Seasonal influenza infection results in a T cell response to the virus which can protect against subsequent infection. However over the course of a few years these responses decline below protective levels. The new vaccine being tested in this study is designed to boost these T cell responses back to protective levels. Even responses that may be too low to be reliably quantified by currently available assays may still be boosted to high levels by a single dose of recombinant MVA. Since the internal proteins vary little between influenza subtypes, this could result in a 'universal' vaccine against influenza A. If the need to continually reformulate the vaccine in response to mutations in the viral coat proteins can be removed, the universal vaccine could be produced in large amounts and used more widely than the existing seasonal 'flu vaccines, thus protecting the population against currently circulating viruses and new virus types that are at present only found in avian species.