Polio

1. Causative Organism
2. Clinical Signs Symptoms and Complications Method of Transmission
3. Public Health Significance
4. Prevention - Non Immunisation Methods
5. Prevention - Immunisation
6. Vaccine/s and Vaccination
7. Efficacy and Effectiveness
8. Availability
9. Dosage and Administration
10. Indications and Recommendations
11. Adverse Events
12. Contraindications
13. Risks vs Benefits

Causative Organism

Poliovirus is a member of the enterovirus subgroup, family Picornaviridae. Enteroviruses are transient inhabitants of the gastrointestinal tract, and are stable at acid pH. Picornaviruses are small RNA viruses. There are three poliovirus serotypes (P1, P2, and P3) with minimal heterotypic immunity between them (immunity to one serotype does not produce significant immunity to the other serotypes). The poliovirus is rapidly inactivated by heat, formaldehyde, chlorine, and ultraviolet light.

Signs, Symptoms and Complications

• Incubation period commonly 6–20 days with a range of 3–35 days.
• poliovirus infection is highly variable and categorised on the basis of the severity of clinical presentation.
• Up to 95% of all polio infections are asymptomatic. Infected persons without symptoms shed virus in the stool.
• Approximately 4%–8% of polio infections consist of a minor, nonspecific illness. This clinical presentation is known as abortive poliomyelitis, and complete recovery occurs in less than a week.
• Three syndromes observed with this form of poliovirus infection are upper respiratory tract infection (sore throat and fever), gastrointestinal disturbances (nausea, vomiting, abdominal pain, constipation or, rarely, diarrhoea), and influenza-like illness. These syndromes are indistinguishable from other viral illnesses.
• Nonparalytic aseptic meningitis (symptoms of stiffness of the neck, back, and/or legs), usually following several days after a prodrome similar to that of minor illness, occurs in 1%–2% of polio infections. Increased or abnormal sensations can also occur. Typically these symptoms will last from 2 to 10 days, followed by complete recovery.
• Less than 1% of all polio infections result in flaccid paralysis. The frequency of paralytic disease increases with age. Paralytic symptoms generally begin 1 to 10 days after prodromal symptoms and progress for 2 to 3 days.
• Generally, no further paralysis occurs after the temperature returns to normal. The prodrome may be biphasic, especially in children, with initial minor symptoms separated by a 1- to 7-day period from more major symptoms.
• Additional prodromal signs and symptoms can include a loss of superficial reflexes, initially increased deep tendon reflexes and severe muscle aches and spasms in the limbs or back. The illness progresses to flaccid paralysis with diminished deep tendon reflexes, reaches a plateau without change for days to weeks, and is usually asymmetrical. Strength then begins to return.
• Patients do not experience sensory losses or changes in cognition.
• Many persons with paralytic poliomyelitis recover completely and some degree of muscle function usually returns.
• Weakness or paralysis still present 12 months after onset is usually permanent.
• The post polio syndrome occurs 30-40 years after poliomyelitis. Patients experience muscle pain and exacerbation of existing muscle weakness.
  

Child with a severely deformed leg due to polio. Photo: Courtesy of World Health Organization

Method of Transmission

• Poliovirus only circulates in humans. It is spread by the faecal–oral and oral-oral (respiratory) routes.
• Infected people are most contagious shortly before and after onset of clinical illness when the virus is present in the throat and excreted in high concentration in the faeces.
• Recipients of OPV (oral polio vaccine) can also pass on poliovirus to non-immune people as the virus persists in the throat for 1 – 2 weeks and is excreted in the faeces for several weeks.

NB: New Zealand no longer uses OPV. 

Public Health Significance

The Western Pacific Region was declared Polio-free by the World Health Organisation in 2000. Polio no longer circulates in many countries, mostly due to past immunisation programmes. However; as long as it remains endemic in some countries it can be re-introduced to polio-free regions.

Hopes of worldwide eradication were dealt a major blow recently with new epidemics emerging. The first, in 2003, was based in Nigeria and spread to neighbouring countries of Chad, Sudan, Benin, Burkina Faso, Cameroon, Central African Republic, Côte d'Ivoire, Ghana, Guinea, Mali and Togo. Northern Nigerian leaders stopped the polio immunisation programme following false rumours that the vaccine contained infertility compounds and was spreading HIV. Emergency efforts in polio control appear to have stopped the spread across Africa, with no new cases in that region – outside endemic Nigeria and Niger – reported since June 2005. However, efforts to stop the 2nd and 3rd wave epidemics, which began respectively in mid/late 2004 in the Horn of Africa, and in 2005 in Indonesia, Yemen and Somalia, are ongoing.

New Zealand Epidemiology

(From 2006 Immunisation Handbook. Ministry of Health)
Deaths from polio were reported in official statistics from 1908, and notifications show large epidemics (about 1000 cases) in 1916, 1925 and 1937. Polio epidemics became more frequent and prolonged during 1948/49, 1952/53 and 1955/56. The use of the Salk (inactivated) vaccine delayed the next epidemic until 1961; this epidemic was halted by the use of the Sabin (oral) vaccine.

