Post-Authorization Safety Study of GSK Biologicals' Pandemic Influenza Vaccine (H1N1) in the United Kingdom

Inclusion Criteria: * Written informed consent, and assent where appropriate, obtained from the subject/from the subject's parent(s)/ Legally Acceptable Representative(s) (LAR). * A male or female subject vaccinated with a first dose of GSK Biologicals' H1N1 pandemic influenza vaccine * shortly (\<24h) before being recruited in the study, and * within a GP practice participating in the study and where the subject is registered. * Subjects who the Investigator believes that they and/or their parent(s)/LAR can and will comply with the requirements of the protocol Exclusion Criteria: * Subjects already vaccinated with any other H1N1 pandemic vaccine before study enrolment. * Child in care