Change in HIV Incidence, Prevalence and Population Viremia in Tanzania: Findings from Tanzania HIV Impact Surveys in 2016–2017 and 2022–2023

Background: Tanzania has over 1.5 million people living with HIV. Understanding changes in its HIV epidemic is critical to informing interventions and policies. We aim to describe the state of Tanzania’s HIV epidemic and progress towards epidemic control by evaluating changes in population-level HIV prevalence, HIV incidence, and viremia between 2016–2017 and 2022–2023. &nbsp; <br><br>Methods: Sequential Tanzania HIV Impact Surveys (THIS) 2016–2017 and 2022–2023 were nationally-representative, cross-sectional household-based surveys with a stratified, two-stage cluster design. Participants aged ≥15 years provided information on HIV testing and treatment histories and blood samples for HIV serology. HIV incidence was estimated using a laboratory-based algorithm (HIV-1 Limiting Antigen (Lag) avidity, viral load (VL), and antiretroviral (ARV) detection). We calculated weighted estimates of population-level HIV prevalence, HIV incidence, and viremia and compared them between surveys. Arithmetic differences and incidence rate ratios were used to assess change. Modified Poisson regression models were used to estimate adjusted prevalence ratios (aPR) for correlates of HIV prevalence and viremia. &nbsp; <br><br>Findings: Among participants aged ≥15 years with biomarker data (n=31,579 in 2016–2017; n=33,663 in 2022–2023), 1,831 and 1,850 were living with HIV, respectively. HIV prevalence remained stable at 4.9% [95% CI: 4.5–5.2] in 2016–2017 and 4.4% [4.1–4.7] in 2022–2023. Annual HIV incidence did not significantly change (0.24% [0.15–0.34] vs. 0.18% [0.09–0.26]). Population viremia declined significantly from 2.8% [2.6–3.1] to 1.7% [1.5–1.8], with a 41% reduction between surveys (aPR: 0.59 [0.52–0.67]). Higher prevalence and viremia were observed among women and adults aged ≥25 years. &nbsp; <br><br>Interpretation: Between 2016–2017 and 2022–2023, HIV prevalence and incidence remained stable in Tanzania, while population viremia declined substantially, indicating progress towards HIV epidemic control. Continued efforts and targeted interventions are needed to reduce viremia among women and older age groups.