Poliomyelitis, often called polio or infantile paralysis, is an infectious disease caused by the poliovirus. In about 0.5% of cases there is muscle weaknessresulting in an inability to move.[1] This can occur over a few hours to few days.[1][2] The weakness most often involves the legs but may less commonly involve the muscles of the head, neck and diaphragm. Many but not all people fully recover. In those with muscle weakness about 2% to 5% of children and 15% to 30% of adults die.[1] Another 25% of people have minor symptoms such as fever and a sore throat and up to 5% have headache, neck stiffness and pains in the arms and legs.[1][2] These people are usually back to normal within one or two weeks. In up to 70% of infections there are no symptoms.[1] Years after recovery post-polio syndrome may occur, with a slow development of muscle weakness similar to that which the person had during the initial infection.[3]

Poliovirus is usually spread from person to person through infected fecal matter entering the mouth.[1] It may also be spread by food or water containing human feces and less commonly from infected saliva.[1][2] Those who are infected may spread the disease for up to six weeks even if no symptoms are present. The disease may be diagnosed by finding the virus in the feces or detecting antibodies against it in the blood.[1]

The disease is preventable with the polio vaccine; however, a number of doses are required for it to be effective.[2] The United States Center for Disease Control recommends polio vaccination boosters for travelers and those who live in countries where the disease is occurring.[4] Once infected there is no specific treatment.[2] In 2013 polio affected 416 people down from 350,000 cases in 1988.[2] In 2014 the disease was only spreading between people inAfghanistanNigeria, and Pakistan.[2] In 2015 Nigeria had stopped the spread of wild poliovirus.[5]

Poliomyelitis has existed for thousands of years, with depictions of the disease in ancient art.[1] The disease was first recognized as a distinct condition byMichael Underwood in 1789[1] and the virus that causes it was first identified in 1908 by Karl Landsteiner.[6] Major outbreaks started to occur in the late 19th century in Europe and the United States.[1] In the 20th century it became one of the most worrying childhood diseases in these areas.[7] The first polio vaccine was developed in the 1950s by Jonas Salk.[8] It is hoped that vaccination efforts and early detection of cases will result in global eradication of the disease by 2018.[9] In 2013; however, there were reports of new cases in Syria[10] and in May 2014, the World Health Organization declared a public health emergency of international concern due to outbreaks of the disease in Asia, Africa and the Middle East.[11] The disease does not naturally occur in any other animals.[1]

Polio is caused by the poliovirus, a highly contagious virus specific to humans. The virus usually enters the environment in the feces of someone who is infected. In areas with poor sanitation, the virus easily spreads through the fecal-oral route, via contaminated water or food.
 Also called “trivalent oral polio vaccine” or “Sabin vaccine”, OPV consists of a mixture of live, attenuated (weakened) poliovirus strains of all three poliovirus types. The oral polio vaccine is simple to administer. A few drops, given multiple times, can protect a child for life.

Why does my baby need the polio vaccine?

The polio vaccine protects your child against polio or poliomyelitis, which is a highly infectious viral disease spread through the faeces of infected people. 

The polio virus enters through the mouth and ends up in the nervous system. It can rapidly lead to paralysis and even death. 

India has been declared a polio-free nation. However, it is still mandatory that all children under the age of five years continue to receive the polio vaccine. 

This is because polio still exists in certain other countries of the world. There is a risk of the virus getting imported into India. Hence, in view of this continuing risk, your child needs the polio vaccine

Polio mainly affects children under the age of five. Older people with lower immunity levels are also vulnerable. 

It is a common belief that polio afflicts only the lower socio-economic group. That is not true: as long as there is one infected person, all children are at risk. 

There is no cure for polio. The most effective way of preventing polio is by immunising your child with the polio vaccine at the right time. 

Older siblings who are under five years of age must also be vaccinated in case they have missed a dose.. 

Are there different forms of the polio vaccine?

There are two types of polio vaccines:

Oral polio vaccine (OPV)  
The OPV is a live but weakened form of the virus which makes the body produce antibodies against it without developing into the disease. Given as oral drops, it protects not only the person who has taken them but also others living around him. 


Once the live vaccine virus is introduced into the body, it spreads to others through the water supply, the sewage system or food and drinking water. This way an entire household, and sometimes whole communities, can get protected as the vaccine virus helps them develop antibodies against the disease. 

