Polio spreads from person to person, primarily when the virus from an infected person’s stool reaches another person’s mouth. This fecal-oral route is the dominant transmission pathway, though the virus can also spread through respiratory secretions. Once swallowed, poliovirus enters through the mouth, multiplies in the throat and intestinal tract, and can be shed for weeks, making infected individuals contagious long before (and after) they show any symptoms.
The Fecal-Oral Route
The most common way poliovirus moves between people is through fecal contamination. An infected person sheds large quantities of the virus in their stool for three to six weeks after infection. In places with poor sanitation, the virus easily finds its way into water supplies, onto food, and onto surfaces. When someone drinks contaminated water, eats contaminated food, or touches a contaminated surface and then touches their mouth, the virus enters their body and the cycle starts again.
This is why polio has historically thrived in communities without reliable sewage treatment or clean drinking water. Even small amounts of fecal matter, invisible to the naked eye, can carry enough virus to cause infection. Children playing in areas with open sewage, shared water sources without treatment, and inadequate handwashing all create opportunities for the virus to spread. The World Health Organization identifies contaminated water and food as common vehicles for transmission alongside direct person-to-person contact.
Spread Through Throat Secretions
Poliovirus also replicates in the throat, which means it can spread through saliva, coughing, and sneezing. The virus is present in nasopharyngeal secretions for one to two weeks after infection. This oral-oral route plays a more significant role in areas with better sanitation, where fecal contamination of water is less likely. Close contact with an infected person, sharing utensils, or being coughed on can all transmit the virus this way.
Why Infected People Spread It Without Knowing
One of the most important things to understand about polio transmission is that the vast majority of infected people never develop obvious symptoms. They feel fine, or perhaps slightly under the weather, but they are still shedding virus in their stool and throat secretions for days or weeks. These individuals move through their communities, using shared bathrooms, preparing food, and interacting with others, all while unknowingly spreading the virus. This silent transmission is what made polio so difficult to contain before vaccines existed, and it’s why even a single confirmed case in a community signals widespread circulation.
The incubation period for mild symptoms is 3 to 6 days after exposure. If the infection progresses to paralysis, that typically begins 7 to 21 days after infection. But a person becomes contagious before symptoms appear and remains contagious for weeks afterward, creating a long window during which they can infect others.
What Happens Inside the Body
After entering through the mouth, poliovirus multiplies in two places: the throat and the intestines. During this intestinal replication, the virus invades nearby lymph tissue. In most people, the immune system contains it there, and the infection resolves without incident. In a smaller number of cases, the virus breaks through into the bloodstream. From there, it can reach the central nervous system and attack the nerve cells that control muscle movement, which is what causes paralysis.
The virus persists in the intestines far longer than in the throat. While throat shedding lasts about one to two weeks, stool shedding continues for three to six weeks. This extended intestinal shedding is the primary engine of transmission in communities.
Vaccine-Derived Transmission
There is a second, less intuitive way polio can circulate. The oral polio vaccine (used widely in developing countries because it’s inexpensive and easy to administer) contains a weakened, live form of the virus. A vaccinated child sheds this weakened virus in their stool, which can actually help immunize others in the community through indirect exposure. But if the weakened virus circulates long enough in a population where too few people are vaccinated, it can genetically revert and regain the ability to cause paralysis. These are called circulating vaccine-derived polioviruses.
This happens exclusively in communities with very low vaccination rates. When enough people are immunized, the weakened virus encounters immune individuals and stops circulating before it can mutate. When immunization gaps exist, the virus has room to keep spreading and evolving. This is why maintaining high vaccination coverage matters even in areas that haven’t seen a case in years.
Where Polio Still Spreads
Wild poliovirus type 1 is the only remaining wild strain, and as of early 2026, it is endemic in just two countries: Afghanistan and Pakistan. In the first few months of 2026, four confirmed cases of wild poliovirus type 1 were reported (three in Afghanistan, one in Pakistan), along with 68 detections in environmental surveillance samples like sewage. These environmental detections confirm the virus is circulating more widely than case counts alone suggest.
Wild poliovirus types 2 and 3 have been eradicated. However, vaccine-derived poliovirus outbreaks have occurred in parts of Africa, the Middle East, and Southeast Asia in recent years, always linked to communities with insufficient immunization coverage.
What Raises Your Risk
The single biggest risk factor for getting polio is being unvaccinated. Beyond that, the risk depends heavily on environment and circumstances. Living in or traveling to areas where poliovirus circulates, lacking access to clean water and sanitation, and living in crowded conditions where hygiene is difficult all increase the chance of exposure. Young children are most vulnerable because they are more likely to come into contact with contaminated surfaces and put their hands in their mouths.
Poliovirus is also resilient in the environment. It survives in water and sewage for extended periods, outlasting common bacterial indicators that water treatment systems often monitor. This environmental persistence means the virus can linger in contaminated water sources long after an infected person has moved on, creating ongoing exposure risk for anyone using that water without adequate treatment.