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Aims: The route of transmission of wild and circulating vaccine-derived polioviruses remains controversial, between respiratory and faecal-oral, and we aim to identify the most plausible one to settle the controversy. Methods: We explored available epidemiological clues and evidence in support of either route in order to arrive at an evidence-based conclusion. Results: Historically the original concept was respiratory transmission based on epidemiological features of age distribution, which was later revised to faecal-oral as the rationale for popularising the live attenuated oral polio vaccine in preference to the inactivated poliovirus vaccine. Through epidemiological logic, we find no evidence for the faecal-oral route from available studies and observations, but all available information supports the respiratory route. Conclusions: The route is respiratory, not faecal-oral. The global polio eradication initiative assumed it was faecal-oral – and its gargantuan efforts based on this assumption have failed in two ways: eradication remains pending and circulating vaccine-derived polioviruses have seeded widely. With clarity on the route of transmission the choice of vaccine is also clear – it can only be the inactivated poliovirus vaccine. [ABSTRACT FROM AUTHOR]

To explore if intestinal immunity induced by infection with live viruses in the oral poliovirus vaccine (OPV) is essential, necessary or even helpful in interrupting transmission of wild poliovirus (WPV) for global polio eradication. We reviewed the biology of virus-host interactions in WPV infection and its alterations by OPV-induced immunity for direct evidence of the usefulness of intestinal immunity. We also explored indirect evidence by way of the effect of the inactivated poliovirus vaccine (IPV) on the biology and on transmission dynamics of WPV. Immunity, systemic and intestinal, induced by infection with WPV or vaccine viruses, does not prevent re-infection with WPV or vaccine viruses respectively, when exposed. Such re-infected hosts shed virus in the throat and in faeces and are sources of further transmission. Immunity protects against polio paralysis-hence reinfection always remain asymptommatic and silent. Vaccine virus-induced intestinal immunity is not necessary for polio eradication. The continued and intensive vaccination efforts using OPV under the assumption of its superiority over IPV have resulted in the well-known undesirable effects, namely vaccine associated paralytic polio and the emergence of de-attenuated circulating vaccine-derived polioviruses, in addition to the delay in completing global WPV eradication. [ABSTRACT FROM AUTHOR]