Inactivated polio vaccine (IPV)
The IPV, on the other hand, while highly effective, only protects the vaccinated person, and not others. It is given by injection. 


What are the symptoms of polio?

Symptoms of polio can range from mild to severe. They include:

  • headache
  • fever
  • sore throat
  • nausea
  • severe muscle pain
  • stiffness in the neck and back

As most of these symptoms are common to a viral flu, consult your doctor if your baby has any of them. In most cases, there are no symptoms. In just one per cent of the cases, the virus enters the nervous system and can cause paralysis. 

Can I give IPV to my baby when she has fever or diarrhoea?

If your child is ill at the time the IPV shot is scheduled, it is usually postponed until she recovers. The OPV, on the other hand, can be given even with fever or diarrhoea. If your baby is unwell, ask your doctor to be sure about what is best for your child. 

Check out our immunisation scheduler to find out when to give your baby the polio vaccine.


Oral polio vaccine (OPV)

The oral polio vaccine (OPV) was developed in 1961 by Albert Sabin. Also called “trivalent oral polio vaccine” or “Sabin vaccine”, OPV consists of a mixture of live, attenuated (weakened) poliovirus strains of all three poliovirus types.

Boy receiving oral polio vaccine, Kano, Nigeria
The oral polio vaccine is simple to administer. A few drops, given multiple times, can protect a child for life. 
WHO/Rod Curtis

OPV produces antibodies in the blood to all three types of poliovirus. In the event of infection, these antibodies protect against paralysis by preventing the spread of wild poliovirus to the nervous system. 

OPV also produces a local, mucosal immune response in the mucous membrane of the intestines. In the event of infection, these mucosal antibodies limit the replication of the wild poliovirus inside the intestine. This intestinal immune response to OPV is thought to be the main reason why mass campaigns with OPV can rapidly stop person-to-person transmission of wild poliovirus.


  • OPV is administered orally. It can be given by volunteers and does not require trained health workers or sterile injection equipment.
  • The vaccine is relatively inexpensive. In 2011, the cost of a single dose for public health programmes in developing countries was between 11 and 14 US cents. 
  • OPV is safe, effective, and induces long-lasting immunity to all three types of poliovirus.
  • For several weeks after vaccination, the vaccine virus replicates in the intestine, is excreted in the faeces, and can be spread to others in close contact. This means that in areas where hygiene and sanitation are poor, immunization with OPV can result in the “passive” immunization of people who have not been directly vaccinated.
  • Safety

    OPV is an extremely safe vaccine. All OPV used in supplementary immunization activities for the Global Polio Eradication Initiative is pre-qualified by WHO and procured through UNICEF. In 2006, WHO issued a statement to affirm the quality and safety of OPV.

    A vial of OPV
    Oral polio vaccine is usually provided in vials containing 10–20 doses of vaccine. A single dose is usually two drops



OPV is highly effective against all three types of wild poliovirus. When this vaccine is used however, there is competition among the three viruses to cause immunity, which results in protection but not with equal efficiency for each type: it is most effective against type 2.

One dose of OPV produces immunity to all three poliovirus serotypes in approximately 50% of recipients. Three doses produce immunity in more than 95% of recipients. Immunity is long-lasting and probably life-long.

Recommended use

In most countries, OPV remains the vaccine of choice in routine immunization schedules and supplementary immunization activities. 

Where more than one type of wild poliovirus is circulating, OPV is epidemiologically and operationally the best vaccine to use because protection develops to each of the three types of polio virus.


Poliomyelitis (polio) is a highly infectious viral disease, which mainly affects young children. The virus is transmitted by person-to-person spread mainly through the faecal-oral route or, less frequently, by a common vehicle (e.g. contaminated water or food) and multiplies in the intestine, from where it can invade the nervous system and can cause paralysis.

Initial symptoms of polio include fever, fatigue, headache, vomiting, stiffness in the neck, and pain in the limbs. In a small proportion of cases, the disease causes paralysis, which is often permanent. There is no cure for polio, it can only be prevented by immunization                                                  There are three types of polio infections:

  • Sub-clinical: Approximately 95 percent of polio cases are sub-clinical, and patients may not experience any symptoms. This form of polio does not affect the central nervous system (the brain and spinal cord).
  • Non-paralytic: This form, which does affect the central nervous system, produces only mild symptoms and does not result in paralysis.
  • Paralytic: This is the rarest and most serious form of polio, which produces full or partial paralysis in the patient. There are three types of paralytic polio: spinal polio (affects the spine), bulbar polio (affects the brainstem), and bulbospinal polio (affects the spine and brainstem).

