The effect of sequences in the 5' non-coding region on the replication of polioviruses in the human gut.

The genomic sequences of a portion of the 5' non-coding region of polioviruses excreted by recipients of the Sabin vaccine strains of poliovirus were examined. It was found that in all three types a residue changed in the course of excretion to give a sequence representing the consensus of poliovirus sequences. For type 1 this residue was at position 481, which altered in half the vaccines, for type 2 it was at position 480, which altered in all vaccinees and for type 3 it was at position 472 in all vaccinees, as previously reported. Other vaccine strains unrelated to the Sabin strains but used in limited vaccination programmes did not have such changing residues. It was concluded that these regions indicated sequences that were strongly selected during replication in the human gut. Such sequences were further defined by examination of strains of poliovirus unrelated to the vaccine strains, the sequences of which may be expected to vary at less stringently defined regions.