OBJECTIVES To estimate and compare the costs and benefits of introducing a prison needle and syringe program in all Australian prisons.

STUDY DESIGN Stochastic compartmental modelling study.

SETTING All Australian prisons, 1 January 2010 to 31 December 2030.

INTERVENTION Introduction of a prison needle and syringe program in all Australian prisons during 1 January 2025 - 1 January 2027, with the aim of covering 50% of people who inject drugs in prison by 1 January 2030.

MAIN OUTCOME MEASURES Projected new hepatitis C virus (HCV) infections and hospitalisations with injection-related bacterial and fungal infections in prisons, with and without the needle and syringe program; costs of the program; savings in treatment costs for HCV and injection-related bacterial and fungal infections; benefit-cost ratio of the program.

RESULTS In the base scenario (no prison needle and syringe program), the projected number of new HCV infections during 2025-2030 was 2932 (uncertainty interval [UI], 2394-3507) and the projected number of hospitalisations with injection-related bacterial and fungal infections was 3110 (UI, 2596-3654). With the prison needle and syringe program, it was projected that 894 (UI 880-912) new HCV infections (30%; UI, 26-37%) and 522 (UI, 509-532) hospitalisations with injection-related bacterial and fungal infections (17%; UI, 15-20%) would be averted; the incidence of new HCV infections would be reduced from 3.1 (UI, 2.5-3.7) to 1.3 (UI, 1.0-1.7) per 100 person-years among people who inject drugs in prison. The estimated cost of the program was $12.2 million (UI, $7.6-22.2 million), and the saved care costs for HCV and injection-related infections were $31.7 million (UI, $29.3-34.6 million), yielding a benefit-cost ratio of 2.6 (UI, 1.4-4.1). The benefit-cost ratio was also greater than one for scenarios in which the assumptions and base values for several parameters were varied.

CONCLUSIONS Each dollar spent on a needle and syringe program in Australian prisons could save $2.60 in treatment costs for HCV and other injection-related infections.