1. Medical Research Council, Respiratory and Meningeal Pathogens Research Unit, Faculty of Health Science, University of the Witwatersrand, Johannesburg, South Africa
2. Department of Science/National Research Foundation, Vaccine Preventable Diseases, Faculty of Health Science, University of the Witwatersrand, Johannesburg, South Africa
3. Department of Pediatrics, University of Alabama School of Medicine, Birmingham
4. Department of Microbiology, University of Alabama School of Medicine, Birmingham