A person who is infected can spread polio about 7-10 days before symptoms begin. A person can continue to spread the disease for about three to six weeks after the beginning of symptoms. However, a person is most contagious for the 7-10 days after symptoms have begun.
Following transmission, a person does not immediately become sick. Once the poliovirus enters the body, it travels to the back of the throat, nose, and intestines, where it begins to multiply. It can also travel to other parts of the body. After 7-14 days (on average), symptoms can begin. This period between transmission and the beginning of signs and symptoms is called the incubation period. The incubation period can be as short as 4 days or as long as 35 days.
Up to 95 percent of people who are infected have no symptoms. However, infected people who do not have symptoms can still spread the virus and cause others to develop the disease.
If a person does develop symptoms, the symptoms can be categorized into one of three groups, which include:
- Minor polio symptoms (also known as abortive poliomyelitis)
- Aseptic meningitis
- Paralytic poliomyelitis.
(Click Polio Symptoms for more information or Polio Pictures to see the possible impact of an infection with the virus.)