1. Centre for Respiratory Diseases and Meningitis, National Institute for Communicable Diseases of the National Health Laboratory Service, South Africa
2. School of Public Health, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
3. Influenza Division, Centers for Disease Control and Prevention, Atlanta, Georgia
4. Influenza Program, Centers for Disease Control and Prevention, Pretoria, South Africa
5. US Public Health Service, Rockville, Maryland
6. Department of Science and Technology/National Research Foundation: Vaccine Preventable Diseases, University of the Witwatersrand, Johannesburg, South Africa