Polio Is Close to Defeat, But the Last Mile Is the Most Dangerous

Global polio cases have fallen sharply, but the virus continues to survive in communities where vaccination teams struggle with conflict, insecurity, displacement and access restrictions. The latest Emergency Committee assessment under the International Health Regulations keeps international poliovirus spread classified as a Public Health Emergency of International Concern, underscoring how the final phase of eradication depends increasingly on reaching children who remain outside routine and campaign vaccination systems.

The global campaign against polio is approaching a point where progress and vulnerability increasingly exist side by side. Wild poliovirus type 1 is now endemic only in Afghanistan and Pakistan, and case numbers have fallen sharply, but transmission continues to survive in communities where conflict, insecurity, displacement and gaps in vaccination make every missed child more consequential.

The final phase of eradication is thus proving so difficult. The challenge is reaching the same hard-to-access populations repeatedly, detecting transmission quickly and preventing the virus from crossing borders or exploiting immunity gaps. Vaccine-derived outbreaks, persistent reservoirs and mounting funding pressures mean that falling case numbers cannot yet be mistaken for the end of the emergency.

Fewer Cases Do Not Mean the Virus Is Cornered

Only four WPV1 cases had been reported in 2026 at the time of the assessment, three in Afghanistan and one in Pakistan, compared with 52 during 2025. Environmental surveillance also recorded a steep fall, from 747 positive samples in 2025 to 74 in 2026, suggesting that circulation has contracted sharply.

However, the virus survived the recent low-transmission season, with southern Afghanistan, South Khyber Pakhtunkhwa and Karachi remaining important reservoirs. That persistence is critical because eradication requires every transmission chain to disappear, not simply for national or global case totals to fall.

This makes the final stage fundamentally different from earlier phases of the campaign. When transmission is widespread, expanding overall coverage can drive large gains; when it becomes concentrated, a relatively small number of repeatedly missed communities can determine whether the virus survives.

Afghanistan demonstrates the difficulty. House-to-house vaccination campaigns stopped in October 2024 because of security concerns, leaving the programme dependent on site-to-site vaccination, while the limited number of women in vaccination teams creates an additional barrier to reaching some young children.

Eradication Now Depends on the Children Health Systems Miss

Pakistan faces a different version of the same problem. National and provincial vaccination coverage has been strong, but performance remains uneven at district level, particularly in areas affected by insecurity; around 250,000 children in South Khyber Pakhtunkhwa were reportedly not reached.

High overall coverage can coexist with persistent transmission if the same populations are repeatedly missed, meaning averages become less informative precisely when the programme gets closest to its goal.

The problem extends far beyond Afghanistan and Pakistan. More than 4.5 million children under five in northern Yemen remain susceptible amid insecurity and access restrictions, while more than 450,000 children have been missed during campaigns in southern and central Somalia; Nigeria also continues to struggle to reach every child in high-risk northern areas.

This overlap between humanitarian vulnerability and vaccination gaps is increasingly shaping the geography of polio. The hardest places to eliminate the virus are no longer simply those with weak vaccination systems, but those where conflict, displacement and restricted access repeatedly interrupt the basic ability to deliver vaccines.

Better Vaccines Cannot Solve an Access Problem Alone

Vaccine-derived poliovirus remains another major obstacle, although recent numbers have also improved. As of 30 April 2026, 32 circulating vaccine-derived poliovirus cases and 27 positive environmental detections had been reported across 12 countries, compared with 238 cases and 247 environmental detections across 30 countries in 2025.

There are encouraging signs from novel oral polio vaccine type 2, or nOPV2, which has shown greater genetic stability and a much lower risk of reverting toward neurovirulence than the older Sabin OPV2. More than two billion doses have been administered since 2021, and more than 80% of affected countries have stopped cVDPV2 outbreaks with three or fewer supplementary immunization activities using nOPV2.

However, the persistence of outbreaks points to the limits of relying on vaccine technology alone. The remaining transmission is strongly linked to inaccessible communities, insecurity, displacement and large numbers of zero-dose or under-immunized children, meaning the problem is increasingly one of delivery rather than simply product performance.

Nigeria underscores that tension. It accounted for 14 cVDPV2 cases, half of the global cVDPV2 caseload recorded at that stage of 2026, while simultaneously confronting cVDPV2 and cVDPV3 outbreaks.

The Last Mile May Be Won or Lost on Surveillance and Funding

The closer polio gets to eradication, the more important surveillance becomes. When cases are rare, health systems must be able to detect isolated transmission quickly through environmental sampling, laboratory networks and rapid investigation before an unnoticed chain spreads into areas with immunity gaps.

The need is now colliding with a financial problem. The Emergency Committee warned that a funding shortfall estimated at nearly 30% threatens essential elements of the eradication programme, including sensitive surveillance systems, while rising transport and fuel costs and wider pressure on international health financing are making operations more expensive.

International movement makes any weakening of surveillance more consequential. Genetic analysis documented at least 13 international cVDPV importation events between January 2025 and January 2026, while WPV1 was detected in wastewater in Germany in October 2025: a reminder that countries without endemic transmission are not insulated from imported virus.

The polio endgame is becoming less about the headline number of cases and more about the resilience of the systems surrounding them. Routine immunization, cross-border coordination, vaccination of mobile populations, laboratory capacity and sustained financing now matter precisely because transmission has become so concentrated.