1 Bloomsbury Institute of Intensive Care Medicine, Division of Medicine, University College London, London WC1E 6BT, UK. Electronic address: m.singer@ucl.ac.uk.
2 Department of Acute Medicine, Royal Hampshire County Hospital, Hampshire Hospitals NHS Foundation Trust, Winchester, UK; NHS England, UK.
3 Department of Intensive Care Medicine, Guy's and St Thomas' NHS Foundation Trust, London, UK; Peter Gorer Department of Immunobiology, King's College London, London, UK.