Using data from IeDEA-SA cohorts, Cleophas’s PhD work will focus on antiretroviral drug resistance among patients failing protease inhibitor-based second-line treatment. HIV drug susceptibility for each participant will be predicted using the Stanford algorithm and will be categorized as susceptible, low level resistance, intermediate resistance, or high level resistance Furthermore, he will assess the factors associated with drug resistance mutations at second-line failure. He will evaluate early treatment response to third-line treatment focusing mainly on viral, immunological and clinical outcomes. Outcomes will be assessed at 24, 48 and 96 weeks post third-line commencement. He will assess the cost effectiveness of third-line treatment by extending our existing simulation model to compare different strategies after second-line ART failure similar to a previous modelling study done by Ouattara et al. Cleophas currently works as a Medical Officer at Newlands Clinic in Harare, Zimbabwe. Newlands Clinic is a private, not for profit organization run by Swiss AIDS Care International-Zimbabwe. The Clinic works in partnership with the Zimbabwe Ministry of Health and Child Care to provide comprehensive HIV treatment and Care to the vulnerable members of society at no cost to the patient.