Group research description: We work on viral infections that are transmitted between humans and animals in Africa with a focus on vaccine development for their control. While many of these viruses were first discovered in Africa, very little is known regarding their distribution, associated disease burden and viral genetic diversity in the continent. We are leveraging our unique biobank, spanning more than 30 years, at the Programme in coastal Kenya to address these knowledge gaps. We expect data from these studies to inform target product profiles for candidate vaccines and underpin the design of clinical trials for vaccine efficacy estimation. Our vaccine programmes exploit synergies in human and livestock immunology to accelerate development of candidate vaccines for deployment in humans and the respective animal hosts of infection. Using this approach, we have developed ChAdOx1 RVF, a novel chimpanzee adenovirus vectored Rift Valley Fever vaccine, that is highly efficacious in multiple target livestock species (sheep, goats, cattle) and is currently in human phase I clinical trials (NCT04754776, NCT04672824). We have worked on a similar One Health vaccine for use against Middle East Respiratory Syndrome (MERS) in camels and humans, and our veterinary research programmes continue to inform advances in human vaccinology. We are at forefront of addressing the global shortage in Yellow Fever (YF) vaccine supply through conduct of multicentre clinical trials to evaluate the utility of fractional vaccine dosing for epidemic control. Findings from this work could have a major impact on the number of doses that can be given based on the current global stock of YF vaccine and the number of doses that are produced for future use. Our recent work on COVID-19 serology in Kenya has informed decisions on the national pandemic response and remains one of the most comprehensive COVID-19 seroepidemiological programmes in Africa to date.