The programme will see all children under the age of five in 13 countries immunised from Saturday “in a coordinated effort to raise childhood immunity to polio,” it added.
The countries are Benin, Cameroon, Central African Republic, Chad, Ivory Coast, Democratic Republic of Congo, Guinea, Liberia, Mali, Mauritania, Niger, Nigeria and Sierra Leone.
Once a worldwide scourge, polio is still endemic in three countries—Nigeria, Afghanistan and Pakistan.
This year, the WHO has recorded four cases of polio—two each in Pakistan and Afghanistan.
Last year, there were 37 cases globally.
The four-day campaign in Africa by 190,000 vaccinators is part of the response to the discovery of three cases of polio in the insurgency-wracked state of Borno in northeast Nigeria last year.
Before then, the west African country had not reported a case of polio in two years and was on track to be certified free of the virus this year.
Rod Curtis, from the UN children’s fund UNICEF in Borno, told AFP another campaign would take place at the end of April in the countries around Lake Chad.
Lake Chad forms the border between Nigeria, Niger, Chad and Cameroon, which have all been affected by Boko Haram’s Islamist insurgency.
“It’s funded by international donors, local governments and the government of Japan who spent $33 million specifically to support this campaign,” he said.