apparently it was likely caused by shedding from the OPV the Oral Polio vaccine which uses live virus....
“The recently reported case was identified in a child who was 3 years and 9 months old and showed symptoms of paralysis, said Oliver Rosenbauer, a spokesman for the WHO. He said this was an isolated case of a vaccine-derived poliovirus, a mutated form of the virus that can be fostered by the oral vaccine used in many countries and can cause paralysis when spread over a period of time between unvaccinated children.
“It is definitely not a wild poliovirus, imported from Pakistan or Afghanistan,” Mr. Rosenbauer said in an email, referring to the main and most dangerous form of the virus. “That we know for certain. But more needs to be found out, in terms of where or how this strain emerged, and whether it is circulating.”