Most of the world is free of indigenous transmission of wild, or naturally-occurring, poliovirus. Only six cases of polio caused by the wild virus have been reported so far in 2017. Polio remains endemic in three countries: Afghanistan, Nigeria and Pakistan. Until poliovirus transmission is interrupted in these countries, all countries remain at risk of importation of polio, especially vulnerable countries with weak public health and immunization services and travel or trade links to endemic countries.
This is different from vaccine-derived polio, which happens if a population is seriously under-immunized and an excreted vaccine-virus spreads in the immediate community. This is a very rare occurrence, as it happened in Israel and Palestine during 2013-2014, and in Syria and the Democratic Republic of the Congo during 2017.
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