The study will be an open label, randomised, parallel group, multicentre clinical trial conducted by a consortium of the leading paediatric vaccine research units in the United Kingdom. The study will recruit healthy children 6 months to 12 years of age. Children with previously laboratory confirmed infection with swine flu will be excluded, as will those that have received a treatment course of oseltamivir. Children with immune deficiencies and egg allergy will also be excluded.