Polio is caused by polioviruses, classified into types 1, 2 and 3. Humans are the only reservoir of infection: the poliovirus is found in the bowel and in the throat of infected individuals. Transmission occurs via the oral-faecal route or contact with saliva.

Most infections remain completely without symptoms, while 10% of cases develop mild symptoms only, such as fever, malaise, nausea, and vomiting. However, after exposure and an incubation period of about one to two weeks the virus can spread from the digestive tract to the central nervous system, resulting in meningitis and neural damage with paralysis (the latter in less than 1% of cases). No specific therapy is available against the virus.

Childhood immunisation programmes with live weakened oral poliovirus vaccine (OPV) or with inactivated, injectable poliovirus vaccine (IPV) has been very effective. On the European continent, the last case of paralysis caused by polio was reported from Turkey in November 1998. In June 2002, the WHO European region was declared polio free. Since the virus is still present in other parts of the world, importation of cases remains possible and travellers to endemic areas should be adequately counselled.

Read more about polio in the factsheet for general public and factsheet for health professionals