Estimating efficacy of tenofovir disoproxil fumarate and emtricitabine for HIV prevention in cisgender women with partial adherence.

Pre-exposure prophylaxis (PrEP) with daily oral tenofovir disoproxil fumarate and emtricitabine (TDF/FTC) is effective for HIV prevention. The adherence-efficacy relationship in men and transgender women who have sex with men (MSM/TGW) has been established by measuring tenofovir diphosphate concentrations (TFV-DP) in cases and controls. We calculate this adherence-efficacy curve for cisgender women using HIV incidence and plasma tenofovir concentrations from three trials (FEMPrEP, VOICE, and Partners PrEP). We impute TFV-DP concentrations from plasma tenofovir quantification using data from HIV Prevention Trials Network 082, which collected both adherence measures. We estimate two, four, or seven pills per week is associated with reductions in HIV incidence of 59% (95% credible interval 30% - 96%), 84% (95% CI: 52% - 100%), and 96% (95% CI: 73% - 100%), respectively. High adherence confers high protection in cisgender women, similar to MSM/TGW, and partial adherence confers only slightly lower protection.