Immunization, Vaccines and Biologicals


Polio (poliomyelitis) is a highly infectious viral disease. The poliovirus invades the nervous system and can cause irreversible paralysis in a matter of hours. Polio is spread through person-to-person contact. When a child is infected with wild poliovirus, the virus enters the body through the mouth and multiplies in the intestine. It is then shed into the environment through the faeces where it can spread rapidly through a community, especially in situations of poor hygiene and sanitation. If a sufficient number of children are fully immunized against polio, the virus is unable to find susceptible children to infect, and dies out.

Most infected people (90%) have no symptoms or very mild symptoms and usually go unrecognized. In others, initial symptoms include fever, fatigue, headache, vomiting, stiffness in the neck and pain in the limbs.

There is no cure for polio, only treatment to alleviate the symptoms. Heat and physical therapy is used to stimulate the muscles and antispasmodic drugs are given to relax the muscles. While this can improve mobility, it cannot reverse permanent polio paralysis.

There are 3 types of wild poliovirus (WPV) - types 1, 2 and 3. In September 2015, WPV type 2 was officially declared eradicated. Since WPV type 3 has not been detected since November 2012, WPV type 1 is probably the only wild poliovirus type that remains in circulation.

Polio can be prevented through immunization. Polio vaccine, given multiple times, almost always protects a child for life. The development of effective vaccines to prevent paralytic polio was one of the major medical breakthroughs of the 20th century. There are six different vaccines to stop polio transmission:

  • Inactivated polio vaccine (IPV) – protects against poliovirus types 1, 2, and 3
  • Trivalent oral polio vaccine (tOPV) – protects against poliovirus types 1, 2, and 3 - following the "OPV Switch" in April 2016, tOPV is no longer in use
  • Bivalent oral polio vaccine (bOPV) – protects against poliovirus types 1, and 3
  • Monovalent oral polio vaccines (mOPV1, mOPV2 and mOPV3) – protect against each individual type of poliovirus, respectively

If enough people in a community are immunized, the virus will be deprived of susceptible hosts and will die out. High levels of vaccination coverage must be maintained to stop transmission and prevent outbreaks occurring.

The Polio Eradication and Endgame Strategy

In May 2012, the World Health Assembly declared the completion of polio eradication a programmatic emergency for global public health and the Polio Eradication and Endgame Strategic Plan 2013-2018 was developed and, in November 2012, endorsed by SAGE. Under objective 2 of the Eradication and Endgame Plan, at least one dose of inactivated poliomyelitis vaccine (IPV) should be introduced into all routine immunization programmes globally, and trivalent oral polio vaccines (tOPV) will be replaced with bivalent (bOPV) in all OPV-using countries. The global "OPV Switch" was successfully conducted worldwide in April 2016 – setting the stage for the eventual withdrawal of all OPV.

See more at: IPV Introduction, OPV Withdrawal and Routine Immunization Strengthening

In the new Eradication and Endgame strategy, research is a vital component of the Global Polio Eradication Initiative, providing the necessary evidence to guide the final steps to a lasting polio-free world and beyond. The Global Polio Eradication Initiative coordinates and supports an extensive program of research from a wide range of core scientific disciplines. The research program has two broad objectives:

  • to identify, develop and evaluate new tools and tailored approaches to maximize the impact of eradication efforts
  • to inform long-term policy for the post-eradication era.

See more at: Polio eradication research

WHO position papers

Disease burden and surveillance

Vaccine topics

SAGE recommendations for polio

Further information

Page last updated: 9 February 2017