Project Summary The elimination of HIV transmission with virally-suppressive antiretroviral therapy (ART) has provided the world with a clear path to end the HIV epidemic through the provision of ART at HIV diagnosis. Undetectable HIV is untransmittable (U=U). However we found limited knowledge of U=U among lay people in South Africa. The U=U campaign was launched in 2016 to disseminate the scientific evidence that people with HIV cannot transmit the virus if their viral load is undetectable. U=U has been endorsed by NIH, CDC, Pepfar, and organizations in over 100 countries. U=U has been shown to reduce stigma, improve quality of life for people living with HIV, and increase HIV testing. However, there is a critical need for evidence on (a) how best to disseminate information on U=U, and (b) the impact of U=U on ART adherence and viral suppression. With support from an NIH R34, we developed and piloted the “Undetectable & You” App, an educational U=U intervention designed as a support tool for HIV counseling in South Africa. The App was “co-created” with PLHIV and health providers and features the stories of PLHIV and their partners alongside the science of U=U. In this R01, we will (Aim 1) refine the App based on lessons learned from our pilot; and (Aim 2) establish the impact of the App on viral suppression in a cluster-randomized efficacy trial. We will collect outcomes data through a prospective survey sample (n=880) as well as through the National Health Laboratory Service (NHLS) National HIV Cohort (which we previously developed with NHLS), which offers a platform for evaluation using fully de-identified data. We will assess impacts on viral suppression (primary outcome) as well as ART visit adherence, retention in care, knowledge, attitudes, and mental health; and incident STIs and pregnancies. The study builds on a longstanding collaboration between the PIs (Dr. Jacob Bor, Dr. Dorina Onoya) and between Boston University and the Health Economics and Epidemiology Research Office (HE2RO) at the University of Witwatersrand in South Africa. The study will be implemented in close collaboration with South Africa’s National Department of Health (HIV Cluster) and Anova Health. This study is highly innovative because we take a novel approach – disseminating information on the prevention benefits of ART – to improve wellbeing of PLHIV and to motivate ART adherence leading to viral suppression. The research will have significant public health impact as the findings have potential to shape HIV counseling guidelines and U=U dissemination in the country with the world’s largest HIV epidemic.