Nigeria's president has kicked off a massive effort to immunize 80 million children against polio in 23 African nations.

President Olusegun Obsanajo led officials from across the region Saturday in giving drops of the polio vaccine to children in the mainly Muslim northern city of Kano.

Islamic leaders in Kano had opposed the polio vaccination for nearly a year, leading to a polio outbreak across West Africa. They said the vaccine was contaminated with anti-fertility agents, a charge health officials denied.

The Global Polio Eradication Initiative, which is coordinating the latest campaign, say it the largest ever cross-border polio initiative in history.

The effort will get underway in earnest next week, when health workers go door-to-door to try to immunize every child across west and central Africa and war-ravaged Sudan.