Polio Frequently Asked Questions
What is polio?
Polio, or poliomyelitis, is an acute illness brought on when one of three types of polio virus (types 1, 2, or 3) invades the gastro-intestinal tract. In September 2015 the Global Commission for the Certification of Poliomyelitis Eradication (GCC) declared type 2 wild poliovirus (WPV2) officially eradicated, as no cases of this serotype had been detected globally since October 1999.
Polio is a highly infectious viral disease. The virus has an affinity for nervous tissue, and can cause paralysis if it reaches the central nervous system. Many infected people have no symptoms, but do excrete the virus in their faeces, hence transmitting infection to others.
What are the symptoms of polio?
Initial symptoms are fever, fatigue, headache, vomiting, stiffness in the neck and pain in the limbs. Clinically inapparent infection is common. One in 200 infections leads to irreversible paralysis (usually in the legs). Among those paralysed, 5%–10% die when their breathing muscles become immobilised.
How is polio spread?
Poliovirus is mainly passed through person-to-person contact. The virus enters the environment through faeces of people infected then is passed to others especially in situations of poor hygiene. The disease may infect thousands of people, depending on the level of sanitation, before the first case of polio paralysis emerges. Individuals can carry the virus in their intestines just long enough to transmit to others.
What is the incubation period of polio?
Its incubation period is 3-21 days.
Who is most at risk of polio?
Polio mainly affects children under five years of age. However, immune and or partially immune adults and children can still be infected with poliovirus and carry the virus for long enough to take the virus from one country to another, infecting close contacts.
How can polio be prevented?
There is no cure for polio, it can only be prevented through immunisation. Routine immunisation was introduced in Ireland in 1957, but people born before then may not have been immunised.
Vaccination against polio
Poliovirus infection provides lifelong immunity against the disease, but this protection is limited to the particular type of poliovirus involved (Type 1, 2, or 3). Two different kinds of vaccine have been used until recent changes recommended by WHO:
- A live attenuated (weakened) oral polio vaccine (OPV) developed by Dr. Albert Sabin in 1961. OPV is given orally.
- An inactivated (killed) polio vaccine (IPV), developed in 1955 by Dr. Jonas Salk; unlike OPV, IPV has to be injected.
Both vaccines have been highly effective against all three types of poliovirus. There are however, significant differences in the way each vaccine works.
Withdrawal of trivalent oral polio vaccine in the European Region (OPV switch)
All oral polio vaccines (OPV) are made from live attenuated (weakened) polioviruses. Due to natural evolution in one (or several) human beings, these viruses can in very rare cases mutate into vaccine-derived poliovirus (VDPV) and acquire the capacity for long-term circulation that can even lead to polio outbreaks, especially in areas of low vaccination coverage.
As planned in the Polio Eradication and Endgame Strategic Plan 2013–2018, gradual withdrawal of the type 2 component (OPV2) began in 2016. The choice to withdraw OPV2 was based on the fact that Wild poliovirus type 2 was no longer circulating anywhere in the world. And that OPV2 interferes with the immune response to poliovirus types 1 and 3; therefore its withdrawal from the vaccine increases the effectiveness of immunisation against polioviruses of other serotypes.
All immunisation programmes in the world that use OPV were required to switch from trivalent OPV (containing all 3 poliovirus types) to bivalent OPV (containing only types 1 and 3), or move to an inactivated polio vaccine (IPV)-only schedule, in a globally synchronised manner between 17 April and 1 May 2016. In addition, at least one dose of IPV is being added to the routine immunisation schedule in each country that uses bivalent OPV to boost protection against all three types of poliovirus.
Further information on the switch to bivalent OPV or IPV in the European region is located on the WHO-EURO website
What polio vaccine is used in Ireland?
Inactivated polio vaccine (IPV) is the vaccine currently used routinely in Ireland. IPV vaccine replaced routine use of OPV vaccine in 2001.
- Polio vaccines are given as part of the routine childhood schedule at 2,4,6 months of age and a booster is given at 4-5 years of age
- Unimmunised older children and adults are recommended three doses of polio vaccine
- Partially immunised adults should complete the course
Fully vaccinated adults at increased risk of exposure to world polio virus should be given a dose of IPV:
- Those travelling to areas of the world where polio is common
- Those in contact with specimens that may contain wild poliovirus
- Those in contact with patients who may be excreting wild poliovirus
All travellers to countries where polio is circulating should be up-to-date with their polio vaccinations before travel.
Polio in Ireland (historic)
Before the introduction of polio vaccine in 1957 polio used to be common in Ireland. By the mid-1960s few cases were reported. The last case of polio was reported in 1984. See the HPSC website for details.
Acute Flaccid Paralysis (AFP) surveillance
Acute flaccid or floppy paralysis is defined as any case of new onset of hypotonic weakness in a child aged less than 15 years of age. This includes possible illness due to Guillian-Barré syndrome, transverse myelitis, traumatic neuritis, viral infections caused by other enteroviruses, toxins and tumours. Isolated facial paralysis is not included. In the early stages of the disease polio may be difficult to differentiate from other forms of AFP. Therefore, to insure that no case of polio goes undetected surveillance targets a symptom (AFP) rather than a specific disease (e.g. polio).
Last reviewed: 25 June 2019