April 12, 2018

Poliomyelitis - Symptoms, Transmission, Prevention and Key Facts

Polio, or poliomyelitis or infantile paralysis, is a crippling and potentially deadly infectious disease. It is caused by the poliovirus. The virus spreads from person to person and can invade an infected person’s brain and spinal cord, causing paralysis (inability to move parts of the body).

Polio and its symptoms

Polio is a highly infectious disease caused by a virus. It invades the nervous system, and can cause total paralysis in a matter of hours.

Most people who get infected with poliovirus (about 72 out of 100) will not have any visible symptoms. About 1 out of 4 people with poliovirus infection will have flu-like symptoms. Initial symptoms are fever, sore throat, fatigue, headache, nausea, vomiting, and stomach pain. These symptoms usually last 2 to 5 days then go away on their own.

A smaller proportion of people with poliovirus infection will develop other more serious symptoms that affect the brain and spinal cord:
  • Paresthesia (feeling of pins and needles in the legs)
  • Meningitis (infection of the covering of the spinal cord and/or brain) occurs in about 1 out of 25 people with poliovirus infection causing stiffness of the neck
  • Paralysis (inability to move parts of the body) or weakness in the arms, legs, or both, occurs in about 1 out of 200 people with poliovirus infection
Paralysis is the most severe symptom associated with polio because it can lead to permanent disability and death. Between 5 and 10 out of 100 people who have paralysis from poliovirus infection die because the virus affects the muscles that help them breathe.

Even children who seem to fully recover can develop new muscle pain, weakness, or paralysis as adults, 15 to 40 years later. This is called post-polio syndrome.

Note that “poliomyelitis” (or “polio” for short) is defined as the paralytic disease. So only people with the paralytic infection are considered to have the disease.


Poliovirus only infects humans. It is very contagious and is transmitted by person-to-person spread mainly through the faecal-oral route or, less frequently, by a common vehicle (for example, contaminated water or food) and multiplies in the intestine.

The virus lives in an infected person’s throat and intestines. It enters the body through the mouth and spreads through contact with the faeces (poop) of an infected person and, though less common, through droplets from a sneeze or cough. You can get infected with poliovirus if you have faeces on your hands and you touch your mouth. Also, you can get infected if you put in your mouth objects like toys that are contaminated with faeces (poop).

An infected person may spread the virus to others immediately before and about 1 to 2 weeks after symptoms appear. The virus can live in an infected person’s faeces for many weeks. It can contaminate food and water in unsanitary conditions.

People who don’t have symptoms can still pass the virus to others and make them sick.

People most at risk
Polio mainly affects children under 5 years of age.


There is no cure for polio, it can only be prevented. Polio vaccine, given multiple times, can protect a child for life.

There are two types of vaccine that can prevent polio: inactivated poliovirus vaccine (IPV) and oral poliovirus vaccine (OPV). Only IPV has been used in the United States since 2000; OPV is used throughout much of the world.

Global caseload

Wild poliovirus cases have decreased by over 99% since 1988, from an estimated 350 000 cases in more than 125 endemic countries then, to 22 reported cases in 2017.

Of the 3 strains of wild poliovirus (type 1, type 2, and type 3), wild poliovirus type 2 was eradicated in 1999 and no case of wild poliovirus type 3 has been found since the last reported case in Nigeria in November 2012.

Key facts

To summarize, the following are true:
  • Polio (poliomyelitis or infantile paralysis) mainly affects children under 5 years of age.
  • 1 in 200 infections leads to irreversible paralysis. Among those paralysed, 5% to 10% die when their breathing muscles become immobilized.
  • Cases due to wild poliovirus have decreased by over 99% since 1988, from an estimated 350 000 cases then, to 22 reported cases in 2017. As a result of the global effort to eradicate the disease, more than 16 million people have been saved from paralysis.
  • As long as a single child remains infected, children in all countries are at risk of contracting polio. Failure to eradicate polio from these last remaining strongholds could result in as many as 200 000 new cases every year, within 10 years, all over the world.
  • In most countries, the global effort has expanded capacities to tackle other infectious diseases by building effective surveillance and immunization systems.

WHO Response

Launch of the Global Polio Eradication Initiative

In 1988, the Forty-first World Health Assembly adopted a resolution for the worldwide eradication of polio. It marked the launch of the Global Polio Eradication Initiative (GPEI), spearheaded by national governments, WHO, Rotary International, the US Centers for Disease Control and Prevention (CDC), UNICEF, and supported by key partners including the Bill & Melinda Gates Foundation. This followed the certification of the eradication of smallpox in 1980, progress during the 1980s towards elimination of the poliovirus in the Americas, and Rotary International’s commitment to raise funds to protect all children from the disease.


Overall, since the GPEI was launched, the number of cases has fallen by over 99%.

In 1994, the WHO Region of the Americas was certified polio-free, followed by the WHO Western Pacific Region in 2000 and the WHO European Region in June 2002. On 27 March 2014, the WHO South-East Asia Region was certified polio-free, meaning that transmission of wild poliovirus has been interrupted in this bloc of 11 countries stretching from Indonesia to India. This achievement marks a significant leap forward in global eradication, with 80% of the world’s population now living in certified polio-free regions.

More than 16 million people are able to walk today, who would otherwise have been paralysed. An estimated 1.5 million childhood deaths have been prevented, through the systematic administration of vitamin A during polio immunization activities.

Opportunity and risks: an emergency approach

The strategies for polio eradication work when they are fully implemented. This is clearly demonstrated by India’s success in stopping polio in January 2011, in arguably the most technically-challenging place, and polio-free certification of the entire South-East Asia Region of WHO occurred in March 2014.

Failure to implement strategic approaches, however, leads to ongoing transmission of the virus. Endemic transmission is continuing in Afghanistan, Nigeria and Pakistan. Failure to stop polio in these last remaining areas could result in as many as 200 000 new cases every year, within 10 years, all over the world.

Recognizing both the epidemiological opportunity and the significant risks of potential failure, the "Polio Eradication and Endgame Strategic Plan" was developed, in consultation with polio-affected countries, stakeholders, donors, partners and national and international advisory bodies. The new Plan was presented at a Global Vaccine Summit in Abu Dhabi, United Arab Emirates, at the end of April 2013. It is the first plan to eradicate all types of polio disease simultaneously – both due to wild poliovirus and due to vaccine-derived polioviruses.

Future benefits of polio eradication

Once polio is eradicated, the world can celebrate the delivery of a major global public good that will benefit all people equally, no matter where they live. Economic modelling has found that the eradication of polio would save at least US$ 40–50 billion, mostly in low-income countries. Most importantly, success will mean that no child will ever again suffer the terrible effects of lifelong polio-paralysis.

1). World Health Organization: Poliomyelitis - WHO Fact Sheets. Accessed 11.04.18. Available here: http://www.who.int/mediacentre/factsheets/fs114/en/
2). Centers for Disease Control: Polio - Global Health. Accessed 12.04.18. Available here: https://www.cdc.gov/polio/
3). NHS Choices: Polio. Accessed 12.04.18. Available here: https://www.nhs.uk/conditions/polio/
4). Wikipedia, the Free Encyclopedia: Poliomyelitis. Accessed 11.04.18. Available here: https://en.wikipedia.org/wiki/Poliomyelitis

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