1 Infection, Immunity, Inflammation and Physiological Medicine, UCL Great Ormond Street Institute of Child Health, London, WC1N 1EH, UK; Save the Children, Freetown, Sierra Leone; Save the Children, London, UK. Electronic address: felicity.fitzgerald@ucl.ac.uk.
2 Ola During Children's Hospital, Sierra Leone Ministry of Health, Freetown, Sierra Leone.
3 Save the Children, Freetown, Sierra Leone; Save the Children, London, UK; Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, London, UK.
4 Department of Clinical Research, London School of Hygiene and Tropical Medicine, London, UK.
5 34 Military Hospital, Republic of Sierra Leone Armed Forces, Freetown, Sierra Leone.