He chairs the UK Department of Health’s Joint Committee on Vaccination and Immunisation and the European Medicines Agency scientific advisory group on vaccines and is a member of WHO’s SAGE. His research includes the design, development and clinical evaluation of vaccines including those for meningococcal disease and enteric fever and leads studies using a human challenge model of (para)typhoid. He has a particular interest in the development of B cell immunity in early childhood. He runs surveillance for invasive bacterial diseases and studies the impact of pneumococcal vaccines in children in Nepal. He also leads a project on burden and transmission of typhoid in Nepal, Bangladesh and Malawi, and trials of typhoid vaccines in South Asia. He has supervised 37 PhD students and his publications include over 500 manuscripts and books on various topics in paediatrics and infectious diseases.