Polio: The Disease the World Almost Ended and Why It Is Not Over Yet

This informal CPD article ‘Polio: The Disease the World Almost Ended and Why It Is Not Over Yet’ was provided by Cima Care, who offer extensive training in vaccination and public health, advancing global health initiatives.

Few accomplishments in modern medicine come as close to a happy ending as the story of polio. A disease that once paralysed hundreds of thousands of children every year has been pushed to the very edge of extinction. And yet, decades into the effort, the world has still not quite crossed the finish line. Understanding why and what it will take to get there offers a rare window into how global health really works: the breakthroughs, the setbacks, and the quiet, careful operational work that keeps a nearly vanished virus from returning. ^{1 & 18}

A Rare Public Health Triumph 

The progress has been genuinely impressive. Polio cases have decreased by more than 99% since a coordinated global eradication effort started in 1988, preventing an estimated 20 million cases of paralysis in children. ¹ To put that in perspective: in 1988 there were around 350,000 recorded cases of wild poliovirus worldwide; by 2021, that number had fallen to just six. ² Progress on that scale is almost unheard of in an infectious disease.

So Why Isn't Polio Gone? 

If cases have dropped by more than 99%, why does polio remain a global health priority? The answer lies in that stubborn final fraction. According to a report in 2024, Afghanistan and Pakistan remain the only two countries where wild poliovirus is still endemic. This means it has never been fully stopped there. By mid-June 2024, the two countries had reported a total of five new cases of the main wild strain, broadly in line with the total recorded the year before. ^{3 & 21} As long as the virus stays anywhere, it can travel across borders, and children who are not protected remain at risk. 

There is also a second, less regular challenge, known as vaccine-derived poliovirus (A rare poliovirus that starts from the weakened virus in the oral polio vaccine and, when it spreads for long periods in under‑immunised communities, mutates back into a form that can cause paralysis). During 2024, several countries, mainly in Africa, reported cases of this type. ^{4 & 19} In 2022, some countries even experienced more than one type of poliovirus circulating at the same time. ⁵ The encouraging news is that the overall trend has been lowered: cases linked to vaccine-derived poliovirus fell from 881 in 2022 to 524 in 2023. ⁶

A Newer Tool in the Kit

Science has been adapting in response. A newer oral polio vaccine, designed to be more genetically stable than the earlier version, has shown assurance in decreasing the risk of vaccine-derived cases. Between March 2021 and December 2023, around one billion doses were administered across 35 countries. ⁷

Clues in the Sewage: Tracking a Hidden Virus

One of the most attention-grabbing tools in the fight against polio does not involve patients at all. It involves wastewater. Because the virus is shed in human waste, testing sewage can show that poliovirus is circulating silently in a community well before anyone gets sick, giving public health teams a helpful head start. 

The results can be striking. In 2022, genetic testing confirmed the presence of poliovirus in 100 sewage samples collected across several counties in New York State. ⁸ In more than 1,000 samples collected from dozens of sewer systems, 89 samples, about 8%, from just one county tested positive for poliovirus type 2. ⁹ Aroundthe same period, Canada reported vaccine‑derived poliovirus type 2 in two wastewater samples collected in August 2022 from areas closely connected to New York communities where the virus had also been detected. ¹⁰ 

Findings like these are a reminder that poliovirus can be detected even in places far from where it still spreads freely. Recognising the value of this early-warning approach, countries in the region have expanded it: over two years, 15 new wastewater surveillance sites were added in the affected countries. ¹¹

The Economic Case for Finishing the Job

Ending polio is not only a medical goal; it also makes financial sense. A 2024 investment case for eight priority countries in the Eastern Mediterranean Region estimated economic and social advantages of about US$289.2 billion from sustaining and repurposing polio assets, against baseline costs of US$7.5 billion. In practical terms, that represents a return of nearly US$39 for every US dollar invested overall, including about US$38.70 for each dollar spent on expanding immunisation programmes and US$36.40 for every dollar invested in strengthening surveillance and emergency response. ¹²

Reaching the Very Last Child

The hardest part of any eradication effort is almost always the final stretch: reaching the children who have been missed. Here, technology is increasingly enabling. Geographic mapping tools can improve both coverage and fairness by identifying overlooked settlements and the children who have received no vaccine doses at all, allowing planners to direct resources to where they are needed most. ^{13 & 14} Mobile technology plays a growing role too, particularly in remote areas, by enhancing how data is collected, how campaigns are designed, and how information reaches the communities that need it. ^{15 & 16}  

Staying Watchful

Perhaps the most influential lesson of the polio story is that progress, however significant, is not the same as fulfillment. Quick reporting of any suspected case to public health authorities remains a cornerstone of the surveillance systems that keep outbreaks in check. ¹⁷ Maintaining high routine vaccination rates and supporting open, well-informed conversations about vaccines are what allow hard-won progress to be maintained. 

