Hepatitis C virus (HCV) is a major global public health concern, with approximately 114.9 (91.9-148.7) million people having antibodies to HCV, 3-4 million people newly infected each year and 350,000 deaths occurring annually. People who inject drugs (PWID) are the key at risk group in most high income countries and in most countries over half of PWID have been infected with HCV.

Evidence shows that injecting with needle/syringes previously used by someone else is the main risk factor for infection with HIV and HCV among PWID. Additional risks for HCV acquisition in this population include sharing drug preparation containers, filters, rinse water and backloading (a method of sharing drugs by transferring them from the needle of one syringe into the barrel of another). The provision of sterile injecting equipment through needle and syringe programmes (NSP) and enrolment in opioid substitution treatment (OST) are among the primary interventions for reducing HCV and HIV transmission among PWID. NSPs provide sterile needles/syringes and other injecting equipment to PWID, via fixed-sites, outreach, peer networks, vending machines, and pharmacies. By maximising the amount of sterile injecting equipment (including syringes, cookers, cottons) in circulation, the time infected equipment remains in circulation decreases and the proportion of unsafe injections or the need to share equipment to prepare drugs reduces. OST is prescribed to dependent opioid users to diminish the use and effects of illicitly acquired opioids and reduce the frequency of injection and exposure to unsafe injecting practices. The most commonly prescribed forms of OST are opiate agonist treatments - methadone maintenance therapy and buprenorphine maintenance treatment. NSPs and OST are often the first point of service contact for PWID and so they provide referrals and support to other social and welfare services.

There is good evidence that NSP and OST in combination reduce injecting risk behaviours and some evidence of an impact on HIV incidence. However, evidence for their impact on HCV incidence among PWID is limited.Recent reviews have estimated a moderate effect of NSPs in reducing HIV transmission by 48% (95% confidence interval (CI) 3-72%) and strong evidence for OST reducing HIV transmission by 54% (95% CI 33-68%). Previous evidence syntheses for use of NSPs has focussed primarily on HIV as the main outcome and, as a consequence, failed to include all the available evidence on HCV. Another review that measured the effect of NSP use did not include a metaanalysis due to heterogeneity in the measurement of NSP exposure and focussed on evidence from North America, limiting the generalisability of findings to othersettings including Europe.  An analysis of pooled data examined the effect of NSP coverage on HCV incidence showed that high coverage of NSP (≥100% of injections with a sterile syringe) or receipt of OST either currently or within the past 6 months can each reduce HCV infection risk by 50%; and in combination by 80%. The small number of incident HCV cases meant that the efficacy estimate for 100% NSP among those not on OST was weak.