This report was commissioned by the UK Department of Health and Social Care to: Describe the current landscape of vaccine development against infectious diseases of epidemic potential (IDEPs), previously defined as ‘priority diseases’ by the UK Vaccine Network (UKVN); Consider lessons learnt from developing vaccines against Ebola and COVID-19; Review remaining technical gaps that might be targeted by future UKVN funding; and Propose optimal mechanisms for project funding to ensure value for money. UKVN was established following the 2014-16 Ebola outbreak in West Africa and used an expert panel to develop a list of priority pathogens which cause IDEPs and for which vaccines should be developed. This list covered 13 priority pathogens, including Disease X, any previously unknown pathogen capable of causing epidemic disease. There was recognition that excellent pre-clinical studies showing safety and immunogenicity of prototype vaccines in animals were not being translated into vaccines for use in humans. UKVN specifically aimed to progress vaccines for priority diseases through to early phase clinical trials so that they were available for scale up and emergency use in the event of future epidemics.