An outbreak of polio has been confirmed in Papua New Guinea, 18 years after the country was declared free of the disease.
The World Health Organization (WHO) says the virus was detected in a six-year-old boy in April.
The same strain of the virus has now been detected in other healthy children in the same community, making it officially an outbreak.
Polio has no cure and can lead to irreversible paralysis.
It mainly affects children under the age of five, and can only be prevented by giving a child multiple vaccine doses.
"We are deeply concerned about this polio case in Papua New Guinea, and the fact that the virus is circulating," said Pascoe Kase, Papua New Guinea's heath secretary.
"Our immediate priority is to respond and prevent more children from being infected."
The US Centers for Disease Control and Prevention said at the end of last week that the same virus that was found in the six-year-old boy was also found in samples taken from two healthy children in the same community, the WHO said.
This means the virus is circulating in the community, representing an outbreak, it added.
Immediate steps to stop the spread of the highly contagious disease include large-scale immunisation campaigns and strengthening surveillance systems that help detect it early, reports BBC.
Papua New Guinea has not had a case of wild poliovirus since 1996, and the country was certified as polio-free in 2000 along with the rest of the WHO Western Pacific Region.
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