Vaccine-Preventable Diseases

Poliomyelitis

Poliomyelitis is caused by one of three serotypes of the polio virus. Depending on the serotype, it is estimated that < one in 100 or one in 1,000 infections results in paralysis and a similar proportion may result in aseptic meningitis. More than 90% of infections are asymptomatic or result in non-specific fever only.

In the pre-vaccine era, paralytic poliomyelitis was a common childhood disease in Canada and other industrialized countries. Around 11,000 people in Canada were estimated to be left paralyzed by the disease between 1949 and 1954 (paralytic and non-paralytic polio cases were reported prior to 1949). Polio incidence peaked at approximately 28 cases per 100,000 population in 1953. The inactivated poliovaccine (IPV) or Salk vaccine was introduced into Canada in 1955 and the oral poliovaccine (OPV) or Sabin vaccine in 1962. By the early 1970s, poliomyelitis was controlled in Canada mainly through immunization. The last case of paralytic poliomyelitis due to indigenous wild virus infection occurred in 1977. Wild virus imported from the Netherlands in 1978 and 1979 led to outbreaks in Alberta, British Columbia, and Ontario among closed communities that do not accept immunization for religious reasons (similar to communities affected by the outbreaks in the Netherlands). Another significant importation from the Netherlands occurred in 1993 and involved the same communities. Imported wild virus was also detected in Alberta but no clinical cases occurred. Paralytic poliomyelitis occurred almost exclusively in those < 19 years of age during the pre-vaccine period. In contrast, more than 50% of the cases reported since 1965 were aged >= 20 years; only 35% were < 15 years of age.

While the circulation of wild polio virus had been arrested in Canada for almost two decades, a polio-free status was not certified officially until 1994 when the elimination of the disease in the American Region was announced. The announcement followed a decade of intense surveillance and immunization, and came 3 years after the last indigenous wild case was reported in the region (from Peru in August 1991). Paralytic poliomyelitis has also been eliminated in several other countries, particularly in Europe. WHO continues to report progress toward achieving its target of global eradication by the year 2000. The estimated number of worldwide cases was reported to have fallen from 400,000 in 1980 to just over 100,000 in 1993, and to close to 5,000 in 1995. Global eradication will be a major achievement because it will mark the second time that a human disease has been eradicated from the world through immunization; smallpox was eradicated in 1977.

Routine immunization of children against poliomyelitis is still recommended because of the risk of imported wild virus from countries with endemic polio. This risk was highlighted most recently in Canada in March 1996; a 15-month-old boy, who had travelled to India, was found to be infected with an imported wild virus even though there were no associated clinical symptoms. Travellers to endemic regions may still be at risk and should have their immunization checked and updated when needed. Only global eradication of poliomyelitis will eliminate the need for immunization against this disease in Canada.

1998 Update:  The surveillance of AFP in children younger than age 15 years is used to monitor potential cases of paralytic poliomyelitis. AFP surveillance was initiated in 1991 through active monitoring of admissions to paediatric tertiary care hospitals in IMPACT network. In 1996, surveillance was expanded to include paediatrician-based reporting through the CPSP. All AFP reports are reviewed and analyzed by LCDC, and cases compatible with suspected paralytic poliomyelitis are referred to the national Working Group on Polio Eradication (WGPE) for further review to rule out poliomyelitis.

Table 2 shows the reporting rate and age distribution of AFP cases from 1993 to 1998. In the period following certification of polio eradication, from 1995 to 1998, the average number of AFP cases in patients younger than 15 years of age reported annually was 36 (ranging from 30 to 42 cases), which represents an average rate of 0.6/100,000 population younger than 15 years of age (ranging from 0.5 to 0.7/100,000). The AFP reporting rate in Canada remains below the World Health Organization estimated background rate of 1/100,000 population younger than 15 years of age in the absence of wild poliovirus transmission (1). However, the AFP rate in Canada has increased since the introduction of paediatrician-based reporting through the CPSP, up to 0.7/100,000 population in 1998. The current CPSP reporting network enhances the completeness of AFP surveillance by ensuring that, in addition to cases admitted to paediatric tertiary care hospitals, cases seen at other hospitals or community clinics are also reported. In addition, reporting paediatricians submit both negative reports (no cases seen) and reports of AFP cases seen.

TABLE 2: Number, reporting rate and age distribution (%) of acute flaccid paralysis cases <15 years of age, Canada, 1993 to 1998* 1993 1994 1995 1996 1997 1998 Number of cases 27 28 36 30 34 42 Rate (per 100,000)      0.45     0.47     0.60     0.50     0.57     0.70 Age group (years)†     0-1 - -   5.6   6.7 -    4.9     2-5 29.6 25.0 33.3 36.7 35.3 36.6     6-10 33.3 39.3 30.6 30.0 35.3 41.5     11- 37.0 35.7 30.6 26.7 29.4 17.1 *Provisional data for 1998; †There were 41 cases in 1998 with complete age information available

