Poliomyelitis (polio) is caused by polioviruses, classified into types 1, 2 and 3. Humans are the only reservoir of the infection: the poliovirus is carried in the bowel and in the throat of infected individuals. Poliovirus is highly contagious and infected individuals shed virus in the faeces and from oral secretions, thus the mode of transmission is person-to-person, both via the faecal-oral and the oral-oral routes.
When the virus is ingested, it enters the bowel where it multiplies. The clinical manifestations of poliovirus infection vary greatly. The majority of infected persons (95%) do not have any clinical symptoms. Minor illness or abortive poliomyelitis is the most common form of clinical disease (4–8% of infections) and characterised by unspecific symptoms such as fever, headache, nausea, vomiting, abdominal pain and/or sore throat. After exposure and an incubation period of one-to-two weeks, the virus can spread from the digestive tract to the central nervous system, and cause meningitis or paralysis due to neural damage. Paralytic illness (poliomyelitis) is rare, affecting less than 1% of infected individuals.
No specific therapy is available against the virus. However, effective vaccines against polio are available, making vaccination essential to preventing the disease. There are two types of polio vaccines; an oral live attenuated (weakened) vaccine (oral polio vaccine; OPV) and an inactivated (killed) vaccine (inactivated polio vaccine; IPV). Both vaccines contain combinations of the three poliovirus types since all are needed to provide protection against the three poliovirus types.
Childhood immunisation programmes with OPV or IPV have been effective in stopping the transmission of poliovirus and eliminating the virus from many areas in the world. In the EU/EEA, all Member States offer a childhood vaccination schedule against polio using the IPV; the vaccine of choice in areas free of poliovirus or with very low levels.
The last case of endemic paralytic polio in the European Region (i.e. with the source of the infection originating in the region) was reported in Turkey in November 1998. In June 2002, the WHO European region was officially declared polio-free. Since the virus is still regularly present in other parts of the world, and has occurred in the WHO European region as recently as 2005 in Tajikistan and in 2013-2014 in Israel, importation of the infection as well as of polio cases remains possible. It is therefore essential to maintain a high level of vaccination in the EU/EEA (>90%) and ensure that EU/EEA travellers to areas where poliovirus is currently circulating (see www.polioeradication.org for a list of countries) are adequately vaccinated and counseled for the importance of hand washing and only drinking clean water.