
Resolution Criteria
This market resolves YES if there are at least five confirmed cases of polio (either wild poliovirus or vaccine-derived poliovirus) in the United States during the 2025 calendar year.
Background
The United States has been officially polio-free since 1979, when the last case of wild poliovirus was reported. However, in recent years, there have been concerning developments:
In 2022, a case of vaccine-derived poliovirus was identified in New York state, and subsequent wastewater surveillance detected poliovirus in multiple counties
Vaccination rates have declined in some communities, creating potential vulnerability to outbreaks
Globally, polio remains endemic in Afghanistan and Pakistan, with recent outbreaks in countries like Malawi and Mozambique
Considerations
The U.S. primarily uses inactivated poliovirus vaccine (IPV), which prevents disease but doesn't stop transmission as effectively as the oral vaccine
CDC and public health authorities maintain surveillance systems to detect poliovirus in wastewater and clinical samples
For context, a comeback of five or more cases would represent a significant public health event, as the U.S. has averaged zero indigenous cases for over four decades