On an average, the final neurological diagnosis in reported AFP cases is Guillain-Barré syndrome in 75% of cases, transverse myelitis in 13% of cases and a variety of other paralytic illnesses in the remaining 13% of cases (Table 3). An ongoing challenge has been the need to ensure that adequate stool investigations are carried out for all AFP cases. Overall, approximately one-third of AFP case reports include a report of a timely stool investigation for the isolation of polioviruses or other enteroviruses, whereas the remainder report no adequate stool investigation or have no information. On the other hand, more than 80% of cases have had a neurological investigation (including one or more of nerve conduction studies, electromyography, magnetic resonance imaging or computed tomography scan) to support the final neurological diagnosis. In 1997, the WGPE published a protocol for the investigation of suspected cases of paralytic poliomyelitis and AFP cases. The protocol emphasizes that the single most important laboratory investigation for the diagnosis of paralytic poliomyelitis is a stool specimen collected within two weeks of onset of paralysis for the isolation of wild or vaccine strain poliovirus (2). In addition, regular reminders are issued to paediatricians and IMPACT reporters about the importance of stool investigations in all AFP cases.

TABLE 3:  Neurological diagnosis of acute flaccid paralysis cases younger than 15 years of age, Canada, 1993 to 1998* Percentage of cases Final Diagnosis 1993 (n=27) 1994 (n=28) 1995 (n=36) 1996 (n=30) 1997 (n=34) 1998 (n=42) Guillain Barré syndrome 74.1 78.6 66.7 70.0 82.4 81.0 Transverse myelitis 11.1 17.9  11.1 20.0   5.9   9.5 Other paralytic illnesses†  14.8   3.6  22.2 10.0 11.7   9.5 *Provisional data for 1998; †Includes: Encephalitis/encephalomyelitis, myelopathy, radiculopathy/radiculoneuritis and paralysis with undetermined diagnosis or etiology

REFERENCES

1. de Quadros CA, Hersh BS, Olivé JM, Andrus JK, da Silveira CM, Carrasco PA. Eradication of wild poliovirus from the Americas: acute flaccid paralysis surveillance, 1988-1995. J Infect Dis 1997;175(Suppl 1):S37-42.

2. Working Group on Polio Eradication, Bentsi-Enchill A. Protocol for the investigation of acute flaccid paralysis and suspected paralytic poliomyelitis. Paediatr Child Health 1997;2:409-12.

Polio Vaccine

Both inactivated (IPV) and live oral (OPV) poliovirus vaccines are licensed for use in Canada. However, because in the past decade all cases of polio or suspected polio have been associated with OPV and because importations of wild poliovirus have not led to transmission to anyone in Canada outside of groups that refuse immunization, only IPV is recommended for routine use in Canada. For this reason, OPV is not discussed in detail here.  

Two IPV preparations are licensed, one produced on Vero cells and the other on human diploid (MRC-5) cells. Both are formalin-inactivated products with enhanced potency and are significantly more immunogenic than the original IPV. They each contain the three types of wild poliovirus. Streptomycin, polymyxin B and neomycin may be present as preservatives. Polio vaccine is available as a single agent or in combination with diphtheria and tetanus toxoids and/or acellular pertussis vaccine (DTaP-IPV, Td-IPV).  

Efficacy and Immunogenicity  

IPV produces immunity to all three types of poliovirus in over 90% of people following two doses of vaccine given at least 6 weeks apart, and in close to 100% following a booster given 6 to 12 months later. The immune response induced in IPV vaccinees reduces the degree and duration of pharyngeal and fecal excretion of poliovirus after OPV challenge, as compared with unvaccinated children. However, IPV produces less mucosal immunity than OPV.  

Recommended Usage  

Infants and children
To avoid the risk of VAPP, exclusive use of IPV is recommended in Canada. Use of OPV alone or sequential use of IPV followed by OPV provides acceptable levels of protection, but both schedules carry the risk of VAPP in recipients or their contacts and neither offers any protective advantage to the recipient.  

Adults
Routine immunization against poliomyelitis for adults living in Canada is not considered necessary. Most adults are already immune and have a negligible risk of exposure to wild polioviruses in the Americas.  

Primary immunization with poliomyelitis vaccine is recommended only in those who are unimmunized and are at increased risk of exposure to poliovirus. Such people include the following:  

• travellers to areas of countries where poliomyelitis is epidemic or endemic;
• laboratory workers handling specimens that may contain polioviruses;  
• health care workers in close contact with individuals who may be excreting wild or vaccine strains of polioviruses;  
• unimmunized parents or child care workers who will be caring for children in countries where OPV is used.  

Schedule and Dosage  

Children
Two doses of IPV are recommended 4 to 8 weeks apart, followed by a booster dose 6 to 12 months later. When given combined with DPT (or DTaP), it is acceptable to give additional doses of IPV 4 to 8 weeks after the second dose and 4 to 6 years after the third dose for convenience of administration. However, two doses of IPV plus a booster dose are considered a complete primary series.  

For children who began their polio immunization series in a country where OPV is used, immunization may be completed using IPV; there is no need to re-start the series. Conversely, children who have been started on an immunization series with IPV and who move to an area where OPV is used may receive the necessary doses of OPV to complete their series.

