Ten years ago, the virus that causes polio seemed to be on its way to extinction. In August 2016, Nigeria experienced its last two cases of the wild virus, leaving it circulating only in Afghanistan and Pakistan. Amid global excitement, Hamid Jafari, who at the time directed polio operations and research at the World Health Organization (WHO) predicted of Pakistan: “We may be looking at months — months, not years — before we eradicate polio in this country”.
Polio is on the brink of eradication. Here’s how to keep it from coming back
Since then, however, eradication targets have come and gone: 2019, 2023, 2025. Last month was the latest missed target to stop transmission. In the past decade, more than US$3 billion has been spent fighting the virus in Afghanistan and Pakistan, where billions of doses of oral vaccine have been administered. Campaign leaders hoped that polio would finally disappear during last winter’s low-transmission season. But that didn’t happen; 14 new cases have been reported so far this year.
Fresh challenges now threaten the endgame, such as an unprecedented funding shortfall, and, from New York to rural Pakistan, a growing hesitancy towards vaccines.
Although the WHO said last January that eradication was “within reach”, most researchers interviewed by Nature for this article are very concerned about the chances of success. “In theory, eradication is possible, but in practice, it is not,” says Kimberly Thompson, who studies health economics at Kid Risk, a non-profit consultancy in Orlando, Florida, that models polio transmission and eradication.
So will we ever rid the world of polio, or is it time for plan B?
Ambitious effort
The effort to eradicate polio relies on the oral polio vaccine (OPV) — a drop of liquid containing live, attenuated poliovirus. Giving it to children both protects them from disease and stops the virus from spreading by blocking its replication in the gut. A population immunity level of about 90% is needed in vulnerable areas for the virus to peter out. A different vaccine, the inactivated polio vaccine (IPV), contains killed strains and is given as an injection. It is administered globally, in both vulnerable and polio-free areas, and protects against disease but doesn’t stop transmission.
In rare cases, the attenuated virus in OPV can mutate to regain virulence, meaning that it can lead to cases of vaccine-derived polio and paralysis. Where immunity is poor, vaccine-derived polio can spread through communities. Ultimately, the strategy is to eradicate wild poliovirus with oral vaccine and then to carefully withdraw that vaccine without triggering vaccine-derived polio, while using IPV to insure against such outbreaks.
On the face of it, the approach is working well. When the Global Polio Eradication Initiative (GPEI) began nearly 40 years ago, there were 350,000 cases of wild polio each year across 125 countries. By 2025, the GPEI, a partnership of national governments and international organizations, had reduced wild polio to a mere 52 new cases — a 99.98% drop. What’s more, modellers calculate that its work has prevented between 2.5 million and 6 million cases of paralysis1.
And leaders still say they are upbeat. At present, says Arshad Quddus, acting director of the GPEI, progress is still being made towards zero: polio is transmitted less often and in smaller areas. Some places previously regarded as ‘core reservoirs’ have seen no cases in more than a year, he adds.
But the data tell a different story: polio cases rise and fall. For example, the number of wild cases dipped to 22 in 2017 but rose to 176 in 2019, fell to 6 in 2021 but rebounded to 99 in 2024 (see ‘Highs and lows’). The pattern is similar for detection of the virus in the environment. It’s enough for Thompson to conclude: “We’re not heading towards success.”
Source: World Health Organization
The key to polio eradication is high population immunity, particularly gut immunity, which blocks transmission. It has been achieved in the most difficult of geographies: now, of the three types of wild polio that used to circulate, only type 1 remains.
If the rest of the world has managed to stop transmission, why isn’t that happening in the two remaining hide-outs? Is there something about type 1 that makes it harder to quash than the others? “The answer to that, I think, has to be no,” says David Salisbury, chair of the GPEI’s Global Commission for Certification of Poliomyelitis Eradication, citing its successful eradication elsewhere. Some researchers have suggested that the oral vaccine is failing to trigger the level of immunity in Afghanistan and Pakistan that it did elsewhere2, but most say that the problem is not a scientific one.
“We know the tools, we know the key reservoir areas,” says Isobel Blake, who models polio epidemiology at Imperial College London. The challenges, she says, are “operational”.
