HCV elimination among people who inject drugs. Modelling pre- and post-WHO elimination era

Abstract

Background: Elimination of hepatitis C virus (HCV) among people who inject drugs (PWID) is a costly investment, so strategies should not only focus on eliminating the disease, but also on preventing disease resurgence. The aims of this study are to compute the minimum necessary antiviral therapies to achieve elimination with and without the additional expansion of harm reduction (HR) programs and to examine the sustainability of HCV elimination after 2030 if treatment is discontinued.

Method: We considered two types of epidemic (with low (30%) and high (50%) proportion of PWID who engage in sharing equipment (sharers)) within three baseline chronic HCV (CHC) prevalence settings (30%, 45% and 60%), assuming a baseline HR coverage of 40%. We define sustainable elimination strategies, those that could maintain eliminations results for a decade (2031-2040), in the absence of additional treatment.

Results: The model shows that the optimum elimination strategy is dependent on risk sharing behavior of the examined population. The necessary annual treatment coverage to achieve HCV elimination under 45% baseline CHC prevalence, without the simultaneous expansion of HR programs, ranges between 4.7-5.1%. Similarly, under 60% baseline CHC prevalence the needed treatment coverage varies from 9.0-10.5%. Increasing HR coverage from 40% to 75%, reduces the required treatment coverage by 6.5-9.8% and 11.0-15.0% under 45% or 60% CHC prevalence, respectively. In settings with ≤45% baseline CHC prevalence, expanding HR to 75% could prevent the disease from rebounding after elimination, irrespective of the type of the epidemic. In high chronic HCV prevalence, counseling interventions to reduce sharing are also needed to maintain the HCV incident cases in low levels.

Conclusions: Harm reduction strategies have a vital role in HCV elimination strategy, as they reduce the required number of treatments to eliminate HCV and they provide sustainability after the elimination. The above underlines that HCV elimination strategies should be built upon the existing HR services, and argue for HR expansion in countries without services.

Fig 1

Schematic outline of the mathematical model for HCV disease transmission and treatment states (A) and behavioral states (B). Parameters: θ represent the new injectors flow rate for sharers and non-sharers, λ_i the infection rate per year i which depends on people who inject drugs (PWID) status (whether they participate in a harm reduction programs), C the proportion that spontaneously clears the infection, Τ the annual treatment rate, ω the proportion of PWID achieving sustained viral response, μ₁ (mortality in the population of PWID), μ₂ (rate of leaving PWID population due to injecting cessation).

Fig 2. The needed treatment rate coverage (%) to achieve HCV elimination among PWID by 2030 under a in settings with 45% or 60% chronic hepatitis C prevalence.

The bars correspond to scenarios of harm reduction coverage at 40% and 75%. A. 45% CHC prevalence B. 60% CHC prevalence.

Fig 3. Model predictions assuming 60% chronic HCV prevalence and 30% or 50% of the people who inject drugs sharing injection equipment.

We assumed that no treatment is provided after 2030.Mean time of HCV acquisition greater than 25 years is shown as 24+ years. Mean time corresponds to Tx only scenario. Tx: Antiviral treatment, HR: harm reduction, Counselling: Psychological interventions to reduce re-infections post- treatment. A. 30% sharers-Prevalence B. 30% sharers-HCV Incident cases C. 50% sharers-Prevalence D. 50% sharers-HCV Incident cases.

Fig 4. Results of one-way sensitivity analysis showing the relative difference in needed treatment to achieve HCV elimination goals for varying parameters of the model compared to the base parameter values in Table 1.

A value of zero describes no change from estimated needed treatments compared to the base scenario. A positive or a negative value means that the required treatments are higher or lower to the estimated under the base scenario. The scenario of 45% chronic hepatitis C prevalence with 50% sharers was used.