1. Department of Infectious Disease Epidemiology, Imperial College London, St Mary's Hospital, Norfolk Place, London W2 1PG, UK
2. The Wellcome Trust Research Laboratory, Division of Gastrointestinal Sciences, Christian Medical College, Vellore, Tamil Nadu 632004, India
3. Department of Medicine, Imperial College London, St Mary's Hospital, Norfolk Place, London W2 1PG, UK
4. Vaccinology Theme, MRC Unit, The Gambia, Atlantic Road, Fajara, The Gambia