The world stands closer to ending polio than it has ever been. Crossing that final line will depend not on any single breakthrough, but on the steady combination of vaccination, watchful surveillance, and continued innovation that has brought the goal within reach. ²⁰

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2- The U.S. Government and Global Polio Efforts [Internet]. The Henry J. Kaiser Family Foundation. 2019. Available from: https://www.kff.org/global-health-policy/fact-sheet/the-u-s-government-and-global-polio-efforts/

3- Center for Infectious Disease Research and Policy [Internet]. Umn.edu. 2024 [cited 2024 Oct 15]. Available from: https://www.cidrap.umn.edu/polio/afghanistan-pakistan-report-more-wild-poliovirus-cases

4- Center for Infectious Disease Research and Policy [Internet]. Umn.edu. 2024 [cited 2024 Oct 15]. Available from: https://www.cidrap.umn.edu/polio/seven-countries-report-more-polio-cases-including-wild-type-afghanistan

5- Lee SE. Progress toward poliomyelitis eradication-worldwide, January 2021–March 2023. MMWR. Morbidity and Mortality Weekly Report. 2023;72.

6- Geiger K. Progress Toward Poliomyelitis Eradication-Worldwide, January 2022–December 2023. MMWR Morbidity and Mortality Weekly Report [Internet]. 2024;73. Available from: https://www.cdc.gov/mmwr/volumes/73/wr/mm7319a4.htm

7- Kurji FD, Bandyopadhyay AS, Zipursky S, Cooper LV, Gast C, Toher M, Clemens R, Clemens SA, Prasad R, Azhari A. Novel oral polio vaccine type 2 use for polio outbreak response: A global effort for a global health emergency. Pathogens. 2024 Mar 23;13(4):273.

8- Polio Wastewater Surveillance [Internet]. Available from: https://www.health.ny.gov/diseases/communicable/polio/wastewater.htm

9- Ryerson AB. Wastewater Testing and Detection of Poliovirus Type 2 Genetically Linked to Virus Isolated from a Paralytic Polio Case-New York, March 9–October 11, 2022. MMWR Morbidity and Mortality Weekly Report [Internet]. 2022;71. Available from: https://www.cdc.gov/mmwr/volumes/71/wr/mm7144e2.htm

10- Center for Infectious Disease Research and Policy [Internet]. Umn.edu. 2023 [cited 2024 Oct 15]. Available from: https://www.cidrap.umn.edu/polio/canada-detects-poliovirus-wastewater-samples

11- GPEI-Timely outbreak response, enhanced surveillance halts wild poliovirus transmission in Southern Africa [Internet]. Polioeradication.org. 2024 [cited 2024 Oct 15]. Available from: https://polioeradication.org/news/timely-outbreak-response-enhanced-surveillance-halts-wild-poliovirus-transmission-in-southern-africa/

12- Administrator. Sustaining polio investments offers a high return [Internet]. World Health Organization-Regional Office for the Eastern Mediterranean. 2023 [cited 2024 Oct 15]. Available from: https://www.emro.who.int/polio-eradication/news/sustaining-polio-investments-offers-a-high-return.html

13- Chaney SC, Mechael P, Thu NM, Diallo MS, Gachen C. Every Child on the Map: A Theory of Change Framework for Improving Childhood Immunization Coverage and Equity Using Geospatial Data and Technologies. Journal of Medical Internet Research. 2021 Aug 3;23(8):e29759.

14- GIS Mapping Evidence Brief: Evidence on pro-equity interventions to improve immunization coverage for zero-dose children and missed communities [Internet]. Available from: https://zdlh.gavi.org/sites/default/files/2023-09/6._evidence_brief_gis.pdf

15- Oliver-Williams C, Brown E, Devereux S, Fairhead C, Holeman I. Using mobile phones to improve vaccination uptake in 21 low- and middle-income countries: systematic review. JMIR mHealth and uHealth. 2017 Oct 4;5(10):e7792.

16- The Use of Digital Technologies and Approaches for Real-Time Monitoring of Supplementary Immunization Activities: Good practices and lessons learned [Internet]. Available from: https://www.unicef.org/media/93781/file/gavi-unicef-digital-technology-immunization-2021.pdf

17- CDC. Clinical Guidance for Investigating a Suspected Case of Polio [Internet]. Polio. 2024. Available from: https://www.cdc.gov/polio/hcp/reporting-suspected-cases/index.html

18- Polio Eradication Strategy 2022-2026 [Internet]. Who.int. 2022 [cited 2026 July 20]. Available from: https://www.who.int/publications/b/57914

19- World Health Organization. Vaccine-derived poliovirus (VDPV) factsheet. Geneva: WHO; 2017. Available from: https://www.who.int/docs/default-source/documents/gpei-cvdpv-factsheet-march-2017.pdf

20- Pan American Health Organization. Polio Bulletin, Year 40, Nos. 27–28: WUENIC 2024-What latest immunization estimates mean for polio eradication [Internet]. Washington (DC): PAHO; 2025 Jul 12 [cited 2026 Jul 19]. Available from: https://www.paho.org/en/documents/polio-bulletin-year-40-27-28-12-july-2025

21- Global Polio Eradication Initiative. GPEI-Homepage [Internet]. Global Polio Eradication Initiative. 2024 [cited 2026 July 20]. Available from: https://polioeradication.org/