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PrEP adherence is associated with periods of HIV risk among adolescent girls and young women in South Africa and Zimbabwe

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BACKGROUND: HIV pre-exposure prophylaxis (PrEP) uptake is increasing among adolescent girls and young women (AGYW) but adherence remains a challenge. There has been limited consideration of dynamic changes in AGYW's HIV risk which could impact PrEP decision-making over time. Understanding PrEP use during periods of HIV risk ('prevention-effective adherence') is critical to support PrEP adherence among AGYW.
METHODS: HPTN 082 was an open-label PrEP study among AGYW (ages 16-24) in South Africa and Zimbabwe from 2016-2018. PrEP adherence was measured at Weeks 13, 26, and 52 via tenofovir (TFV)-diphosphate (DP) in dried blood spots and TFV in plasma. Behavioral and STI data were collected quarterly. We categorized visits into a binary 'any HIV risk' variable, defined by South African and Zimbabwean PrEP guidelines (condomless sex, partner with HIV not taking antiretrovirals, partner with unknown HIV status, '¥1 partner, STI, transactional sex, drug/alcohol use around sex). We used generalized estimating equations to estimate longitudinal associations between any HIV risk and detectable TFV-DP. We also estimated associations between any risk and high PrEP adherence (intracellular TFV-DP '¥700 fmol/punch; plasma TFV '¥40 ng/mL). We explored the relationship between number of risk factors and continuous TFV-DP with linear models.
RESULTS: Among 398 AGYW, 85.4% reported '¥1 HIV risk factor at enrollment. 60.3%, 65.1%, and 64.3% reported '¥1 risk factor at Weeks 13, 26, and 52, respectively. Any HIV risk was associated with greater likelihood of detectable TFV-DP (adjusted relative risk [aRR]:1.15; 95% confidence interval [95% CI]: 1.03-1.29). Similar associations were observed with TFV-DP '¥700 fmol/punch (aRR:1.57; 95% CI: 1.09-2.25), and TFV '¥40 ng/mL (aRR:1.36; 95% CI: 1.11-1.65). Compared to visits when no risk factors were reported, those with 1 risk factor had TFV-DP levels 54.0 fmol/punch higher, those with 2 risk factors had TFV-DP levels 94.5 fmol/punch higher, and those with '¥3 risk factors had TFV-DP levels 223 fmol/punch higher (p-value<0.001).
CONCLUSIONS: The strong association between HIV risk and PrEP adherence among African AGYW indicates that participants were able to assess their risk and use PrEP effectively during periods of risk. These findings support the concept of prevention-effective PrEP adherence during 'seasons' of risk.