Background High incidence rates of HIV, sexually transmitted infections (STIs) and teenage pregnancy are major challenges facing South Africa. The role of socio-economic factors in driving these is complex, with high socio-economic status protecting against some risk behaviours (condomless sex, early sexual debut and casual/transactional sex in females) but increasing other risk behaviours (e.g. male engagement in casual and commercial sex). Consequently, the impact of different economic strengthening interventions is unclear.

Methods We extended a previously-developed agent-based model of HIV, STIs and fertility in South Africa, to reflect effects of education, employment and per-capita household income on sexual behaviours. These effects were estimated from literature and from calibration of the model to African randomized controlled trials of economic strengthening interventions.

Population attributable fractions (PAFs) were calculated. We considered three intervention types, all targeting households with log per-capita income below the national average: school support to reduce school dropout; vocational training for unemployed adults; and unconditional cash transfers.

Results Low socio-economic status is estimated to have accounted for 14% of new HIV infections, 10% of incident STIs (gonorrhoea, chlamydia and trichomoniasis) and 46% of teenage births in South Africa, over 2000-2020. However, because of uncertainties regarding effect sizes, confidence intervals around these PAFs are wide (3-32%, 0-21% and 12-89% respectively), with uncertainty in the effect of education on condom use being the most significant correlate of the HIV PAF (r=0.94) and the relative rate of female sexual debut while in school being the most significant correlate of the teenage birth PAF (r=-0.96). Over 2025-2040, none of the interventions are estimated to have impacts significantly different from zero, due to limited impact on secondary economic outcomes. However, school support would come close to significantly reducing teenage births (by 4%, 95% CI: -1-18%).

Conclusions Although poverty is likely to be a significant driver of HIV, STIs and teenage pregnancy in South Africa, precise quantification is challenging. Recently trialled economic strengthening interventions have insufficient impact on socioeconomic status to reduce HIV and STIs significantly at a population level.

The authors have declared no competing interest.

Funded by the Gates Foundation, through the HIV Modelling Consortium (grant 007145).

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This modelling study makes use of estimates from published studies, which are cited in the paper and supplementary materials. The code is available from the corresponding author on request.