Following mass immunisation campaigns with OPV in 1961 and 1962 there have been no cases of poliomyelitis from indigenously acquired wild type poliovirus in New Zealand. It appears likely that poliovirus circulation was effectively stopped by these campaigns because of the high population coverage achieved.

Since 1962 there have been four definite laboratory confirmed cases of VAPP and two probable cases of VAPP identified in New Zealand. Two cases were notified in 1970, one in a vaccinee and the other in an unimmunised contact. A probable case notified in 1977 may not have been polio as no virus was isolated and the child was reported to have made a ‘good recovery’. There were two notifications in 1990, one of a child notified on suspicion who was subsequently diagnosed as having Guillain-Barré syndrome. The 1990 case reported as VAPP was an unimmunised adult contact with a high titre on serological testing, although no stool specimens were taken to support this diagnosis.

The two most recent cases in 1998 were a child who had received their second dose of OPV, and an unimmunised mother following her infant’s first dose of the vaccine. The number of cases in New Zealand was higher than would be expected from the estimated risk of VAPP in the US.

Prevention - Non Immunisation Methods

Improved sanitation and immunisation programmes have reduced the spread of polio disease.

NB: When sanitation and living standards are poor most children had acquired antibodies to all three polio virus types by age 5. However with improved sanitation polio epidemiology changed from endemic to sporadic and epidemic and the age of infection increased. Older individuals have a higher rate of paralytic disease. 

Prevention - Immunisation

Immunisation programmes offer vaccination to infants and children in every country in the world. There are two types of polio vaccines: live oral poliovirus vaccine and inactivated poliovirus vaccine. Both are highly effective in preventing poliomyelitis. Oral polio vaccine is used in countries where polio is endemic as it induces intestinal immunity and is more effective in controlling wild-virus circulation although it can, in rare cases, cause vaccine associated paralytic polio disease VAPP (approx. 1 case for every 2.4 million doses distributed). Some countries have changed from using OPV to IPV in national programmes as this risk of VAPP from OPV is no longer considered acceptable. New Zealand changed to IPV in 2002.

Availibility

• Inactivated Polio Vaccines (IPV) are used in New Zealand and is usually offered in combination with other vaccinations including DTaP-IPV-HepB/Hib (Infanrix™-Hexa, GSK) and (Infanrix™-IPV, GSK). A single IPV vaccine (IPOL, Sanofi Pasteur, MSD) is also available in limited stocks for the national schedule or for purchase as a travel vaccine.
• IPV contains poliovirus grown in either monkey kidney or human diploid cells and inactivated with formaldehyde. It contains 2-phenoxyethanol, medium199. It may contain traces of bovine serum albumin, streptomycin and polymyxin B. Polio vaccination is usually offered in combination with other vaccinations.
  

Efficacy and effectiveness

Inactivated Polio Vaccine (IPV)

• Highly effective in preventing poliomyelitis. In three-dose series IPV results in high titres of serum in 99% to 100% of patients. Immunity is prolonged, perhaps life long.

Dosage and Administration

Inactivated Polio Vaccine (IPV)

• Commonly offered as a three dose primary series in the first year of life, with a booster around school entry age.
• By injection, either on its own or in combination with other vaccines - commonly diphtheria, tetanus, pertussis, Hib and hep B vaccines.
• The dose of the IPV-containing combination vaccines is 0.5 mL.
• The IPV-containing vaccines are administered by IM injection, whereas IPV (IPOL) is given by SC injection.

Indications and Recommendations

• Infants and babies according to the national immunisation programme: 6weeks, 3 months, 5 months and 4 years old before starting school.
• Children and adults who have not yet received 4 doses.
• Travellers to endemic areas should be offered a booster if it is 10 years since last dose.
• Individuals at risk of exposure to poliovirus in the course of their employment e.g. Sewage workers can be offered 10 yearly boosters.
• Preterm infants - Extra doses of IPV-containing vaccines are not needed for babies born prematurely.
  

Adverse Events

Inactivated Polio Vaccine (IPV)

• Transient local reactions at injection site, occasional mild fever and sleepiness or crying but no serious adverse events have been reported.

Contraindications

Inactivated Polio Vaccine (IPV)

• Anyone with an anaphylactic allergy to the vaccine or any of its components.
• Patients with severe immunodeficiency disorders should be offered IPV rather than OPV. 

Oral Polio Vaccine (OPV)

• OPV is not available in NZ and has not been one the national immunisation schedule since 2002
  

Risks vs Benefits

Disease	Risk from Disease	Risk from vaccine
Highly contagious gastrointestinal infection of which humans are the only reservoir.	While many infections cause no symptoms, about 1 in 20 hospitalised patients will die and half of all surviving patients will be permanently paralysed.	IPV: local redness (1 in 3), pain (1 in 7) and swelling (1 in 10). Up to 1 in 10 has fever, crying and decreased appetite. VAPP does not occur following IPV. OPV: Fewer than 1 in 100 recipients develop diarrhoea, headache and/or muscle pain. VAPP occurs at a rate of 1 in 2.5million dose disrtibuted, or at a rate of 1/700,000 first doses.

• Link to Immunisation Handbook (2006) Chapter 8 - Poliomyelitis

50 Years of Polio Protection in New Zealand.

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