Department of Medicine, University of Cambridge, Addenbrookes Hospital, Cambridge, UK. Department of Infectious Disease, St Mary's Medical School, Imperial College London, London, UK. MRC-University of Glasgow Centre for Virus Research, University of Glasgow, Glasgow, UK. Cambridge Institute of Therapeutic Immunology & Infectious Disease (CITIID), Jeffrey Cheah Biomedical Centre, University of Cambridge, Cambridge, UK. MRC-University of Glasgow Centre for Virus Research, University of Glasgow, Glasgow, UK. david.l.robertson@glasgow.ac.uk. Department of Medicine, University of Cambridge, Addenbrookes Hospital, Cambridge, UK. alessandrocarabelli@gmail.com.