In the UK, 14 mycobacterially and BCG naïve, healthy volunteers have been vaccinated with 5 x 10^7pfu MVA85A, administered intradermally. We find that MVA85A is safe and well tolerated. A single vaccination with MVA85A induces remarkably high levels of specific effector T cell responses (median IFN- γ Elispot response to Antigen 85A summed peptide pools 1153 spots per million PBMC). In addition, the safety of MVA85A in volunteers previously vaccinated with BCG has now been demonstrated in 17 volunteers. These 17 volunteers show even higher peak levels of antigen specific T cells (median response 2455 spots per million PBMC) 1 week post-vaccination than those immunized with MVA85A alone. Perhaps more importantly for the induction of T cell memory, volunteers who have been previously BCG vaccinated maintain higher levels of antigen specific T cells after MVA85A for up to 24 weeks after vaccination, when compared to those volunteers vaccinated with MVA85A alone. In contrast to this viral vector boost, the magnitude of T cell responses seen after vaccination with a leading protein/adjuvant vaccine (for malaria), RTS,S/AS02, is around 200 spots per million PBMC.