Genomic features of intertypic recombinant Sabin poliovirus strains excreted by primary vaccinees

The trivalent oral poliomyelitis vaccine (OPV) contains three different pol iovirus serotypes. It use therefore creates particularly favorable conditio ns for mixed infection of gut cells, and indeed intertypic vaccine-derived recombinants (VdRec) have been frequently found in patients with vaccine-as sociated paralytic poliomyelitis, Nevertheless, there have not been extensi ve searches for VdRec in healthy vaccinees following immunization with OPV, To determine the incidence of VdRec and their excretion kinetics in primar y vaccinees, and to establish the general genomic features of the correspon ding recombinant genomes, we characterized poliovirus isolates excreted by vaccinees following primary immunization with OPV, Isolates were collected from 67 children 2 to 60 days following vaccination. Recombinant strains we re identified by multiple restriction fragment length polymorphism assays. The localization of junction sites in recombinant genomes was also determin ed, VdRec excreted by vaccinees were first detected 2 to 4 days after vacci nation. The highest rate of recombinants was on day 14, The frequency of Vd Rec depends strongly on the serotype of the analyzed isolates (2, 53, and 7 9% of recombinant strains in the last-excreted type 1, 2, and 3 isolates, r espectively). Particular associations of genomic segments were preferred in the recombinant genomes, and recombination junctions were found in the gen omic region encoding the nonstructural proteins. Recombination junctions ge nerally clustered in particular subgenomic regions that were dependent on t he serotype of the isolate and/or on the associations of genomic segments i n recombinants, Thus, VdRec are frequently excreted by vaccinees, and the p oliovirus replication machinery requirements or selection factors appear to act in vivo to shape the features of the recombinant genomes.