Abstract
1 Defence Science and Technology Laboratory, Porton Down, Salisbury SP4 0JQ, UK
2 Swedish Defence Research Agency, SE-901 82 Umeå, Sweden
3 Department of Infection, Immunity and Inflammation, Maurice Shock Building, University of Leicester, PO Box 138, Leicester LE1 9HN, UK
4 Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, UK