A two-year-old girl in Ghana has tested positive to having vaccine-derived polio.

This strain of polio occurs when an unvaccinated person catches the virus from somebody else who has been given the vaccine, often through their faeces in unsanitary housing.

The toddler was admitted to Cheperoni District hospital in north-east Ghana in July after she suddenly got weak legs. She later developed paralysis, said the head of Ghana's national health service Dr Anthony Nsiah Asare in a statement.

Polio

Image caption: Ghanaian authorities said they will increase vaccinations in the affected area

He called the confirmation of the case a national health emergency.

"The global community is in the polio end game and a case of polio constitutes a public health emergency of national concern," he said.

He added that vaccinations in the affected area will be increased.

Outbreaks of this kind can be stopped with two to three rounds of immunisations, according to the Global Polio Eradication Initiative

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BBC health correspondent James Gallagher reports that cases of vaccine-derived polio are an expected part of a vaccination programme, but can be prevented by immunising all children.

He said there had also been vaccine-derived polio cases in nine countries - including Angola, Central African Republic and Somalia - this year, but the incidences did not affect when a country was declared wild polio-free.

Africa is on track to become free of wild polio.

The last recorded case of wild polio was more than three years ago in Nigeria and the country is expected to be officially declared polio-free by the World Health Organization early next year.