Author information: (1)Department of Medicine, University of Cambridge, Addenbrookes Hospital, Cambridge, UK. (2)Department of Infectious Disease, St Mary's Medical School, Imperial College London, London, UK. (3)Division of Infection and Immunity, University College London, London, UK. (4)MRC-University of Glasgow Centre for Virus Research, University of Glasgow, Glasgow, UK. (5)Roslin Institute, University of Edinburgh, Edinburgh, UK. (6)Department of Infection, Immunity and Cardiovascular Disease, Medical School, University of Sheffield, Sheffield, UK. (7)MRC-University of Glasgow Centre for Virus Research, University of Glasgow, Glasgow, UK. david.l.robertson@glasgow.ac.uk. (#)Contributed equally