PURPOSE: A cyclic double-stranded DNA, obtained by intertype recombination of Sabin 1 type strain with Sabin 2 type or 3 type strain and capable of giving a safe vaccine strain exhibiting constant properties at all times.

CONSTITUTION: A cyclic DNA capable of exhibiting infectivity for animal cells in cyclic double-stranded DNA prepared by converting poliovirus RNA gene into a double-stranded cDNA and replacing a region coding coat protein of Sabin 1 type strain cDNA with a double-stranded DNA of the corresponding genetic part (BAlI-BanI region; base Nos. 637W3550) of Sabin 2 type strain or corresponding genetic part (BalI-NdeI region; base Nos. 637W3405) of Sabin 3 type strain and producing the poliovirus. The above-mentioned DNA is transfected into animal cells, e.g. renal cells of African green monkey, and cultivated at 33.0W34.0°C to recover the resultant intertypic recombinant virus, which is further subcultured for several passages to afford a virus liquid usable as a poliovirus live vaccine.