Radcliffe Department of Medicine, University of Oxford, Oxford, UK; Adult Intensive Care Unit, Oxford University Hospitals NHS Foundation Trust, Oxford, UK. Electronic address: akshay.shah@linacre.ox.ac.uk. Oxford Clinical Trials Research Unit (OCTRU), Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, UK. Anaesthesia, Critical Care and Pain Medicine, University of Edinburgh, Edinburgh, UK; Deanery of Molecular, Genetic and Population Health Sciences and University of Edinburgh, Edinburgh, UK. Anaesthesia, Critical Care and Pain Medicine, University of Edinburgh, Edinburgh, UK. MRC Human Immunology Unit, MRC Weatherall Institute of Molecular Medicine, Oxford, UK. Department of Clinical Biochemistry, Oxford University Hospitals NHS Foundation Trust, Oxford, UK. MRC Human Immunology Unit, MRC Weatherall Institute of Molecular Medicine, Oxford, UK; Haematology Theme, NIHR Oxford Biomedical Research Centre, Oxford, UK. Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, UK. Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, UK; Intensive Care Unit, Royal Berkshire Hospitals NHS Foundation Trust, Reading, UK. Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK. Anaesthesia, Critical Care and Pain Medicine, University of Edinburgh, Edinburgh, UK; Usher Institute for Population Health Sciences, University of Edinburgh, Edinburgh, UK. Adult Intensive Care Unit, Oxford University Hospitals NHS Foundation Trust, Oxford, UK; Nuffield Department of Anaesthetics, Oxford University Hospitals NHS Foundation Trust, Oxford, UK. Radcliffe Department of Medicine, University of Oxford, Oxford, UK; Haematology Theme, NIHR Oxford Biomedical Research Centre, Oxford, UK; Department of Haematology, Oxford University Hospitals NHS Foundation Trust, Oxford, UK.