Nigeria was on track of being certified free of the virus before two other polio cases were discovered in the same area in Borno State in August.
“A third child has been paralyzed by wild poliovirus type one (WPV1) in Borno state,” WHO said in a statement.
The latest case, Mucznik said, concerned a two-year-old boy suffering from the onset of paralysis on August 6 in the Monguno area.
“Genetic sequencing of the isolated viruses suggests they are most closely linked to WPV1 last detected in Borno in 2011, indicating the strain has been circulating without detection since that time,” Mucznik said.
Though there is no cure, it can be prevented through immunisation.
Nigeria has already responded to the new discovery a wide scale immunisation campaign.
The campaign is expected to continue until November and includes the neighbouring areas of Chad, Cameroon and Niger.
Professor Isaac Adewole, Nigeria’s Health Minister warned in August that the affected areas “have had their health facilities destroyed by insurgents” and “accessibility was a barrier to service provision.”