Polio Resurges in Papua New Guinea, Highlighting Challenges in Global Eradication Efforts

Recently, the World Health Organization (WHO) declared a polio outbreak in Papua New Guinea (PNG), marking a significant concern in the fight against this debilitating disease. The outbreak was detected after two healthy children, who had received polio vaccinations, tested positive for the virus during routine wastewater analysis in Lae, PNG's second-largest city. Elevated virus levels have also been found in wastewater samples from Port Moresby, the capital, indicating a potential spread across the country.

The strain identified is circulating vaccine-derived poliovirus type 2, genetically similar to a strain previously circulating in Indonesia. This development underscores the persistent threat posed by vaccine-derived viruses, which can mutate from weakened vaccine strains to cause paralysis, especially when vaccination rates are insufficient.

Polio, or poliomyelitis, is a highly contagious viral disease that primarily affects children and can lead to paralysis in severe cases. It spreads mainly through contact with infected persons or contaminated fecal matter. Despite widespread vaccination campaigns resulting in a 99% reduction in cases globally since the late 20th century, the disease has not been eradicated entirely. Currently, wild poliovirus remains endemic only in Pakistan and Afghanistan.

The global fight against polio relies on two main vaccines: the oral polio vaccine (OPV) and the inactivated polio vaccine (IPV). The OPV, administered orally, contains a weakened virus that boosts gut immunity but carries a small risk of reverting to forms capable of causing paralysis, leading to circulating vaccine-derived polioviruses. The IPV, given via injection, stimulates systemic immunity but is less effective at preventing transmission.

The recent outbreak in PNG has prompted rapid response actions, including mass vaccination efforts supported by partners such as WHO, UNICEF, and Australia. Unfortunately, PNG's vaccination coverage remains below the optimal 95%, with only about half of the children receiving recommended vaccines annually. This low coverage facilitates the conditions for outbreaks and virus circulation.

After being declared polio-free in 2000, PNG experienced an outbreak in 2018, with 26 cases of vaccine-derived poliovirus across nine provinces. Collaborative efforts—mass immunizations using novel vaccines, enhanced surveillance of cases and wastewater, and community engagement—successfully contained that outbreak. These strategies remain vital as PNG now faces this new threat.

Although the risk of the virus spreading to Australia is currently low, declining childhood vaccination rates since the COVID-19 pandemic pose a potential threat. Maintaining high immunization coverage, particularly in border regions and neighboring countries, is crucial. Australia's overall vaccination rate is close to 95%, but gaps in coverage and waning immunity could jeopardize its polio-free status.

Global eradication of polio remains a formidable challenge. This recent outbreak serves as a stark reminder that the fight against poliovirus is ongoing, necessitating continued global cooperation, strengthened health systems, and swift responses to emerging threats to achieve a polio-free world.