HIV Prevention Research: What Studies Show About PrEP, Testing, and Persistent Disparities

HIV prevention has been transformed over the past decade by the development and deployment of pre-exposure prophylaxis, a daily medication regimen that reduces HIV acquisition risk by more than 99 percent when taken consistently. Despite this remarkable pharmaceutical advance, HIV transmission rates in the United States have not declined at the rate that the availability of such an effective prevention tool would suggest, and significant disparities persist in both HIV incidence and access to prevention tools. Research on the implementation of PrEP, barriers to uptake in high-risk populations, and the structural factors that perpetuate HIV disparities is essential for developing public health responses that can close these gaps. PrEP was approved by the FDA in 2012, and research on its effectiveness in real-world settings has consistently confirmed the efficacy seen in clinical trials. Studies of PrEP use in diverse populations including gay and bisexual men, transgender women, people who inject drugs, and heterosexual individuals with HIV-positive partners find that consistent use produces near-complete protection against HIV acquisition. Research on PrEP adherence patterns finds that individuals who maintain daily adherence have very low rates of infection, while those who take PrEP inconsistently have lower levels of protection, underscoring the importance of adherence support alongside prescription. PrEP uptake has been substantially lower than public health projections suggested when the medication was approved. Research on PrEP awareness finds that a significant proportion of individuals at high risk for HIV either do not know about PrEP or do not perceive themselves as candidates for it. Provider prescribing of PrEP is lower than prevalence of eligible patients would suggest, driven by inadequate training, concerns about patient adherence, and discomfort with sexual health conversations. Research on prescribing patterns finds that primary care providers in high-prevalence areas prescribe PrEP at much lower rates than infectious disease specialists, representing a missed opportunity given that primary care is where most high-risk individuals receive healthcare. Racial and ethnic disparities in HIV incidence and PrEP uptake are stark and persistent. Black Americans account for a disproportionate share of new HIV diagnoses while receiving PrEP at much lower rates than white Americans. Research on these disparities finds that they reflect a combination of structural barriers including higher rates of poverty, less access to healthcare, higher rates of uninsurance, and residential segregation that concentrates risk in specific communities. Community-level factors including high rates of HIV among potential sexual partners, stigma around HIV testing and treatment, and distrust of the healthcare system all contribute to higher risk and lower prevention tool access in Black communities. Injectable PrEP, a long-acting form administered by injection every two months rather than as a daily pill, was approved by the FDA in 2021 and has shown comparable effectiveness to daily oral PrEP in clinical trials. Research on patient preferences for injectable versus oral PrEP finds that many individuals, including those who face daily adherence challenges, prefer injectable formulations. Long-acting injectable PrEP could overcome adherence barriers that limit the effectiveness of oral PrEP for some individuals, though implementation requires more frequent healthcare contact and cold chain distribution that creates implementation challenges. HIV testing is foundational to HIV prevention and treatment, as people who do not know their status cannot access treatment and may unknowingly transmit the virus. Research on HIV testing rates finds that a meaningful proportion of Americans who would be classified as high risk have never been tested, and that HIV testing rates are lower in communities with stigma around testing and HIV. Opt-out testing policies, which offer HIV testing to all patients in healthcare settings unless they actively decline, have increased testing rates in settings where they have been implemented. Research on opt-out testing finds that it reaches individuals who would not have sought testing on their own and that it identifies a significant proportion of previously undiagnosed HIV cases. Treatment as prevention is another important component of the contemporary HIV prevention paradigm. Research has established that people with HIV who achieve viral suppression through treatment are essentially unable to transmit the virus sexually. This U=U finding, meaning undetectable equals untransmittable, has transformed both clinical guidance and public health messaging. Research on the impact of broad access to treatment on HIV transmission rates at the population level finds that communities with high proportions of HIV-positive individuals engaged in care and achieving viral suppression have lower HIV incidence, supporting the public health case for expanded treatment access as a prevention strategy.