The United Nations said it was confident of stopping the spread of polio in Nigeria by the end of the year as it races to stem an epidemic fueled by a 10-month ban on vaccinations in a northern state.

The predominantly Muslim state of Kano lifted the boycott last month and restarted polio immunizations, but not before the crippling virus had spread across Nigeria and had also infected 10 African states previously declared polio-free.

Kano’s state government banned the vaccines last September over fears they had been adulterated with HIV and infertility agents by Western powers trying to depopulate the Islamic world.

Gerrit Beger, spokesman for the United Nations children’s agency UNICEF, said 58 percent of 4.1 million children in Kano had been vaccinated after a July immunization drive. Three more campaigns were planned over the next three months.

Beger said Kano needed to immunize at least 90 percent of children in the state to stop polio spreading and was confident that figure could be reached by October.

Nigeria now accounts for three-quarters of the new polio infections worldwide, largely because of Kano’s ban, and this year’s immunization campaign is key to a global effort to eradicate polio worldwide by next year.

Health workers said some of the children not immunized in July’s campaign had been kept away by parents with lingering safety fears, even after the state declared the vaccine safe.

“There were rejections here and there. We hope the second phase which takes off in the first week of September will be better,” said Aminu Mohammed, a member of UNICEF’s social mobilization committee.

Beger said UNICEF was cooperating with non-government organizations in Kano such as women’s groups to overcome people’s fears about the vaccine.

Polio, which afflicts children mainly under five years, is caused by a virus that invades the nervous system and can cause total paralysis or death.

The vaccine works by infecting patients with a benign form of polio and giving them immunity to the virulent strain.