Post-polio syndrome is a complication that can occur after a person has caught and recovered from poliovirus. Symptoms of the syndrome can appear up to 35 years after the polio infection.

What Causes Polio?

Poliovirus is often transmitted from person-to-person through fecal matter. People living in areas with limited access to running water or flush toilets often get the virus from drinking water contaminated by human waste that contains the virus.

In addition, the virus can be spread by contaminated food or water or direct contact with another infected person. According to the May Clinic, the virus that causes polio is so contagious that anyone living with an infected person will likely become infected themselves. 

Pregnant women, people with weakened immune systems, such as HIV+ people, and young children are the most susceptible to the polio virus. If you have not been vaccinated, you increase your risk of contracting polio by:

  • traveling to an area that has had a recent polio outbreak
  • taking care of or living with someone infected with polio
  • handling a laboratory specimen of the virus
  • having your tonsils removed
  • extreme stress, which can compromise immune system functio

Sub-Clinical Polio

  • If patients do have symptoms, they usually last for 72 hours or less and may include:

    • headache
    • sore, red throat
    • slight fever
    • vomiting
    • general discomfort

Non-Paralytic Polio

  • The symptoms of non paralytic polio may last for a couple of days to a week or two and includes

    • fever
    • sore throat in the absence of upper respiratory infection
    • headache
    • vomiting
    • fatigue
    • abnormal reflexes
    • problems swallowing and/or breathing
    • back and neck pain and stiffness, particularly neck stiffness with forward flexion of the neck
    • arm and leg pain or stiffness
    • muscle tenderness and spasms

      Paralytic Polio

  • People with paralytic polio experience the symptoms associated with non-paralytic polio first. Soon after, the following symptoms appear:

    • loss of reflexes
    • severe spasms and muscle pain
    • loose and floppy limbs, sometimes on just one side of the body, this is due to the weakness which results from the involvement of the spine
    • sudden paralysis (temporary or permanent)
    • deformed limbs (especially the hips, ankles, and feet due to prolonged weakenss and the lack of appropriate orthopedic bracing

    Full paralysis can eventually develop, but it is rare. Only about one percent of all polio cases will result in a person being permanently paralyzed. Of those patients who experience paralysis, five to 10 percent will die when the paralysis attacks the muscles that control breathing. (CDC)

           Post-Polio Syndrome

  •    The symptoms of post-polio syndrome are:

    • continuing muscle and joint weakness
    • muscle pain that gets worse
    • becoming easily exhausted or fatigued
    • muscle wasting, also called muscle atrophy
    • trouble breathing and/or swallowing
    • sleep related breathing problems (sleep apnea)
    • becoming easily cold or
    • new onset of weakness in previously uninvolved muscles

How Do Doctors Diagnose Polio?

    • Doctors will use the patient’s reported symptoms to help determine whether he or she has polio. During a physical examination, a doctor may notice that the patient has impaired reflexes, back and neck stiffness, or difficulty lifting his or her head while lying flat.

      To definitively diagnose polio, a doctor will take a sample of the patient’s throat secretions, stool, or cerebrospinal fluid (fluid surrounding the brain and spinal cord). The sample is then tested to see if it contains poliovirus and if the cells in the cerebrospinal fluid demonstrate changes consistent with what is called aseptic meningitis (a brain infection)


      Signs and symptoms

      Outcomes of poliovirus infection
      OutcomeProportion of cases[1]
      No symptoms72%
      Minor illness24%
      Nonparalytic aseptic
      Paralytic poliomyelitis0.1–0.5%
      — Spinal polio79% of paralytic cases
      — Bulbospinal polio19% of paralytic cases
      — Bulbar polio2% of paralytic cases

      The term “poliomyelitis” is used to identify the disease caused by any of the three serotypes of poliovirus. Two basic patterns of polio infection are described: a minor illness which does not involve the central nervous system (CNS), sometimes called abortive poliomyelitis, and a major illness involving the CNS, which may be paralytic or nonparalytic.[12] In most people with a normal immune system, a poliovirus infection is asymptomatic. Rarely, the infection produces minor symptoms; these may include upper respiratory tract infection (sore throat and fever), gastrointestinal disturbances (nausea, vomiting, abdominal pain, constipation or, rarely, diarrhea), and influenza-like illness.[1]

