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pubmed:abstractText |
Sporadic cases of paralytic poliomyelitis are being reported with increasing frequency, particularly in unvaccinated persons, in several countries in which the disease had been absent for several years following adequate initial vaccination programmes. In Ontario, two paralytic cases occurred in unvaccinated children after several disease-free years. Detailed studies of the strains of poliovirus type 1 isolated from these patients showed that they were not vaccine strains. Contact surveillance in one case showed that 21 originally unvaccinated contacts were also excreting virulent virus.
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