1 Department of Medicine, Imperial College, London, UK; NIHR Health Protection Research Unit in Respiratory Infections, Imperial College, London W2 1PG.
2 Virus Reference Department, National Infection Service, Public Health England, Colindale, London, UK; NIHR Health Protection Research Unit in Respiratory Infections, Imperial College, London W2 1PG.
3 National Heart and Lung Institute, Imperial College, London W2 1PG; NIHR Health Protection Research Unit in Respiratory Infections, Imperial College, London W2 1PG.
4 Department of Medicine, Imperial College, London, UK; NIHR Health Protection Research Unit in Respiratory Infections, Imperial College, London W2 1PG. Electronic address: [email protected].