      The virus enters the central nervous system in about 1% of infections. Most patients with CNS involvement develop nonparalytic aseptic meningitis, with symptoms of headache, neck, back, abdominal and extremity pain, fever, vomiting, lethargy, and irritability.[13][14] About one to five in 1000 cases progress toparalytic disease, in which the muscles become weak, floppy and poorly controlled, and, finally, completely paralyzed; this condition is known as acute flaccid paralysis.[15] Depending on the site of paralysis, paralytic poliomyelitis is classified as spinal, bulbar, or bulbospinal. Encephalitis, an infection of the brain tissue itself, can occur in rare cases, and is usually restricted to infants. It is characterized by confusion, changes in mental status, headaches, fever, and, less commonly, seizures and spastic paralysis.[16]


      TEM micrograph of poliovirus

      Poliomyelitis is caused by infection with a member of the genus Enterovirus known as poliovirus (PV). This group of RNA viruses colonize the gastrointestinal tract[17] — specifically the oropharynx and the intestine. The incubation time (to the first signs and symptoms) ranges from three to 35 days, with a more common span of six to 20 days.[1] PV infects and causes disease in humans alone.[18] Its structure is very simple, composed of a single (+) sense RNA genome enclosed in a protein shell called a capsid.[18] In addition to protecting the virus’s genetic material, the capsid proteins enable poliovirus to infect certain types of cells. Threeserotypes of poliovirus have been identified—poliovirus type 1 (PV1), type 2 (PV2), and type 3 (PV3)—each with a slightly different capsid protein.[19] All three are extremely virulent and produce the same disease symptoms.[18] PV1 is the most commonly encountered form, and the one most closely associated with paralysis.[20]

      Individuals who are exposed to the virus, either through infection or by immunization with polio vaccine, develop immunity. In immune individuals, IgA antibodiesagainst poliovirus are present in the tonsils and gastrointestinal tract, and are able to block virus replication; IgG and IgM antibodies against PV can prevent the spread of the virus to motor neurons of the central nervous system.[21] Infection or vaccination with one serotype of poliovirus does not provide immunity against the other serotypes, and full immunity requires exposure to each serotype.[21]

      A rare condition with a similar presentation, nonpoliovirus poliomyelitis, may result from infections with nonpoliovirus enteroviruses.[22]


      Poliomyelitis is highly contagious via the fecal-oral (intestinal source) and the oral-oral (oropharyngeal source) routes.[21] In endemic areas, wild polioviruses can infect virtually the entire human population.[23] It is seasonal in temperate climates, with peak transmission occurring in summer and autumn.[21] These seasonal differences are far less pronounced in tropical areas.[23] The time between first exposure and first symptoms, known as the incubation period, is usually 6 to 20 days, with a maximum range of three to 35 days.[24] Virus particles are excreted in the feces for several weeks following initial infection.[24] The disease is transmitted primarily via the fecal-oral route, by ingesting contaminated food or water. It is occasionally transmitted via the oral-oral route,[20] a mode especially visible in areas with good sanitation and hygiene.[21] Polio is most infectious between seven and 10 days before and after the appearance of symptoms, but transmission is possible as long as the virus remains in the saliva or feces.[20]

      Factors that increase the risk of polio infection or affect the severity of the disease include immune deficiency,[25] malnutrition,[26] physical activity immediately following the onset of paralysis,[27]skeletal muscle injury due to injection of vaccines or therapeutic agents,[28] and pregnancy.[29] Although the virus can cross the maternal-fetal barrier during pregnancy, the fetus does not appear to be affected by either maternal infection or polio vaccination.[30] Maternal antibodies also cross the placenta, providing passive immunity that protects the infant from polio infection during the first few months of life.[31]

      As a precaution against infection, public swimming pools were often closed in affected areas during poliomyelitis epidemics.


