Testing has confirmed a third case of wild polio virus infection in Mungono, Borno state, days after two previous infections were detected.
The latest infection crippled a toddler from an enclave community only recently liberated from Book Haram.
Insurgency and attack on health workers have thwarted immunisation of children for years, cutting off communities and any access to health care.
The World Health Organisation has raised concerns more cases could emerge in coming weeks and months as humanitarian assistance reaches previously cut-off enclaves.
The new cases emerged after Nigeria had gone a stretch of two years without any infection and would have been declared polio-free by July 2017.