Polio is an infectious disease caused by a virus. It can affect the nervous system, causing very serious consequences including paralysis or death.
Before a vaccine was introduced in the 1950s, epidemics of polio would result in up to 7760 cases of paralytic polio in the UK each year, with up to 750 deaths. Since 1984, there have been no cases of polio contracted naturally in the UK, and vaccination has eradicated the disease from Europe, and almost all other countries as well. Polio is now endemic in just two countries: Afghanistan and Pakistan.
They include fever, headache, upset stomach, stiffness of the neck and back, and paralysis. Polio can also lead to meningitis. (See the Meningitis Research Foundation website for more detailed information on the signs and symptoms of meningitis.)
Polio is caused by infection with one of three types of virus. The virus is passed on from person to person through contact with faeces, saliva or mucus. Infection does not always cause symptoms, so it is possible to carry and pass on the disease without being aware of having it.
Until 2004, the routine vaccine against polio was a live, oral polio vaccine (OPV). In a small number of cases this vaccine actually caused polio itself (30 cases in UK between 1985 and 2002). Although the disease had been eradicated in the UK, it remained endemic in many countries, so there was a risk it could be reintroduced to the UK through travel and immigration.
By 2004, vaccination had eradicated polio from all but a few countries worldwide, and the UK was able to switch over to the inactivated polio vaccine, which cannot cause the disease itself.