      A blockage of the lumbar anterior spinal cord artery due to polio (PV3)

      Poliovirus enters the body through the mouth, infecting the first cells with which it comes in contact — the pharynx and intestinal mucosa. It gains entry by binding to an immunoglobulin-like receptor, known as the poliovirus receptor or CD155, on the cell membrane.[32] The virus then hijacks the host cell’s own machinery, and begins to replicate. Poliovirus divides within gastrointestinal cells for about a week, from where it spreads to the tonsils (specifically the follicular dendritic cellsresiding within the tonsilar germinal centers), the intestinal lymphoid tissue including the M cells of Peyer’s patches, and the deep cervical and mesenteric lymph nodes, where it multiplies abundantly. The virus is subsequently absorbed into the bloodstream.[33]

      Known as viremia, the presence of virus in the bloodstream enables it to be widely distributed throughout the body. Poliovirus can survive and multiply within the blood and lymphatics for long periods of time, sometimes as long as 17 weeks.[34] In a small percentage of cases, it can spread and replicate in other sites, such asbrown fat, the reticuloendothelial tissues, and muscle.[35] This sustained replication causes a major viremia, and leads to the development of minor influenza-like symptoms. Rarely, this may progress and the virus may invade the central nervous system, provoking a local inflammatory response. In most cases, this causes a self-limiting inflammation of the meninges, the layers of tissue surrounding the brain, which is known as nonparalytic aseptic meningitis.[13] Penetration of the CNS provides no known benefit to the virus, and is quite possibly an incidental deviation of a normal gastrointestinal infection.[36] The mechanisms by which poliovirus spreads to the CNS are poorly understood, but it appears to be primarily a chance event—largely independent of the age, gender, or socioeconomic position of the individual.[36]

      Paralytic polio

      Denervation of skeletal muscle tissue secondary to poliovirus infection can lead to paralysis.

      In around 1% of infections, poliovirus spreads along certain nerve fiber pathways, preferentially replicating in and destroying motor neurons within the spinal cord,brain stem, or motor cortex. This leads to the development of paralytic poliomyelitis, the various forms of which (spinal, bulbar, and bulbospinal) vary only with the amount of neuronal damage and inflammation that occurs, and the region of the CNS affected.

      The destruction of neuronal cells produces lesions within the spinal ganglia; these may also occur in the reticular formationvestibular nucleicerebellar vermis, and deep cerebellar nuclei.[36] Inflammation associated with nerve cell destruction often alters the color and appearance of the gray matter in the spinal column, causing it to appear reddish and swollen.[13] Other destructive changes associated with paralytic disease occur in the forebrain region, specifically the hypothalamus andthalamus.[36] The molecular mechanisms by which poliovirus causes paralytic disease are poorly understood.

      Early symptoms of paralytic polio include high fever, headache, stiffness in the back and neck, asymmetrical weakness of various muscles, sensitivity to touch,difficulty swallowingmuscle pain, loss of superficial and deep reflexesparesthesia (pins and needles), irritability, constipation, or difficulty urinating. Paralysis generally develops one to ten days after early symptoms begin, progresses for two to three days, and is usually complete by the time the fever breaks.[37]

      The likelihood of developing paralytic polio increases with age, as does the extent of paralysis. In children, nonparalytic meningitis is the most likely consequence of CNS involvement, and paralysis occurs in only one in 1000 cases. In adults, paralysis occurs in one in 75 cases.[38] In children under five years of age, paralysis of one leg is most common; in adults, extensive paralysis of the chest and abdomen also affecting all four limbs—quadriplegia—is more likely.[39] Paralysis rates also vary depending on the serotype of the infecting poliovirus; the highest rates of paralysis (one in 200) are associated with poliovirus type 1, the lowest rates (one in 2,000) are associated with type 2.[40]

      Spinal polio

      The location of motor neurons in theanterior horn cells of the spinal column

      Spinal polio, the most common form of paralytic poliomyelitis, results from viral invasion of the motor neurons of the anterior horn cells, or the ventral (front) grey matter section in the spinal column, which are responsible for movement of the muscles, including those of the trunklimbs, and the intercostal muscles.[15] Virus invasion causes inflammation of the nerve cells, leading to damage or destruction of motor neuron ganglia. When spinal neurons die, Wallerian degeneration takes place, leading to weakness of those muscles formerly innervated by the now-dead neurons.[41] With the destruction of nerve cells, the muscles no longer receive signals from the brain or spinal cord; without nerve stimulation, the muscles atrophy, becoming weak, floppy and poorly controlled, and finally completely paralyzed.[15] Maximum paralysis progresses rapidly (two to four days), and usually involves fever and muscle pain. Deep tendon reflexes are also affected, and are typically absent or diminished; sensation (the ability to feel) in the paralyzed limbs, however, is not affected.[42]

