Polio never fully went away. Wild poliovirus still circulates in two countries, Pakistan and Afghanistan, where 99 cases were reported in 2024 and 28 more through mid-September 2025. Meanwhile, a different form of poliovirus linked to older vaccines has caused outbreaks in 39 countries since January 2023, mostly across Africa and parts of the Middle East. So while polio is not “back” in the way a new pandemic might be, it remains a persistent global threat that has proven remarkably difficult to finish off.
Where Wild Poliovirus Still Exists
Pakistan and Afghanistan are the only two countries where wild poliovirus type 1 (the original, naturally occurring virus) continues to spread. Pakistan reported 24 cases in the first nine months of 2025, while Afghanistan reported 4. That follows a difficult 2024, when the two countries combined for 99 cases, a significant jump from years when the count dipped into single digits. Conflict zones, mobile populations, and pockets of vaccine refusal keep giving the virus room to circulate in border regions between the two countries.
No other country has reported a case of wild poliovirus in years. The global eradication campaign has eliminated two of the three wild poliovirus types entirely. Only type 1 remains, and it is confined to a shrinking but stubborn geographic pocket in South Asia.
Vaccine-Derived Outbreaks Are the Bigger Story
The more widespread problem involves a form of the virus that originates from the oral polio vaccine itself. The traditional oral vaccine uses a weakened live virus. In communities with very low vaccination rates, that weakened virus can circulate from child to child through contaminated water, slowly mutating over months until it regains the ability to cause paralysis. These are called circulating vaccine-derived polioviruses.
Between January 2023 and June 2024, 74 separate outbreaks of vaccine-derived poliovirus were detected across 39 countries, producing 672 confirmed paralysis cases. The vast majority were in sub-Saharan Africa, including the Democratic Republic of the Congo, Nigeria, Ethiopia, and Chad. Outbreaks were also detected in Yemen, Somalia, Sudan, Egypt, Indonesia, and Israel. Almost all of these involve type 2, a strain that was eliminated in the wild but continues to emerge from older vaccines.
This is an ironic and frustrating situation: the tool used to fight polio is, in specific conditions, creating new outbreaks. It happens only where vaccination coverage has fallen so low that too few children are protected, giving the weakened vaccine virus an opportunity to spread and mutate. In well-vaccinated communities, this doesn’t occur.
The Gaza Outbreak
In August 2024, a ten-month-old child in Gaza was paralyzed by vaccine-derived poliovirus, the first polio case in the territory in 25 years. The ongoing conflict had devastated water and sanitation infrastructure and disrupted routine childhood vaccinations, creating exactly the conditions polio exploits.
Two emergency vaccination rounds followed in September and October 2024, reaching over 95% of targeted children despite the conflict. No additional cases have been reported since that single paralysis case, but the WHO planned further rounds into 2025 to maintain protection.
What Happened in the US and UK
In July 2022, a young adult in Rockland County, New York, was paralyzed by vaccine-derived poliovirus. It was the first US polio case in nearly a decade. The patient was unvaccinated. Subsequent wastewater testing found poliovirus in sewage samples from Rockland County, Orange County, and New York City collected between May and August 2022, suggesting limited community transmission among unvaccinated individuals.
Around the same time, London’s sewage surveillance system detected more than 100 different infectious poliovirus samples between February and November 2022, concentrated in North and East London. No paralysis cases were identified in the UK, but the sustained detection triggered emergency vaccination campaigns targeting children in affected areas. By November 2022, the virus was no longer being detected in London’s wastewater.
Both situations followed the same pattern: vaccine-derived poliovirus found its way into communities with pockets of under-vaccination. In well-immunized populations, these introductions burn out quickly. In neighborhoods where vaccine uptake has slipped, they can gain a foothold.
Why It’s So Hard to Eradicate
Polio needs about 80% vaccination coverage in a community to prevent transmission. That’s a lower bar than measles, which requires around 95%. But maintaining that coverage everywhere on Earth, year after year, in the middle of wars, displacement, and vaccine hesitancy, has proven extraordinarily difficult.
The Global Polio Eradication Initiative, the partnership driving the campaign, recently extended its target date for ending all poliovirus transmission from 2026 to 2029. The original goal was set for 2000. Every extension reflects the same reality: polio is easy to control in stable, well-resourced countries but nearly impossible to root out of conflict zones and areas with fragile health systems.
A newer version of the oral vaccine has been designed to address the vaccine-derived outbreak problem. After roughly 111 million doses were administered in seven countries during an initial rollout, genetic sequencing confirmed that the modified vaccine virus is far more stable than the older version, meaning it is much less likely to mutate back into a form that can cause paralysis. This newer vaccine is now being deployed more broadly in outbreak responses.
What This Means for Travelers
The CDC currently lists nearly 40 countries and territories where poliovirus is circulating, ranging from Pakistan and Afghanistan to several countries in West and Central Africa, plus Gaza, Indonesia, and a handful of European nations where environmental detections have occurred (including the UK, Germany, Finland, Spain, and Poland). Adults who completed their childhood polio vaccination series and are traveling to any of these destinations can get a single lifetime booster of the inactivated polio vaccine before they go.
For most people living in countries with high vaccination rates, the personal risk of polio remains extremely low. The childhood vaccine series provides strong, long-lasting protection. The concern is not that polio will sweep through well-vaccinated nations. It’s that every community with low vaccine uptake, whether in Karachi or Brooklyn, offers the virus an opening. Polio isn’t back in any dramatic sense, but it never left, and it won’t disappear until the last chains of transmission are broken.