Clinical studies The safety and immunogenicity of this BCG prime-MVA85A boost vaccination strategy has now been evaluated in a series of small-scale Phase I studies in the UK. MVA85A was the first candidate TB vaccine in clinical trials anywhere in the world in September 2002, and is currently the only one in clinical trials in Africa . The main immunological read-out used in these clinical trials is the ex-vivo IFN-γ Elispot assay, which is used to assess specific T cell responses to tuberculin PPD, antigen 85 complex and pools of overlapping peptides spanning the length of antigen 85A. The best immunological correlate of protection in murine and human TB is the secretion of IFN-γ from sensitised T cells.