LAGOS, Nigeria (AP) — The U.N. World Health Organization is formally removing Nigeria from the list of polio-endemic countries, meaning the entire African continent is free of the crippling disease.

A WHO statement said Monday's move comes after Nigeria reported no new cases for 15 months — after overcoming obstacles ranging from Islamic extremists who assassinated vaccinators to rumors the vaccine was a plot to sterilize Muslims.

Just 20 years ago Nigeria was recording 1,000 polio cases a year — the highest in the world.

Rotary International last week announced a donation of $26.8 million to African countries to ensure the disease doesn't return, including $6.9 million to Nigeria. Nigeria's President Muhammadu Buhari promised to increase surveillance and immunization.