London School of Hygiene & Tropical Medicine - Department of Clinical Research, University of North Carolina Project-China, London School of Hygiene & Tropical Medicine - Department of Clinical Research, The University of Hong Kong, Alfred Health - Melbourne Sexual Health Centre, University of Sheffield, Duke University, New York University (NYU), London School of Hygiene & Tropical Medicine - Department of Infectious Disease Epidemiology, London School of Hygiene & Tropical Medicine - Faculty of Public Health and Policy, London School of Hygiene & Tropical Medicine - Department of Infectious Disease Epidemiology, Gates Foundation - Beijing Representative Office, Peking University - Institute of Population Research, University of North Carolina (UNC) at Chapel Hill - Project-China, University of North Carolina Project-China, Jinan University, Zhuhai Center for Disease Control and Prevention, Guangdong Second Provincial General Hospital, Yangshan Health Centre - Vaccination Clinic, Fenghuang Community Health Service Centre, Xinhua Community Health Service Centre, Community Representative, Guangzhou, China, Guangdong Second Provincial General Hospital, Southern Medical University - Dermatology Hospital and Southern Medical University