Use of a multiple restriction fragment length polymorphism method for detecting vaccine-derived polioviruses in clinical samples.

Since the announcement of the WHO program for the global eradication of poliomyelitis and the establishment of epidemiological and virological surveillance, the emergence and circulation of pathogenic vaccine-derived polioviruses (VDPV) presenting >1% nucleotide divergence from the sequence of the original vaccine strain have been demonstrated in certain regions. We developed and used a multiple restriction fragment length polymorphism (RFLP) method to investigate the frequency of these VDPV in a population with a high level of oral poliovirus vaccine coverage in northwestern Russia. Modified RFLP profiles were found to be strongly correlated with the presence of mutations and recombination events in vaccine strains. We found that a substantial proportion of vaccine strains had high percentages of nucleotide substitutions (>0.5%), including a type 3 VDPV with 1.4% nucleotide divergence. These findings indicate that VDPV or pre-VDPV strains are not rare in certain populations with high levels of vaccine coverage. The multiple RFLP method appears to be a simple and rapid tool for monitoring such strains, which could jeopardize the benefits of the eradication program.