The present invention relates to viral strains derived from the vaccinia virus Lister VACV-107 and to pharmaceutical composition containing the viral strains. More particularly, the present invention relates to a viral strain derived from the vaccinia virus Lister VACV-107 wherein strain contains in its genomic sequence (SEQ ID N°1) at least one deletion selected from the group consisting of: deletion of the nucleotides 19758 to 28309 in the sequence ID NO°1 (Δ18), deletion of the nucleotides 161293 to 164811 in the sequence ID NO°1 (Δ20), deletion of the nucleotides 181231 to 183304 in the sequence ID NO°1 (Δ21), deletion of the nucleotides 6118 to 9677 in the sequence ID NO°1 (Δ22), deletion of the nucleotides 1833 to 3574 and 185848 to 187589 in the sequence ID NO°1 (Δ23).
