The next study, which completed enrolment in the UK in February 2006, assessed the safety and immunogenicity of MVA85A in healthy volunteers who were latently infected with M.tb. Twelve latently infected healthy subjects were vaccinated with a single dose of 5 x 10^7pfu MVA85A. In this study, latent M.tb infection was determined by tuberculin skin testing and ex-vivo IFN-γ Elispot responses to two M.tb specific antigens, ESAT6 and CFP10. Follow-up involved detailed radiological and clinical assessment of the safety of this vaccine in M.tb infected subjects. We found that MVA85A is equally safe and equally immunogenic in this latently infected population as it is in the population vaccinated with BCG (Sander et al, unpublished data). We have also conducted a dose finding study looking at two further doses of MVA85A, 1 x 10^7pfu and 1 x 10^8 pfu. Twelve subjects were vaccinated with each dose. The preliminary results show the vaccine is significantly more immunogenic at the higher (1 x 10^8 pfu) dose but the immunogenicity of the lower (1 x 10^7 pfu) dose is comparable with the standard (5 x 10^7pfu) dose.