The Department of Health has recently announced the implementation of annual vaccination for all those aged 18 years and under, with live attenuated influenza vaccine (LAIV), which is delivered as a nasal spray. The programme will begin in the influenza season, from September 2013, with children aged 24 years of age, and older children being included from the influenza season of 2014. Therefore this study seeks primarily to measure antibody responses to the LAIV vaccination over three subsequent years and will involve six blood samples, six dried blood spots (taken from the end of the blood sample needle) and six oral fluid samples - before and three weeks after each vaccination each year. These samples will allow us to assess how the immune system responds to the vaccinations in terms of the antibodies that are present.