Polio should have been eradicated by now. What’s plan B?
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Polio should have been eradicated by now. What’s plan B?
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Female health workers are a crucial part of polio-vaccination campaigns, but have been banned in parts of Afghanistan. Credit: Shahzaib Akber/EPA-EFE/Shutterstock
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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”.<br>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.<br>Fresh challenges now threaten the endgame, such as an unprecedented funding shortfall, and, from New York to rural Pakistan, a growing hesitancy towards vaccines.<br>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.<br>So will we ever rid the world of polio, or is it time for plan B?<br>Ambitious effort<br>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.<br>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.<br>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.<br>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.<br>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.”<br>Source: World Health Organization<br>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.<br>If the rest of the world has managed to stop transmission, why isn’t...