Modelling the impact of a national scale-up of interventions on hepatitis C virus transmission among people who inject drugs in Scotland

Background and Aims: To reduce hepatitis C virus (HCV) transmission among people who inject drugs (PWID), Scottish Government‐funded national strategies, launched in 2008, promoted scaling‐up opioid substitution therapy (OST) and needle and syringe provision (NSP), with some increases in HCV treatment. We test whether observed decreases in HCV incidence post‐2008 can be attributed to this intervention scale‐up. Design: A dynamic HCV transmission model among PWID incorporating intervention scale‐up and observed decreases in behavioural risk, calibrated to Scottish HCV prevalence and incidence data for 2008/09. Setting: Scotland, UK. Participants: PWID. Measurements: Model projections from 2008 to 2015 were compared with data to test whether they were consistent with observed decreases in HCV incidence among PWID while incorporating the observed intervention scale‐up, and to determine the impact of scaling‐up interventions on incidence. Findings: Without fitting to epidemiological data post‐2008/09, the model incorporating observed intervention scale‐up agreed with observed decreases in HCV incidence among PWID between 2008 and 2015, suggesting that HCV incidence decreased by 61.3% [95% credibility interval (CrI) = 45.1–75.3%] from 14.2/100 person‐years (py) (9.0–20.7) to 5.5/100 py (2.9–9.2). On average, each model fit lay within 84% (10.1/12) of the confidence bounds for the 12 incidence data points against which the model was compared. We estimate that scale‐up of interventions (OST + NSP + HCV treatment) and decreases in high‐risk behaviour from 2008 to 2015 resulted in a 33.9% (23.8–44.6%) decrease in incidence, with the remainder [27.4% (17.6–37.0%)] explained by historical changes in OST + NSP coverage and risk pre‐2008. Projections suggest that scaling‐up of all interventions post‐2008 averted 1492 (657–2646) infections over 7 years, with 1016 (308–1996), 404 (150–836) and 72 (27–137) due to scale‐up of OST + NSP, decreases in high‐risk behaviour and HCV treatment, respectively. Conclusions: Most of the decline in hepatitis C virus (HCV) incidence in Scotland between 2008 and 2015 appears to be attributable to intervention scale‐up (opioid substitution therapy and needle and syringe provision) due to government strategies on HCV and drugs.