A Phase III/IV Open-label Study of the Immunogenicity and Safety of a Single Dose of a Live Attenuated Influenza Vaccine (LAIV) (FluenzTM) for Each of Three Successive Years in Children naïve to, or in Previous Receipt of the AS03B Adjuvanted H1N1 (2009) Influenza Vaccine (Pandemrix ™).

Inclusion Criteria: * Parent/legal guardian gives written informed consent for participation of their child in the study. * Male or female aged 4 years (+364 days) to 8 years (+364 days) on the day of consent. * Documented prior receipt of Pandemrix, or no evidence in the medical notes of never having had pandemic influenza vaccine. Exclusion Criteria: * Absolute exclusion criteria. The participant may not enter the study if ANY of the following apply: From Fluenz Summary of Product Characteristics (SPC): * Hypersensitivity to the active substances, to any of the excipients (e.g. gelatin; see appendix 1), to gentamicin (a possible trace residue), to eggs or to egg proteins (e.g. ovalbumin). * Children and adolescents who are clinically immunodeficient due to conditions or immunosuppressive therapy such as: acute and chronic leukaemias; lymphoma; symptomatic HIV infection; cellular immune deficiencies; and highdose corticosteroids. FLUENZ is not contraindicated for use in individuals with asymptomatic HIV infection; or individuals who are receiving topical/inhaled corticosteroids or lowdose systemic corticosteroids or those receiving corticosteroids as replacement therapy, e.g. for adrenal insufficiency. * Children and adolescents younger than 18 years of age receiving salicylate therapy because of the association of Reye's syndrome with salicylates and wildtype influenza infection. Study specific exclusions: * Any contraindication to vaccination as specified in the "Green Book"Immunisation against Infectious Disease, HMSO. * known bleeding diathesis (or any condition that may be associated with a prolonged bleeding time). * Any other significant condition or circumstance which, in the opinion of the investigator, may either put the participant at risk because of participation in the study, or may influence the result of the study, or the participant's ability to participate in the study. \*Temporary Exclusion Criteria From the SPC: • The concurrent use of FLUENZ with antiviral agents that are active against influenza A and/or B viruses has not been evaluated. However, based upon the potential for influenza antiviral agents to reduce the effectiveness of FLUENZ, it is recommended not to administer the vaccine until 48 hours after the cessation of influenza antiviral therapy. Administration of influenza antiviral agents within two weeks of vaccination may affect the response of the vaccine. Because of this information in the SPC, should any child be given these medications the administration of LAIV would be delayed as specified. Study specific: * Fever (sublingual temperature ≥ 38°C) * Received any blood or blood products within the past 12 weeks.