1. Department of Infectious Disease Epidemiology, London School of Hygiene and Tropical Medicine, London, UK
2. Centre for the Mathematical Modelling of Infectious Disease, London School of Hygiene and Tropical Medicine, London, UK
3. Division of Viral Diseases, Centers for Disease Control and Prevention, Atlanta, GA, USA
4. Division of Healthcare Quality Promotion, Centers for Disease Control and Prevention, Atlanta, GA, USA