The reduction in new hepatitis C virus (HCV) infections that has taken place in Scotland since 2008 is most likely due to increased provision of needle and syringe programmes and opioid substitution therapy, rather than a reduction in the number of people with hepatitis C as a result of increased treatment of HCV infection, a modelling study published in the journal Addiction reports.
Scotland launched a national action plan for HCV and a national drug and alcohol strategy in 2008, which led to expanded coverage of needle and syringe programmes and opioid substitution therapy. New HCV infections fell by approximately 50% between 2008 and 2015 in Scotland. The vast majority of new infections in Scotland occur as a result of sharing injecting equipment, so it is plausible that reducing the sharing of injecting equipment, by scaling up service provision and the number of people reached with clean equipment, could have an impact on new infections.
Until now, however, there has been little evidence to show the extent to which new HCV infections might be reduced by harm reduction measures and little opportunity to validate models of the HCV epidemic against robust epidemiological data.
Researchers from the University of Bristol and three Scottish universities developed a model of the Scottish HCV epidemic to test the impact of varying levels of harm reduction provision. They assessed the robustness of the model by matching it against data on HIV incidence derived from Scotland’s Needle Exchange Surveillance Initiative.
The model took into account how many people were injecting drugs in Scotland, how long they had been doing so, whether they had HCV and when they became infected. People were removed from the model to simulate the death rates among injectors and former injectors.
Three interventions were included in the model: opioid substitution therapy (OST), needle and syringe programmes (NSP) and HCV treatment. Data from a UK systematic review were used to calculate the degree to which OST and NSP reduced the individual risk of HCV acquisition.
Modelling the Scottish HCV epidemic and interventions introduced after 2008 led the researchers to estimate that HCV incidence among current drug injectors fell by 61% between 2008 and 2015. The incidence of HCV projected in the model is within 84% of the actual HCV incidence measured by the Needle Exchange Surveillance Initiative, suggesting that the model performs well in representing the dynamics of the HCV epidemic in Scotland.
The model examined the effect of scaling up OST and NSP after 2008 by looking at what would have happened without the increased scale of activity. The model found that even without these interventions, the incidence would still have declined by 27%. But the interventions reduced HCV incidence further, and averted an estimated 1492 infections. Two-thirds of the infections were averted as a result of the increased provision of NSP and OST. Most of the remainder were likely to have been averted by a reduction in the number of high-risk injectors – those injecting stimulants or homeless – and less than 5% by treatment of HCV.
The findings give an indication of the potential impact on HIV incidence of scaling up harm reduction measures. Scale up of harm reduction could contribute to the more rapid achievement of hepatitis C elimination targets in settings where the vast majority of new HCV infections are a consequence of sharing injecting equipment.
“The study illustrates how a country-level HCV action plan incorporating the scale-up of a range of HCV prevention interventions can markedly reduce HCV incidence,” the authors conclude. “However, even with high OST and NSP coverage, the impact achieved in Scotland still falls short of the World Health Organization’s strategy for reducing HCV incidence by 90%.”
The authors say that further work is needed to assess how wider access to HCV treatment, together with OST in prisons, use of low dead-space syringes or safe injecting facilities might affect HCV incidence.
Fraser H et al. Modelling the impact of a national scale-up of interventions on hepatitis C virus transmission among people who inject drugs in Scotland. Addiction, advance online publication, June 2018, doi: 10.1111/add.14267