Reemergence of polio points to difficulties in national vaccine coverage

Papua New Guinea (PNG) is once again grappling with a polio outbreak, a significant public health concern that has prompted an urgent response from national authorities and international partners.

The World Health Organization (WHO) officially declared an outbreak on May 9, 2025, following the detection of circulating vaccine-derived poliovirus type 2 (cVDPV2) in stool samples from two healthy children in Lae, Morobe Province. This detection was preceded by the presence of the virus in environmental surveillance (wastewater) samples from both Lae and Port Moresby, indicating community transmission.

Polio strain

The current cVDPV2 strain is genetically linked to one circulating in Indonesia, highlighting the persistent risk of cross-border transmission. Vaccine-derived polioviruses can emerge in populations with low immunization coverage, as the weakened virus in the oral polio vaccine (OPV) can circulate and mutate, regaining the ability to cause paralysis. PNG had been declared polio-free since 2000, with a previous outbreak in 2018 successfully contained.

A major contributing factor to this resurgence is PNG’s suboptimal routine immunization coverage.

As of 2024, national vaccination coverage for the third dose of oral polio vaccine (OPV3) was a concerning 44%. In Morobe province, where the recent cases were identified, coverage with bivalent OPV (bOPV) has remained below 40% over the past five years, ranging from 28-37%. While Lae city shows higher coverage (73% for bOPV), significant pockets of under-immunized children exist across the country, with some districts reporting coverage as low as 8%. To achieve herd immunity and prevent outbreaks, vaccination coverage should ideally be at least 80% and preferably 95%.

Response to polio outbreak

In response, the National Department of Health (NDoH) and Provincial Health Authorities (PHAs) have activated their emergency operations centers and are intensifying surveillance efforts, including active searches for cases of Acute Flaccid Paralysis (AFP), a key indicator of polio.

The government has allocated 13 million Kina (approximately US$3.19 million) to support surveillance and routine immunization activities. Plans are being finalized for nationwide vaccination campaigns targeting children under ten years old, utilizing the novel oral polio vaccine (nOPV2), which is considered less likely to mutate.

Despite the immediate concern, health experts emphasize that the situation is “serious but manageable,” drawing on lessons learned from the successful containment of the 2018 outbreak.

However, challenges remain, including geographical inaccessibility to remote communities, vaccine hesitancy, and the need to strengthen overall health systems. International partners like WHO, UNICEF, and the Australian government are providing crucial support to PNG’s vaccination rollout and community engagement efforts, including combating misinformation. The collective focus is on rapidly increasing immunization rates to protect all children and prevent further spread of the virus.