1. Oxford Vaccine Group, Department of Paediatrics, University of Oxford, Oxford OX3 7LE, UK
2. National Institute for Health Research (NIHR) Oxford Biomedical Research Centre, Oxford OX4 2PG, UK
3. Department of Clinical Research, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London WC1E 7HT, UK