Adults  
For unimmunized adults at increased risk, primary immunization with IPV is recommended as two doses given at an interval of 4 to 8 weeks with a further dose 6 months to 1 year later. Additional considerations are as follows:  

- travellers: travellers who will be departing in < 4 weeks should receive a single dose of IPV and the remaining doses later, at the recommended intervals;  

- unimmunized parents/child care workers: in those rare instances in which infants receive OPV, there is a very small risk of OPV-associated paralysis to unimmunized parents or other household contacts. It will generally not be practical for such people to be fully protected with IPV before the infant is immunized; their risk may be reduced if they are given one dose of IPV at the same time as the first dose is given to the infant. Arrangements should be made for the adults to complete their basic course of immunization.  

Incompletely immunized adults at increased risk who have previously received less than a full primary course of IPV or OPV should receive the remaining dose(s) of poliovirus vaccine as IPV, regardless of the interval since the last dose.  

Route of Administration  

IPV is injected subcutaneously according to the dose specified in the manufacturer's package insert. Combination vaccines must be administered intramuscularly because of the presence of adsorbed tetanus and diphtheria toxoids.  

Booster Doses and Re-immunization  

A need for booster doses of poliovirus vaccine in fully immunized adults has not been demonstrated. For those believed to be at particularly high risk of exposure to polio (e.g., military personnel, workers in refugee camps in endemic areas, travellers to areas where there are epidemics) a single booster dose of IPV (or OPV) might be considered. However, booster doses of vaccine are not usually necessary and are not routinely recommended for travellers.  

Outbreak Control  

If transmission of paralytic poliomyelitis caused by wild virus occurs in a community, OPV should be administered to all individuals (including infants) who have not been completely immunized or whose immunization status is uncertain. OPV is recommended because it blocks transmission by competing with wild virus in the bowel. As well, the local (gut) immunity produced by OPV is greater than that induced by IPV and is more likely to block asymptomatic infection and transmission. Thus, IPV should not be used for control of outbreaks of poliomyelitis if OPV is available.

Adverse Reactions  

The side effects of currently available IPV are normally limited to minor local reactions. As with all vaccines, anaphylaxis has been reported rarely. OPV may cause paralytic disease in recipients and incompletely immunized contacts at a rate of approximately 1 per 1 million doses distributed. Individuals travelling or living abroad whose children may be exposed to OPV should be made aware of this risk.  

Contraindications and Precautions  

IPV should not be administered to people who have experienced an anaphylactic reaction to a previous dose of IPV, streptomycin, polymyxin B or neomycin. IPV can be given without risk to those who are immunodeficient or immunosuppressed or to people who will have household or similarly close contact with such people. Less than optimal protection may be induced in those who are immunocompromised. IPV is not contraindicated in pregnancy, but its administration should be delayed until after the first trimester, if possible, to minimize any theoretical risk. If risk of exposure is imminent, IPV should be given and is always the vaccine of choice except for outbreak control.  

Selected References  

American Academy of Pediatrics. Poliomyelitis prevention: recommendations for use of inactivated poliovirus vaccine and live oral poliovirus vaccine. Pediatrics 1997;99:300-5.   CDC. Poliomyelitis prevention in the United States: updated recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR 2000;49(No. RR-5).

Cochi SL, Hull HF, Sutter RW et al. Commentary: the unfolding story of global poliomyelitis eradication. J Infect Dis 1997;175(Suppl 1):S1-3.

Duclos P. Paralytic poliomyelitis eradication: when success and forgetting may mean danger. Can J Infect Dis 1992;3:142-3.   

Hull HF, Birmingham ME, Melgaard B et al. Progress toward global polio eradication. J Infect Dis 1997;175(Suppl 1);S4-9.  

Kimpen JLL, Ogra PL. Poliovirus vaccines: a continuing challenge. Pediatr Clin N Am 1990;37:627-47.  

Melnick JL. Poliomyelitis: eradication in sight. Epidemiol Infect 1992;108:1-18.  

Modlin JF, Halsey NA, Thomas ML et al. Humoral and mucosal immunity in infants induced by three sequential inactivated poliovirus vaccine-live attenuated oral poliovirus vaccine immunization schedules. J Infect Dis 1997;175(Suppl 1):S228-34.

Plotkin SA, Orenstein WA. Vaccines. 3rd edition. Philadelphia: W.B. Saunders Company, 1999.  

Sabin AB. My last will and testament on rapid elimination and ultimate global eradication of poliomyelitis and measles. Pediatrics 1992;90:162-9.

Strebel PM, Sutter RW, Cochi SL et al. Epidemiology of poliomyelitis in the United States one decade after the last reported case of indigenous wild-virus associated disease. Clin Infect Dis 1992;14:568-79.  

Vidor E, Meschievitz C, Plotkin S. Fifteen years of experience with Vero-produced enhanced potency inactivated poliovirus vaccine. Pediatr Infect Dis J 1997;16:312-22.

Wright PF, Kim-Farley RJ, de Quadros CA et al. Strategies for the global eradication of poliomyelitis by the year 2000. N Engl J Med 1991;325:1774-9.