It follows Nigeria going more than a year without a case of wild – naturally occurring – polio.
This announcement by WHO was made at a meeting of the Global Polio Eradication Initiative (GPEI) in New York.
This means Nigeria, which in 2012 accounted for more than half of all polio cases worldwide, has recorded a major breakthrough in its fight against polio.
The country last reported a case of wild poliovirus in July 24, 2014, and a full 12 months have passed without a fresh case of the paralysing disease.
Only two countries – Pakistan and Afghanistan are still on the polio-endemic list and WHO has assured it will support their efforts to join list of nations that had been declared free of the disease.
Jean Gough, Unicef country representative in Nigeria, reported that “This is an important milestone, but it is too early to celebrate. We need to continue the efforts at every level if polio is to be eradicated.”
Polio is spread by poor sanitation and contaminated water and usually affects children.
The virus attacks the nervous system and can cause irreversible paralysis – usually of the legs – within hours.
Nigeria progress against polio has been hard-fought.
In 2003, some northern states boycotted the oral polio vaccine for nearly a year after scare stories that it caused sterilization.
It led to the virus spreading to many countries that had been declared polio free.
In 2013 nine vaccinators were shot dead in Kano. But instead of being a deterrent, it galvanised support at every level.
The Nigeria government declared polio a national health emergency and greatly increased the number of vaccinators.
And community and religious leaders voiced their support.
As a result, the number of families refusing to have their children immunized has decreased sharply.
The success has come despite the Islamist militant insurgency in north-east Nigeria.
Earlier this month Unicef said half a million children had fled attacks by Boko Haram over the past five months.
Vaccine teams have been focussing attention on displaced families who have moved elsewhere in Nigeria, as well as fleeing to neighbouring countries like Cameroon, Chad and Niger.