GoKawiilTen 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.
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