Royal Belfast Hospital for Sick Children - Emergency Department, Queen’s University - Wellcome Wolfson Institute for Experimental Medicine, Royal Belfast Hospital for Sick Children, Royal Belfast Hospital for Sick Children, Royal Belfast Hospital for Sick Children, Public Health England - Immunisation and Countermeasures Division, Queen’s University - Wellcome Wolfson Institute for Experimental Medicine, Public Health England - Immunisation and Countermeasures Division, Royal Belfast Hospital for Sick Children - Emergency Department, Public Health England - Immunisation and Countermeasures Division, Cardiff and Vale University Health Board, Royal Belfast Hospital for Sick Children, Public Health England - Immunisation and Countermeasures Division, Royal Hospital for Children, Public Health England - Virus Reference Department, Public Health England, Queen's University Belfast - Mathematical Sciences Research Centre, Public Health England - Immunisation and Countermeasures Division, Queen's University Belfast - Mathematical Sciences Research Centre, Royal Belfast Hospital for Sick Children, Public Health England - Immunisation, Hepatitis, and Blood Safety Department, Public Health England - Immunisation and Countermeasures Division and Public Health England - Immunisation and Countermeasures Division