      The extent of spinal paralysis depends on the region of the cord affected, which may be cervicalthoracic, or lumbar.[43] The virus may affect muscles on both sides of the body, but more often the paralysis is asymmetrical.[33] Any limb or combination of limbs may be affected—one leg, one arm, or both legs and both arms. Paralysis is often more severe proximally (where the limb joins the body) than distally (the fingertips and toes).[33]

      Bulbar polio

      The location and anatomy of the bulbar region (in orange)

      Making up about 2% of cases of paralytic polio, bulbar polio occurs when poliovirus invades and destroys nerves within the bulbar region of the brain stem.[1] The bulbar region is a white matter pathway that connects the cerebral cortex to the brain stem. The destruction of these nerves weakens the muscles supplied by thecranial nerves, producing symptoms of encephalitis, and causes difficulty breathing, speaking and swallowing.[14] Critical nerves affected are the glossopharyngeal nerve (which partially controls swallowing and functions in the throat, tongue movement, and taste), the vagus nerve (which sends signals to the heart, intestines, and lungs), and the accessory nerve (which controls upper neck movement). Due to the effect on swallowing, secretions of mucus may build up in the airway, causing suffocation.[37] Other signs and symptoms include facial weakness (caused by destruction of the trigeminal nerve and facial nerve, which innervate the cheeks, tear ducts, gums, and muscles of the face, among other structures), double vision, difficulty in chewing, and abnormal respiratory rate, depth, and rhythm (which may lead to respiratory arrest). Pulmonary edema and shock are also possible and may be fatal.[43]

      Bulbospinal polio

      Approximately 19% of all paralytic polio cases have both bulbar and spinal symptoms; this subtype is called respiratory or bulbospinal polio.[1] Here, the virus affects the upper part of the cervical spinal cord (cervical vertebrae C3 through C5), and paralysis of the diaphragm occurs. The critical nerves affected are thephrenic nerve (which drives the diaphragm to inflate the lungs) and those that drive the muscles needed for swallowing. By destroying these nerves, this form of polio affects breathing, making it difficult or impossible for the patient to breathe without the support of a ventilator. It can lead to paralysis of the arms and legs and may also affect swallowing and heart functions.[44]


      Paralytic poliomyelitis may be clinically suspected in individuals experiencing acute onset of flaccid paralysis in one or more limbs with decreased or absent tendon reflexes in the affected limbs that cannot be attributed to another apparent cause, and without sensory or cognitive loss.[45]

      A laboratory diagnosis is usually made based on recovery of poliovirus from a stool sample or a swab of the pharynxAntibodies to poliovirus can be diagnostic, and are generally detected in the blood of infected patients early in the course of infection.[1] Analysis of the patient’s cerebrospinal fluid (CSF), which is collected by a lumbar puncture (“spinal tap”), reveals an increased number of white blood cells (primarily lymphocytes) and a mildly elevated protein level. Detection of virus in the CSF is diagnostic of paralytic polio, but rarely occurs.[1]

      If poliovirus is isolated from a patient experiencing acute flaccid paralysis, it is further tested through oligonucleotide mapping (genetic fingerprinting), or more recently by PCR amplification, to determine whether it is “wild type” (that is, the virus encountered in nature) or “vaccine type” (derived from a strain of poliovirus used to produce polio vaccine).[46] It is important to determine the source of the virus because for each reported case of paralytic polio caused by wild poliovirus, an estimated 200 to 3,000 other contagious asymptomatic carriers exist.[47]


Passive immunization

In 1950, William Hammon at the University of Pittsburgh purified the gamma globulin component of the blood plasma of polio survivors.[48] Hammon proposed the gamma globulin, which contained antibodies to poliovirus, could be used to halt poliovirus infection, prevent disease, and reduce the severity of disease in other patients who had contracted polio. The results of a large clinical trial were promising; the gamma globulin was shown to be about 80% effective in preventing the development of paralytic poliomyelitis.[49] It was also shown to reduce the severity of the disease in patients who developed polio.[48] Due to the limited supply of blood plasma gamma globulin was later deemed impractical for widespread use and the medical community focused on the development of a polio vaccine.[50]


