1. Department of Infection & Immunity; Imperial College Healthcare NHS Trust; London W6 8RF United Kingdom
2. NW London Health Protection Unit; Health Protection Agency; London NW9 5EQ United Kingdom
3. Virus Reference Department; Microbiology Services Colindale; London NW9 5EQ United Kingdom
4. Centre for Immunity; Infection and Evolution, King's Buildings, University of Edinburgh; Edinburgh EH25 9RG Scotland United Kingdom
5. Occupational Health Department; Imperial College Healthcare NHS Trust; London W12 0HS United Kingdom
6. Department of Infectious Diseases; Imperial College; London W12 0HS United Kingdom