A highly evolved double recombinant (type 1-type 2-type 1) Sabin vaccine-derived poliovirus was isolated from a 7-month-old baby, suggesting the vaccine strain circulated and evolved for approximately 2 years before causing paralytic disease.
Case Report (n=2)
The study demonstrates the potential for long-term circulation and increased neurovirulence of Sabin vaccine strain derivatives, highlighting challenges for the global poliomyelitis eradication program.
Successful implementation of the global poliomyelitis eradication program raises the problem of vaccination against poliomyelitis in the posteradication era. One of the options under consideration envisions completely stopping worldwide the use of the Sabin vaccine. This strategy is based on the assumption that the natural circulation of attenuated strains and their derivatives is strictly limited. Here, we report the characterization of a highly evolved derivative of the Sabin vaccine strain isolated in a case of paralytic poliomyelitis from a 7-month-old immunocompetent baby in an apparently adequately immunized population. Analysis of the genome of this isolate showed that it is a double (type 1-type 2-type 1) vaccine-derived recombinant. The number of mutations accumulated in both the type 1-derived and type 2-derived portions of the recombinant genome suggests that both had diverged from their vaccine predecessors approximately 2 years before the onset of the illness. This fact, along with other recent observations, points to the possibility of long-term circulation of Sabin vaccine strain derivatives associated with an increase in their neurovirulence. Comparison of genomic sequences of this and other evolved vaccine-derived isolates reveals some general features of natural poliovirus evolution. They include a very high preponderance and nonrandom distribution of synonymous substitutions, conservation of secondary structures of important cis-acting elements of the genome, and an apparently adaptive character of most of the amino acid mutations, with only a few of them occurring in the antigenic determinants. Another interesting feature is a frequent occurrence of tripartite intertypic recombinants with either type 1 or type 3 homotypic genomic ends.
Cherkasova et al. (2002) conducted a case report in Vaccine-associated paralytic poliomyelitis (n=2). Sabin oral poliovirus vaccine (OPV) derivative vs. Sabin reference strains was evaluated on Genomic characterization and mutation accumulation. A highly evolved double recombinant (type 1-type 2-type 1) Sabin vaccine-derived poliovirus was isolated from a 7-month-old baby, suggesting the vaccine strain circulated and evolved for approximately 2 years before causing paralytic disease.