1 Centre for Respiratory Disease and Meningitis, National Institute for Communicable Diseases, Johannesburg, South Africa.
2 School of Public Health and, Johannesburg, South Africa.
3 Medical Research Council: Respiratory and Meningeal Pathogens Research Unit, Johannesburg, South Africa.
4 National Research Foundation: Vaccine Preventable Diseases Unit, Faculty of Health Science, University of the Witwatersrand, Johannesburg, South Africa.