Polio

Poliovirus once paralyzed hundreds of thousands of children annually worldwide. Global vaccination efforts led by WHO, UNICEF, and partners have reduced wild poliovirus to a small number of countries, though outbreaks of vaccine-derived poliovirus can occur in under-immunized communities. Eradication requires closing the last gaps in routine and supplementary immunization, alongside sensitive surveillance for even single cases. Virus Tracker presents available regional signals to support awareness of where transmission risk persists.

Poliovirus spreads mainly through the fecal-oral route, particularly where sanitation is poor, and can also spread via contaminated food or water. It can also spread through respiratory droplets in some settings. Most infections are asymptomatic or mild, which allows the virus to circulate silently before paralytic cases are detected.

Most infected people have no symptoms or a mild flu-like illness. In a small fraction of cases, the virus invades the nervous system and causes irreversible paralysis, most often in the legs. Paralysis affecting breathing muscles can be life-threatening without medical support.

Oral and inactivated polio vaccines are safe and highly effective, and routine childhood immunization combined with supplementary campaigns is the core strategy for eradication. Maintaining high coverage prevents both wild and vaccine-derived poliovirus from finding susceptible populations to spread within.

Surveillance centers on detecting acute flaccid paralysis in children and testing stool samples, supplemented by environmental surveillance of sewage in high-risk areas. Because so few infections cause visible paralysis, a single confirmed case signals substantially wider silent circulation.

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