The virus test strains and their respective culture media were as follows: poliovirus type 1 (Mahoney/Pette, Stephan Angeloff Institute of Microbiology), cultivated in FL cells (maintenance medium DMEM without serum), virus titre 1.3×109 plaque-forming units/mL; human rotavirus strain Wa, cultivated in Ma-104 cells without serum, virus titre 107.8 cell culture infective dose CCID50/mL;