Modeling Highlights the Challenge of Achieving and Maintaining Hepatitis C Virus Micro-Elimination Among People Who Inject Drugs.

Background: People who inject drugs (PWIDs) are at high risk for acquiring and transmitting hepatitis C virus (HCV). Direct-acting antiviral (DAA) therapy leads to high cure rates. However, lack of protective immunity after cure and high re-infection rates in PWID necessitates access to multiple DAA treatments per PWID to reach the World Health Organization HCV elimination goal of 90% incidence reduction. A major public health challenge is determining the proportion of PWID to treat to reach the goal and the continued treatment levels required to maintain decreased incidence. Method: We used an agent-based model to study varying levels of DAA treatment among HCV-infected PWID from Chicago, IL, and the effects of reducing DAA treatment after elimination is reached. The model uses individual temporal viral load profiles to determine transmission probabilities relative to the HCV RNA titers of receptive syringe-sharing PWID. Results: Modeling predicts that insufficient DAA treatment can result in a continuous increase of HCV incidence over a 25-year period, with no significant decrease. Elimination can be achieved within 10 years with sufficient treatment levels. However, when DAA treatment is stopped, rates of new chronic HCV infections rapidly increase, returning to preelimination levels within 5 years. Annual treatment of ≥0.5% would maintain the elimination goal, but identifying and treating small numbers of infected people annually in PWID populations would be resource intensive. Conclusions: The challenge to achieve and maintain the elimination goal underscores the importance of augmenting DAA treatment with intervention strategies such as syringe service programs and vaccines.