LONDON (AP) — In a story Jan. 22 about polio in Mozambique, The Associated Press reported erroneously the number of polio cases. There is one case, not two.

A corrected version of the story is below:

Global health officials say they have identified one case of polio in Mozambique caused by a mutated virus in the vaccine, marking another setback for attempts to eradicate the crippling disease.

In a report this week, the World Health Organization and partners said they confirmed polio in a 6-year-old girl. Officials said isolates tested found she was infected by a virus derived from the vaccine. Another person was also infected, but not paralyzed. In rare cases, the virus in the oral polio vaccine can mutate into a form capable of causing new outbreaks.

Officials have missed repeated deadlines to wipe out polio and are facing numerous challenges in the remaining countries where the disease circulates. Last year there were dozens of cases elsewhere in Africa including Nigeria, Congo and Somalia.