Impacts of US Bilateral Aid Disruptions on HIV Resurgence in Zambia: A Mathematical Modeling Study.

Background: Of countries with high HIV prevalence, Zambia had the largest proportion of funding to its HIV program from the United States President's Emergency Plan for AIDS Relief (PEPFAR)-84% at the start of 2025. Abrupt withdrawal of bilateral aid in January 2025 disrupted HIV services. This study aimed to estimate the health and epidemiological consequences of the disruptions, and to what extent impacts could be mitigated by restoring services.

Methods: We leveraged a previously developed HIV agent-based network transmission model, Epidemiological MODeling software for HIV, calibrated to Zambian HIV data at the provincial level. Health authorities leading the Zambian HIV program identified data and assumptions regarding impacts of aid disruptions by province and associated uncertainty ranges. We simulated disruptions lasting 3 months, 1 year, 4 years, or unabated, versus a counterfactual of no disruptions, over 2025-2060. Outcomes included additional HIV infections, deaths, and prevalence.

Results: Unabated disruptions added 3.3 million HIV acquisitions (8.8x more than no disruption) and 1.6 million HIV deaths (5.3x), with the largest number among women (1.5 million acquisitions, 790 933 deaths) and the largest proportional increase among children (21.6x acquisitions, 20.8x deaths). Restoring services within 3 months would limit additional acquisitions to 54 863 (+13.1%) and additional deaths to 32 550 (+8.7%). HIV prevalence would increase by 4.5x if disruptions were unabated through 2060, but would not change (0.0x) if services were restored within 3 months.

Conclusions: Rapid restoration of HIV services disrupted by the 2025 bilateral aid withdrawal could save >1.5 million lives and prevent epidemic resurgence in Zambia.