1 The Vaccine Centre, London School of Hygiene & Tropical Medicine, London WC1 7HT, UK; Vaccines and Immunity Theme, Medical Research Council Unit The Gambia at London School of Hygiene & Tropical Medicine, Banjul, The Gambia.
2 Department of Primary Care and Public Health, Imperial College London, London, UK.
3 The Vaccine Centre, London School of Hygiene & Tropical Medicine, London WC1 7HT, UK; Vaccines and Immunity Theme, Medical Research Council Unit The Gambia at London School of Hygiene & Tropical Medicine, Banjul, The Gambia. Electronic address: beate.kampmann@lshtm.ac.uk.