Other calculations in this report are based on estimates of the number of primary infections averted by NSPs; that is, associated with transmissions via sharing of syringes. These yield conservative estimates of the total number of infections averted, since secondary transmissions through other routes of exposure are not included. In this section an estimate of the number of secondary transmissions averted due to NSPs, from sexual contact or mother-to-child transmission, is calculated with a simple mathematical framework (see Appendix A). Although there is large heterogeneity between individuals, average behaviour is assumed in order to estimate the order of magnitude of the number of secondary cases averted. It is estimated that ~0.44 secondary HIV cases are due to each IDU-related HIV infection and ~0.11 secondary HCV cases from each primary HCV infection (Appendix A). The estimated total numbers of HIV and HCV infections averted (primary and secondary) due to different NSP coverage levels are shown in Table 3: median estimates are shown.

Table 3: Median estimates of primary and secondary HIV and HCV infections averted (2010-2019)

Cumulative number of infections averted (2010-2019) relative to no NSPsPrimary HIV infectionSecondary HIV infectionTotal HIV infectionPrimary HCV infectionSecondary HCV infectionTotal HCV infection
25% decrease in NSP coverage
17,900
7,876
25,777
68,104
7,491
75,596
10% decrease in NSP coverage
17,971
7,907
25,879
81,368
8,950
90,318
Current NSP coverage
18,008
7,923
25,931
87,789
9,657
97,445
10% increase in NSP coverage
18,025
7,931
25,956
95,455
10,500
105,955
25% increase in NSP coverage
18,051
7,943
25,994
103,915
11,431
115,345