Highly divergent neurovirulent vaccine-derived polioviruses of all three serotypes are recurrently detected in Finnish sewage

In Finland, surveillance of potential re-emergence of poliovirus transmission is mainly based on environmental surveillance, i.e. search for infectious poliovirus in sewage samples. Since December 2008, 21 genetically highly divergent, neurovirulent vaccine-derived polioviruses (VDPV) have been isolated from sewage in Tampere, Finland. While the source of the VDPV is unknown, characteristics of the viruses resemble those of strains isolated from immunodeficient, persistently infected persons. No cases of suspected poliomyelitis have been reported in Finland since 1985.