for IDUs. For future scale-up, an understanding of the budget impact of these programs and modeling of the costs and effects of each program is needed urgently to help planners to tailor harm reduction programs to local needs and resources. For example, Zarin & Brandeau  used models to demonstrate that in settings of high HIV prevalence, approximately two-thirds of a harm reduction budget should be allocated to needle exchange programs and one-third to condom availability for IDUs, whereas in low-prevalence settings, 95% of the budget should be allocated to methadone maintenance for HIV infected IDU and the remainder of the budget to untargeted condom availability programs.
Additionally, complementary or alternative strategies are available to reduce harm among IDUs, such as education on the use of bleach to disinfect needles, condoms to prevent the spread of HIV and social programs to reduce homelessness, and should be considered in future models. In sensitivity analyses, Vickerman and colleagues identified high-risk injecting (associated with homelessness) as an important factor affecting the effectiveness of OST and NSP in decreasing HCV prevalence. Models that consider that consider a full menu of harm reduction interventions and consider the other benefits of harm reduction interventions in addition to reducing HCV prevalence (e.g. reducing HIV prevalence and drug-related crime) from an institutional or local government perspective would be particularly useful to public health leaders.
As public health departments increasingly face choices on how to spend scarce resources for prevention, information about the effectiveness of harm reduction strategies is particularly welcome. Future efforts to model the benefits and costs of harm reduction strategies can provide critical information to help public health planners allocate resources most effectively to reduce the harm associated with injecting drug use.
Declarations of interest