A child receiving an oral polio vaccine

Two types of vaccine are used throughout the world to combat polio. Both types induce immunity to polio, efficiently blocking person-to-person transmission of wild poliovirus, thereby protecting both individual vaccine recipients and the wider community (so-called herd immunity).[51]

The first candidate polio vaccine, based on one serotype of a live but attenuated (weakened) virus, was developed by the virologist Hilary Koprowski. Koprowski’s prototype vaccine was given to an eight-year-old boy on 27 February 1950.[52] Koprowski continued to work on the vaccine throughout the 1950s, leading to large-scale trials in the then Belgian Congo and the vaccination of seven million children in Poland against serotypes PV1 and PV3 between 1958 and 1960.[53]

The second inactivated virus vaccine was developed in 1952 by Jonas Salk at the University of Pittsburgh, and announced to the world on 12 April 1955.[54] The Salk vaccine, or inactivated poliovirus vaccine (IPV), is based on poliovirus grown in a type of monkey kidney tissue culture (vero cell line), which is chemically inactivated with formalin.[21] After two doses of IPV (given by injection), 90% or more of individuals develop protective antibody to all three serotypes of poliovirus, and at least 99% are immune to poliovirus following three doses.[1]

Subsequently, Albert Sabin developed another live, oral polio vaccine (OPV). It was produced by the repeated passage of the virus through nonhuman cells at subphysiological temperatures.[55] The attenuated poliovirus in the Sabin vaccine replicates very efficiently in the gut, the primary site of wild poliovirus infection and replication, but the vaccine strain is unable to replicate efficiently within nervous system tissue.[56] A single dose of Sabin’s oral polio vaccine produces immunity to all three poliovirus serotypes in about 50% of recipients. Three doses of live-attenuated OPV produce protective antibody to all three poliovirus types in more than 95% of recipients.[1] Human trials of Sabin’s vaccine began in 1957,[57] and in 1958 it was selected, in competition with the live vaccines of Koprowski and other researchers, by the US National Institutes of Health.[53] Licensed in 1962,[57] it rapidly became the only polio vaccine used worldwide.[53]

Because OPV is inexpensive, easy to administer, and produces excellent immunity in the intestine (which helps prevent infection with wild virus in areas where it is endemic), it has been the vaccine of choice for controlling poliomyelitis in many countries.[58] On very rare occasions (about one case per 750,000 vaccine recipients), the attenuated virus in OPV reverts into a form that can paralyze.[24]Most industrialized countries have switched to IPV, which cannot revert, either as the sole vaccine against poliomyelitis or in combination with oral polio vaccine.[59]


There is no cure for polio. The focus of modern treatment has been on providing relief of symptoms, speeding recovery and preventing complications. Supportive measures include antibiotics to prevent infections in weakened muscles, analgesics for pain, moderate exercise and a nutritious diet.[60] Treatment of polio often requires long-term rehabilitation, including occupational therapyphysical therapy, braces, corrective shoes and, in some cases, orthopedic surgery.[43]

Portable ventilators may be required to support breathing. Historically, a noninvasive, negative-pressure ventilator, more commonly called an iron lung, was used to artificially maintain respiration during an acute polio infection until a person could breathe independently (generally about one to two weeks). Today, many polio survivors with permanent respiratory paralysis use modern jacket-type negative-pressure ventilators worn over the chest and abdomen.[61]

Other historical treatments for polio include hydrotherapyelectrotherapy, massage and passive motion exercises, and surgical treatments, such as tendon lengthening and nerve grafting.[15]


A child with a deformity of her right leg due to polio

Patients with abortive polio infections recover completely. In those who develop only aseptic meningitis, the symptoms can be expected to persist for two to ten days, followed by complete recovery.[62] In cases of spinal polio, if the affected nerve cells are completely destroyed, paralysis will be permanent; cells that are not destroyed, but lose function temporarily, may recover within four to six weeks after onset.[62] Half the patients with spinal polio recover fully; one-quarter recover with mild disability, and the remaining quarter are left with severe disability.[63] The degree of both acute paralysis and residual paralysis is likely to be proportional to the degree of viremia, and inversely proportional to the degree of immunity.[36] Spinal polio is rarely fatal.[37]

