Photo: The World Health Organisation
In Papua New Guinea, more than 31 instances of polio have been detected since the disease re-emerged earlier this year.
The World Health Organisation (WHO) confirmed the numbers on Monday, as PNG launched a national immunisation campaign in Port Moresby.
The WHO declared an outbreak in May after two children were confirmed to have the virus.
Polio or poliomyelitis is a highly infectious disease that mainly affects children under five. It can also affect older age groups.
Most people who have it have no symptoms, but it can lead to irreversible paralysis in about one in 200 infections, or one percent of cases.
The virus is spread by person-to-person contact or the ingestion of contaminated virus from faeces. Because the virus multiplies in the gut of infected people, who then shed it in their stool for several weeks, it can spread through a community, particularly in areas with poor sanitation.
The WHO said over 31 detections of the virus had been confirmed in Papua New Guinea through environmental and community surveillance since May. While no cases of paralysis had been reported, the risk of further transmission remained high due to low immunisation rates and poor access to children who lived in remote areas.
The WHO also added that healthy children infected with the virus were not considered "polio cases" under its clinicial definition beause they did not have symptoms and exhibit paralysis. The two children confirmed to have the virus in May fell into this category, a spokesman said.
The WHO said the vaccine campaign would focus on the mainland provinces, of which 17 had been identified as high-risk areas. Here, both the oral polio vaccine and the polio vaccine jab were due to be administered.
The New Guinea Islands provinces had been deemed lower-risk, and one round of the polio vaccine injection had been planned.
"This moment represents more than just a public health initiative - it is a bold step forward in our shared mission to secure the health and future of Papua New Guinea's youngest generation," WHO Papua New Guinea representative Dr Masahiro Zakoji said.
Last year, UNICEF highlighted Papua New Guinea's low childhood immunisation coverage.
It found only about 50 percent of children born each year received "essential life-saving vaccines", which included the oral polio vaccine. That left about 120,000 children unvaccinated each year, the agency said.
It said to prevent outbreaks and reach herd immunity against polio, vaccine coverage should be at least 95 percent.
The agency said that while the global prevalence of the disease had plummeted by more than 99 percent in the past 35 years, millions of children were still affected because they missed out on the vaccine.
Most of these children (85 percent) were living in "fragile settings", UNICEF said. These included countries and communities where there was conflict, natural disasters and humanitarian crises.
In 2000, Papua New Guinea had been declared polio-free, but 18 years later, an outbreak of vaccine-derived polio type 1 was declared. It resulted in 26 cases across nine provinces in 2018.
The US Centre for Disease Control and Prevention (CDC) said this strain is related to the weakened live polio virus used in oral polio vaccine. If allowed to circulate in populations which have low immunisation rates or are unimmunised "for long enough", or replicate in "an immunodeficient individual", the weakened virus can revert to a form that causes illness and paralysis, the CDC said.
The WHO said the 2018 Papua New Guinea outbreak was brought under control through further rounds of vaccination, community engagement and better surveillance of the disease.
Meanwhile, the current outbreak is related to vaccine-derived poliovirus type 2.
In May, Papua New Guinea's health department said the strain was a "rare form of the virus that can emerge in under-immunised communities but is well understood and can be effectively controlled through vaccination".
Correction/ Clarification:
An earlier version of this story stated the WHO said there were over 31 cases of polio in Papua New Guinea. This is incorrect under the organisation's definition of poliomyellitis or polio, which states individuals are only confirmed cases if they exhbit polio symptoms - primarily accute flaccid paralysis (the sudden onset of muscle weakness or paralysis).
