The respiratory route of transmission of virulent polioviruses.

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.