1 Kenya Medical Research Institute, Nairobi, Kenya.
2 Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa.
3 World Health Organization Collaborating Centre for New Vaccines Surveillance, Medical Research Council Unit, at London School of Hygiene & Tropical Medicine, Banjul, The Gambia.
4 Division of Microbiology & Immunity, Warwick Medical School, University of Warwick, Warwick, United Kingdom.
5 Department of Pharmaceutical Microbiology, University of Ibadan, Ibadan, Nigeria.