Without respiratory support, consequences of poliomyelitis with respiratory involvement include suffocation or pneumonia from aspiration of secretions.[61] Overall, 5–10% of patients with paralytic polio die due to the paralysis of muscles used for breathing. The case fatality rate (CFR) varies by age: 2–5% of children and up to 15–30% of adults die.[1] Bulbar polio often causes death if respiratory support is not provided;[44] with support, its CFR ranges from 25 to 75%, depending on the age of the patient.[1][64] When intermittent positive pressure ventilation is available, the fatalities can be reduced to 15%.[65]


Many cases of poliomyelitis result in only temporary paralysis.[15] Nerve impulses return to the formerly paralyzed muscle within a month, and recovery is usually complete in six to eight months.[62] The neurophysiological processes involved in recovery following acute paralytic poliomyelitis are quite effective; muscles are able to retain normal strength even if half the original motor neurons have been lost.[66] Paralysis remaining after one year is likely to be permanent, although modest recoveries of muscle strength are possible 12 to 18 months after infection.[62]

One mechanism involved in recovery is nerve terminal sprouting, in which remaining brainstem and spinal cord motor neurons develop new branches, or axonal sprouts.[67] These sprouts can reinnervate orphaned muscle fibers that have been denervated by acute polio infection,[68] restoring the fibers’ capacity to contract and improving strength.[69] Terminal sprouting may generate a few significantly enlarged motor neurons doing work previously performed by as many as four or five units:[38] a single motor neuron that once controlled 200 muscle cells might control 800 to 1000 cells. Other mechanisms that occur during the rehabilitation phase, and contribute to muscle strength restoration, include myofiber hypertrophy—enlargement of muscle fibers through exercise and activity—and transformation of type II muscle fibers to type I muscle fibers.[68][70]

In addition to these physiological processes, the body possesses a number of compensatory mechanisms to maintain function in the presence of residual paralysis. These include the use of weaker muscles at a higher than usual intensity relative to the muscle’s maximal capacity, enhancing athletic development of previously little-used muscles, and using ligaments for stability, which enables greater mobility.[70]


Residual complications of paralytic polio often occur following the initial recovery process.[14] Muscle paresis and paralysis can sometimes result in skeletal deformities, tightening of the joints and movement disability. Once the muscles in the limb become flaccid, they may interfere with the function of other muscles. A typical manifestation of this problem is equinus foot (similar to club foot). This deformity develops when the muscles that pull the toes downward are working, but those that pull it upward are not, and the foot naturally tends to drop toward the ground. If the problem is left untreated, the Achilles tendons at the back of the foot retract and the foot cannot take on a normal position. Polio victims that develop equinus foot cannot walk properly because they cannot put their heel on the ground. A similar situation can develop if the arms become paralyzed.[71] In some cases the growth of an affected leg is slowed by polio, while the other leg continues to grow normally. The result is that one leg is shorter than the other and the person limps and leans to one side, in turn leading to deformities of the spine (such as scoliosis).[71] Osteoporosis and increased likelihood of bone fractures may occur. An intervention to prevent or lessen length disparity can be to perform an epiphysiodesis on the distal femoral and proximal tibial/fibular condyles, so that limb’s growth is artificially stunted, and by the time of epiphyseal (growth) plate closure, the legs are more equal in length. Alternatively, a person can be fitted with custom made footwear which corrects the difference in leg lengths. Other surgery to re-balance muscular agonist/antagonist imbalances may also be helpful. Extended use of braces or wheelchairs may cause compression neuropathy, as well as a loss of proper function of the veins in the legs, due to pooling of blood in paralyzed lower limbs.[44][72] Complications from prolonged immobility involving the lungskidneys and heart include pulmonary edemaaspiration pneumoniaurinary tract infectionskidney stonesparalytic ileusmyocarditis and cor pulmonale.[44][72]

Post-polio syndrome

Between 25% and 50% of individuals who have recovered from paralytic polio in childhood can develop additional symptoms decades after recovering from the acute infection,[73] notably new muscle weakness and extreme fatigue. This condition is known as post-polio syndrome (PPS) or post-polio sequelae.[74] The symptoms of PPS are thought to involve a failure of the over-sized motor units created during the recovery phase of the paralytic disease.[75][76] Contributing factors that increase the risk of PPS include aging with loss of neuron units, the presence of a permanent residual impairment after recovery from the acute illness, and both overuse and disuse of neurons. PPS is a slow, progressive disease, and there is no specific treatment for it.[74] Post-polio syndrome is not an infectious process, and persons experiencing the syndrome do not shed poliovirus.[1]


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