Professor Brown is an academic respiratory consultant at University College London where he leads a team investigating the pathogenesis and mechanisms of immunity for the bacterial causes of pneumonia Streptococcus pneumoniae and Acinetobacter baumannii, including the development of novel vaccine approaches. He has investigated phenotypic differences between S. pneumoniae and its closest genetic relative Streptococcus mitis to try and understand why S. pneumoniae is a frequent cause of severe infections whereas S. mitis is a relatively rare cause of significant infections in humans. His clinical practice concentrates on clinical respiratory infection, including bronchiectasis, aspergillosis, and pneumonia in immunocompetent and immunocompromised patients. He is a member of the UK Joint Committee on Vaccination and Immunisation, contributing to national decisions on vaccine policy including the COVID-19, influenza, and S. pneumoniae vaccination programme.