Political leaders and health workers launched a drive Saturday to immunise more than 80 million children against polio in 23 African nations and fight back against a resurgence of the crippling disease.

Campaigners had been hoping to eradicate polio this year or next but the virus has spread in the past 18 months to 12 countries where it had been wiped out, in part because the northern Nigerian state of Kano banned the vaccination.

Authorities imposed the ban last year because local Muslim leaders alleged the vaccines had been tainted to reduce fertility and spread HIV in a Western plot against Islam. They reversed course in July this year after 10 months of pressure.

“Building a strong nation today in order to guarantee a virile future…is our collective responsibility,” Nigerian President Olusegun Obasanjo told thousands of people packed into a stadium in Kano.

“Let us pride ourselves on a polio free Africa and Nigeria,” he told officials from the United Nations and European Union, as well as African Union Commission President Alpha Oumar Konare and a range of Nigerian dignitaries.

More than 650 African children have been paralyzed by polio this year, accounting for more than 85 percent of the global total, according to the partnership of U.N. agencies and other groups spearheading efforts to eradicate the disease.

“The ban on immunisation in Kano was a key factor in allowing the virus to spread back into polio-free parts of Africa,” said Kent Page, a spokesman for U.N. children’s fund UNICEF in West and Central Africa.

“It provided the spark and the region ignited,” he said, adding that inadequate campaigns in other parts of Nigeria and surrounding countries had made matters worse.

Polio, which mainly afflicts children under five, is caused by a virus that invades the nervous system and can cause total paralysis or death. It is one of very few diseases than can be fully eradicated if enough children are vaccinated.

Health experts say political leaders need to back vaccination - usually administered by mouth in at least three doses - to underscore its importance to citizens.

“Despite the great gains made by the Global Polio Eradication Initiative around the world, polio is now fighting back in Africa,” said E.M. Samba, director of the World Health Organization’s regional office for Africa.

“Now, more than ever, we have to stop polio forever, and we cannot do it alone,” Samba said.

The new campaign will cover 22 countries in West and Central Africa as well as Sudan. The first wave of vaccinations will begin later this month, with a second wave in November and further rounds throughout 2005, officials say.