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 NSPs||Primary HIV infection||Secondary HIV infection||Total HIV infection||Primary HCV infection||Secondary HCV infection||Total HCV infection|
|25% decrease in NSP coverage|
|10% decrease in NSP coverage|
|Current NSP coverage|
|10% increase in NSP coverage|
|25% increase in NSP coverage|