Natural genetic exchanges between vaccine and wild poliovirus strains in humans

In a previous study of poliovirus vaccine-derived strains isolated from pat ients with vaccine-associated paralytic poliomyelitis (VAPP) (9, 11), we re ported that a high proportion (over 50%) of viruses had a recombinant genom e. Most mere intertypic vaccine/vaccine recombinants. However, some had res triction fragment length polymorphism (RFLP) profiles different from those of poliovirus vaccine strains. We demonstrate here that five such recombina nts, of 88 VAPP strains examined, carried sequences of wild (nonvaccine) or igin. To identify the parental wild donor of these sequences, we used RFLP profiles and nucleotide sequencing to look for similarity in the 3D polymer ase-coding region of 61 wild, cocirculating poliovirus isolates (43 type 1, 16 type 2, and 2 type 3 isolates). In only one case was the donor identifi ed, and it was a wild type 1 poliovirus. For the other four vaccine/wild re combinants, the wild parent could not be identified. The possibility that t he wild sequences were of a non-poliovirus-enterovirus origin could not be excluded. Another vaccine/wild recombinant, isolated in Belarus from a VI-I PP case, indicated that the poliovirus vaccine/wild recombination is not an isolated phenomenon. We also found wild polioviruses (2 of 15) carrying va ccine-derived sequences in the 3' moiety of their genome. All these results suggest that genetic exchanges with wild poliovirus and perhaps with nonpo liovirus enteroviruses, are also a natural means of evolution for polioviru s vaccine strains.