Hassan worked with the HIV/STI studies group based at the KEMRI/Wellcome Trust Research Programme in Kilifi, Kenya with an interest in understanding HIV-host interactions and their contribution to disease pathogenesis. To do this, he used samples from well-characterised cohorts from Kenya, Uganda, Rwanda, Zambia, South Africa and Sweden, effectively covering the most common circulating global subtypes. He aimed to characterise the virus using single genome sequencing and profile innate immune responses by multiplexing. He then used advanced multi-dimensional phylogenetic models to elucidate the interactions between the virus and the host, and how these contribute to acute retroviral syndrome and their subsequent effects on disease progression through to the chronic phase. It is envisaged that work from his project may have implications for prophylactic and therapeutic vaccine design.