An expert says Kiwis have little to fear after a polio outbreak was been confirmed in Papua New Guinea's Morobe province for the first time in 18 years.
The World Health Organisation said a six-year-old Morobe boy went to a health centre with lower limb weakness on the April 28, and May 21, he was confirmed to have a vaccine-derived form of polio.
Last week, the United States Centres for Disease Control and Prevention said tests of stool samples from other children confirmed that the virus was circulating in the community.
The form of polio discovered in Morobe happened in an area where immunisation rates are poor, the WHO said, and the virus may have spread from the excrement of someone who was vaccinated - a very rare occurrence.
Professor Steve Chambers of Otago University said the resurgence of polio was due to a form of polio used in oral vaccines mutating.
The oral vaccine contains live, but weakened, virus cells, while the injectable form of the vaccine - which New Zealand has used for many years - does not.
"[The injection] can't mutate - that can't cause disease," Mr Chambers said.
However, Mr Chambers advised that anyone considering travelling to areas where polio incidents are regularly recorded should take care.
"If you're travelling to an area like this you should think about getting your vaccines updated," he said.
The WHO said response teams have swung into action in Morobe, investigating the outbreak and trying to isolate it, as well as immunising children in a region where few have been.
Polio mainly affects young children and had been eradicated in most of the world, with only 22 reported cases last year.