Story highlights

Polio was confirmed in a 6-year-old boy in May

Two more children have been diagnosed with poliovirus

The strain of poliovirus detected in the boy is now circulating in the community

(CNN) —  

A polio outbreak has been confirmed in Morobe Province of Papua New Guinea, the World Health Organization reported Monday.

Papua New Guinea had been certified polio-free since 2000, along with the rest of WHO’s Western Pacific Region.

The virus was suspected as the cause of lower limb weakness in a 6-year-old boy in Morobe Province in April; in May, the diagnosis was confirmed.

The same strain of virus was detected in stool specimens of two healthy children living in the community by the US Centers for Disease Control and Prevention, which confirmed the outbreak on Friday.

The total of three cases prompted the declaration of an outbreak.

WHO also determined that the strain of poliovirus detected in the children – vaccine-derived poliovirus type 1 – is circulating in the community.

Three provinces – Morobe, Eastern Highlands, Madang – have been identified as “most high risk,” said Dr. Mohammad Salim Reza, a WHO technical officer in Papua New Guinea. The nation’s deputy prime minister declared a “polio outbreak as National Health Emergency on 26 June and allocated 6.7 million Kina for the response,” said Reza, who added that half a million US dollars were allocated from the Global Polio Eradication Initiative to support the country.

Vaccination coverage

Poliomyelitis, known as polio, is a highly infectious viral disease that invades the brain and spinal cord and causes permanent paralysis in a small proportion of patients, including the 6-year-old in Morobe, according to WHO.

There is no cure, and the disease can be deadly. The virus, which mainly affects young children, spreads from person to person and can be transmitted through contaminated food and water.

Water, sanitation and hygiene are challenges in Morobe Province, where the boy was diagnosed with polio, and polio vaccine coverage is low there, with less than two-thirds of all children having received the recommended three doses.

The province, which is on the northern coast of Papua New Guinea, boasts a population of more than half a million people.

The National Department of Health of Papua New Guinea has been working with WHO and other partners in launching a response to the outbreak, which includes a large-scale vaccination campaign and increased health surveillance to help detect illness and the presence of the virus.

The immunization campaign, which targets children under 15 years old, has already vaccinated 845 children, according to WHO. Neighboring provinces are taking similar steps, according to the agency.

Additionally, the United Nations International Children’s Emergency Fund and WHO have conducted house-to-house surveys, sample collection and contact tracing, in addition to analyzing stool specimens from the community and family of the patient.

The immediate aim of all these efforts is to rapidly stop the circulation of the virus within communities and prevent children from becoming paralyzed, according to WHO.

What is vaccine-derived poliovirus type 1?

The oral polio vaccine contains a weakened form of the poliovirus in order to activate the body’s immune system.

When a child swallows drops of the vaccine, the weakened form of virus briefly replicates in the intestines, where antibodies begin to develop against the actual virus. During the short period when this vaccine-virus lives in the intestines, it is excreted and may spread to other people before eventually dying out if adequate sanitation is not maintained.

By coming into contact with the virus in this way, children who have not been vaccinated may “passively” develop immunity in some cases, according to WHO.

However, on rare occasions, an excreted vaccine-virus can continue to circulate within an environment for a longer than usual period while undergoing genetic changes. In such cases, the virus may morph into a form that can cause paralysis – just as the wild strain of poliovirus can.

This was the case for the young boy in Morobe.

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“WHO has been working with the Government on the investigation, laboratory confirmation, enhanced surveillance and response activities,” said Dr. Luo Dapeng, WHO representative in Papua New Guinea, in a statement. “We will continue to support the Government to ensure children are protected.”

WHO recommends that travellers to polio-affected areas be fully vaccinated against polio. Residents (and visitors for more than four weeks) should receive an additional dose of oral polio vaccine or an inactivated polio vaccine within four weeks to 12 months of travel.