WHO said the PNG outbreak is linked to strains circulating in Indonesia, posing a serious risk to other countries in the region.

Further testing by WHO, the PNG Department of Health, UNICEF and local provincial health authorities confirmed the virus in the two healthy children in Lae, and genetic sequencing showed the strain was linked to polio circulating in Indonesia.

WHO says wild poliovirus type 2 was eradicated in 1999 and type 3 was wiped out in 2020. As of 2022, there were just two countries still impacted by wild poliovirus type 1 — Pakistan and Afghanistan.

For almost 40 years, the world has been fighting to keep levels of polio as close to zero as possible. 

In PNG, WHO says polio was wiped out in 2000 but the country has been susceptible to cases due to low immunisation rates and "suboptimal" surveillance.

The country experienced a small polio outbreak in 2018 but it was brought under control the same year and there have been no detected cases until now.

Notes distributed by WHO's representative in PNG, Dr Sevil Huseynova, suggest that the latest polio outbreak in the country can be attributed low vaccine rates and the virus's transmissibility.

"As these challenges significantly increase, the risk of vaccine-preventable disease outbreaks and hinder our ability to detect and respond to cases promptly.

"Polio is a highly infectious disease, and in communities with low polio immunisation rates, the virus quickly spreads from one person to another."

Linda Selvey, an honorary associate professor at the University of Queensland's School of Public Health, told ABC radio's PM program that the risk of polio spreading to Australia "would be fairly low".

Australia has not had a major outbreak of polio since 1961, and Australian children are now vaccinated against the virus as part of their routine immunisation as infants.

Dr Selvey has worked on polio eradication programs in the past in India and Nepal and said that for PNG, the impact of the virus's spread could be dire.

"I'm concerned about the outbreak from the perspective of the people in Papua New Guinea in particular because they generally have very low immunisation coverage," she said.

"While they haven't actually had a clinical case of polio, it would be quite possible.

"The other thing is because health services are not great in many parts of PNG, a child might get polio without it being detected, so then that means there's a chance of surface spread."

Despite that risk and WHO saying on Thursday that "polio anywhere is a threat everywhere", Dr Selvey says Australia's immunisation rates provide the country with a high level of protection.

"We're only at risk if we have a population who's not immune. Generally, I think our immunisation coverage in Australia is still pretty good, even though it has fallen in the last few years," she said.

"We also have very good sanitation and so-on, we don't generally live in particularly crowded areas. I would think that the risk would be fairly low. 

"The greatest risk would be in the parts of Queensland, in particular in the Torres Strait, where there's closer movement of people between Papua New Guinea and Australia and also where the housing and so on is less optimal."