The national Health minister on Friday declared South Sudan polio free after an outbreak was reported in Eastern Equatoria and Northern Bahr El Ghazal States in August.
Riek Gai Kok said there was an error in the referral laboratory in Kenya during the transportation of the samples for testing, Bakhita Radio reported.
He said the polio positive samples were confirmed in Atlanta, USA, to be from Somalia and not from South Sudan.
Dr Gai said the immunization campaign launched in the country on Thursday will go ahead as planned because there were polio out-breaks reported in Somalia and Nigeria.
He commended WHO and other health partners for supporting the country in rendering services to citizens.
Vice President James Wani Igga on Thursday launched the polio immunization campaign in Juba following alleged reports of polio outbreak in Eastern Equatoria and Northern Bahr El Ghazal States.