For example, five hundred thousand babies are born each month in parts of northern India. It is hard to reach and vaccinate all these children. Armed conflicts and other disputes in Pakistan and Afghanistan have interfered with -- or stopped -- anti-polio campaigns.

FAITH LAPIDUS: In two thousand three, Nigeria stopped providing vaccine against polio for almost a year. False reports about the vaccine caused the stoppage. The reports said the vaccine gave people the disease AIDS. Other reports said it prevented people from having children.

Nigeria had many cases of polio after the vaccinations ended. The disease also spread to other nations.

By August of two thousand seven, however, the polio news in the nation seemed hopeful. Nigeria had reported a major reduction in polio cases after January. Then unwelcome news came. Sixty-nine children in the northern part of the country developed paralytic polio.

BOB DOUGHTY: Some of the infected children had received the Sabin oral polio vaccine. The vaccine contains weakened poliovirus that protects well against type one poliovirus. But in Nigeria, some of the vaccine had made a harmful genetic change.

FAITH LAPIDUS: Critics have questioned the continued use of the Sabin oral polio vaccine in the international campaign against polio. They say its link to infection with the disease makes the vaccine unacceptable.

Nine years ago, American health officials stopped suggesting use of that vaccine. They said the reason was to end the possibility of paralytic polio linked to it.