BACKGROUND: HIV Prevention Trials Network (HPTN) 084 demonstrated superior efficacy of long-acting, injectable cabotegravir (CAB-LA) compared to daily oral tenofovir/emtricitabine (TDF-FTC) for HIV PrEP in cisgender women. We projected the drug cost at which CAB-LA would provide good value compared to TDF-FTC among adolescent girls and young women (AGYW) in South Africa.
METHODS: Using microsimulation modeling, we examined two PrEP strategies over 10 years among AGYW (ages 15-30y; scaled to n=10,000): TDF-FTC and CAB-LA. Published data informed model inputs, including: HIV incidence (TDF-FTC: 1.85/100 person-years, CAB-LA: 0.2/100 person-years; HIV transmissions off-PrEP from 10,000 AGYW to partners (16/year); and 2-year retention (TDF-FTC: 88%, CAB-LA: 85%). We assumed constant incidence and transmission risk over time. Annual costs included: PrEP drug+program (TDF-FTC: $77+$74, CAB-LA: $153+$75), ART ($58 to $834), and HIV-related care ($215 to $1,621). Model-projected outcomes include incident infections among and transmissions from AGYW, life-years (LYs), costs, incremental cost-effectiveness ratios (ICER=$/LY), and CAB-LA’s maximum price premium (MPP: the highest drug price at which CAB-LA would have an ICER below a willingness-to-pay [WTP] of 50% South Africa’s per-capita GDP [$3,500/LY]).
RESULTS: Per 10,000 AGYW in South Africa, projected infections and transmissions were higher and LYs lower in TDF-FTC (2,050 infections / 658 transmissions / 85,889 LYs), compared to CAB-LA (1,151 / 342 / 86,057) (Table). HIV infections avoided among male partners resulted in 143 LYs gained in CAB-LA over TDF-FTC. At $153/year drug cost, CAB-LA would exceed the WTP threshold (ICER=$6,600/LY). The projected MPP for CAB-LA to be cost-effective and cost-saving would be $136/year and $118/year, respectively. Accounting only for the benefits accruing to AGYW, the MPP to be cost-effective would be lower, $122/year. Varying transmissions from 2/year to 40/year would yield an MPP of $124-158/year to remain cost-effective.

Table. 10-year model-projected outcomes of CAB-LA versus TDF-FTC for HIV PrEP among adolescent girls and young women in South Africa, (n=10,000)
StrategyIncident infections in AGYW, nTransmissions to male partners, nDiscounted LYsDiscounted costs, USDICER ($/LY)*CAB-LA maximum price premium, USD
AGYWLYs gained from partners**AGYWCosts saved from partners**AGYWAllAGYWAll

Abbreviations: AGYW: adolescent girls and young women; CAB-LA: long-acting, injectable cabotegravir; ICER: incremental cost-effectiveness ratio; LY: life-year; PrEP: pre-exposure prophylaxis; TDF-FTC: tenofovir/emtricitabine; USD: United States Dollars.
*The ICER is the difference in cost divided by the difference in life expectancy for each strategy compared with the next less-costly strategy. Results are rounded to the nearest $100.
**Life-years gained and costs saved are among male partners in CAB-LA compared to TDF-FTC who, in the absence of the PrEP strategy being provided to AGYW, would have acquired HIV.
Life-years and costs are discounted at 3%/year and scaled to n=10,000 AGYW.

CONCLUSIONS: Among AGYW in South Africa, CAB-LA could reduce transmissions and increase life-years compared to TDF-FTC. CAB-LA should be priced at less than twice the cost of TDF-FTC to be cost-effective in South Africa.