Despite Herculean efforts, there remain 100,000 unvaccinated children in inaccessible districts of the two countries, and average immunization rates in some districts are below 50%, says Zulfiqar Bhutta, a paediatrician at Aga Khan University in Karachi, Pakistan. And yet much of what they face has been dealt with in other parts of the world, says Salisbury.
This year, violence erupted between Pakistan and Afghanistan, and conflict-ridden areas in south Pakistan have become unreachable, says Quddus; many people continually cross the border between Pakistan and Afghanistan, replenishing viral reservoirs, and mistrust of vaccinators has grown. At least four police guards have been killed while accompanying vaccinators just this year in Pakistan, and in south Afghanistan, female and house-to-house vaccinators, who have been crucial to global success, are banned.
Yet in northeast Nigeria, Salisbury says, polio was eradicated despite the rebel group Boko Haram actively resisting polio campaigns between 2009 and 2016, killing vaccinators and destroying health facilities. And the war in Gaza did not prevent negotiation in 2024 of a humanitarian pause to allow emergency polio vaccination of 640,000 children. Religious opposition, too, has been overcome in other places, he says.
Polio is on the brink of eradication. Here’s how to keep it from coming back
But Quddus maintains that some problems in Afghanistan and Pakistan are unique. In Gaza, it’s clear who is in conflict and from whom to seek approval for a campaign. But in the southern part of the Khyber Pakhtunkhwa province in northwest Pakistan, “it’s a messy situation. There’s not a very specific group or groups” to negotiate with. And in south Afghanistan, concedes Salisbury, the prohibition on house-to-house and female vaccinators is “a fundamental difficulty”.
Polio workers are constantly innovating in these regions, says Quddus. “What is abundantly clear,” says Kathleen O’Reilly, an epidemiologist at the London School of Hygiene & Tropical Medicine and WHO polio adviser, “is that they will try anything and everything”.
There are some challenges making today’s campaign even more difficult. The novelty of this global mission has waned; polio cases are rarer than other health problems, which erodes communities’ enthusiasm for vaccination. Polio funding flows to the Afghan authorities “no matter how badly the programme is run”, the GPEI’s Independent Monitoring Board noted last year. “For the first time in the history of polio eradication, it does not feel as if Afghanistan is, or wants to be [involved].”
Falling funds
The other major issue is that the campaign has had to contend with a 30% budget cut this year. The upheaval in US engagement with global health is partly responsible. There remains support in the United States for polio eradication, both among the public and in Congress, and the disease was one of a small number to make it into the country’s new global-health strategy, published last year.
But changes over the past year or so — including the US withdrawal from the WHO and the dismantling of the US Agency for International Development under the administration of President Donald Trump — have disrupted the infrastructure and technical expertise that the United States contributed towards eradication.
Instead, the United States has brokered bilateral health agreements with 34 countries that receive US global-health assistance, but it is unclear how much support these will provide for polio campaigns.
A health worker administers a polio vaccine to a child in Pakistan, one of two countries where wild poliovirus cases persist.Credit: Muhammad Sajjad/AP via Alamy
Other nations, such as the United Kingdom, have ceased their contributions to the GPEI, although the Gates Foundation, a non-profit organization in Seattle, Washington, and other donors pledged $1.2 billion last December, reducing the shortfall over the next few years.
Because of the reduction to its budget, the GPEI has cut back on some of its activities — most notably OPV immunization in areas that are not currently experiencing outbreaks. Modellers say that this is risky for areas vulnerable to wild or vaccine-derived polio.
Cases of vaccine-derived polio have been dropping year on year since 2022, when there were 882 cases, mostly in sub-Saharan Africa. Case numbers surged as a result of a botched alteration to the global vaccine programme in 2016, when the type 2 oral vaccine was discontinued, after that strain was eradicated3. Quddus says that the recent fall is due to rapidly ramping up vaccination in areas affected by outbreaks.
But both Blake’s and Thompson’s models show that, to successfully stamp out outbreaks, it is essential to pre-emptively vaccinate in vulnerable populations that are currently polio-free — the very activity that has been scaled back this year.
Uncertain future
No one Nature interviewed for this article said that eradication is impossible — in theory. But most did not think it was imminent, and many thought it could not be achieved with business-as-usual approaches.
“If the programme did everything right and resources were not an issue, then it could be done,” says Thompson. But after so many years of missed targets, and in the current funding climate, she says, “I think it has already failed.”
