by the vaccinia virus prime vaccinia virus boost administration is substantially the same preferably at least the same as that induced by dna prime vaccinia virus boost administration as assessed by the number of ifn u03b3 producing cells 10 6 spleen cells see also experimental section the strength of a ctl response as measured in one of the assays shown above corresponds to the level of protection thus the viruses of the present invention are particularly suitable for vaccination purposes in summary a representative vaccinia virus of the present invention is characterized by having at least one of the following properties i capability of reproductive replication in chicken embryo fibroblasts cef but no capability of reproductive replication in a human cell line known to permit replication with known vaccinia strains ii failure to replicate in vivo in those animals including humans in which the virus is used as a vaccine or active ingredient of a pharmaceutical composition iii induction of a higher specific immune response compared to a known vaccinia strain and or iv induction of at least substantially the same level of a specific immune response in vaccinia virus prime vaccinia virus boost regimes when compared to dna prime vaccinia virus boost regimes preferably the vaccinia virus of the present invention has at least two of the above properties and more preferably at least three of the above properties most preferred are vaccinia viruses having all of the above properties representative vaccinia virus strains are mva 575 deposited on dec 7 2000 at the european collection of animal cell cultures ecacc with the deposition number v00120707 and mva bn deposited on aug 30 2000 at ecacc with.