Polioviruses occur as three serotypes. They are highly conta- gious and paralysis can occur. Infection of one person may lead to infection of other household members or others in close con- tact in 73–96% of the cases, depending on the contactee’s age. The virus is spread by the fecal-oral route with some trans- missions being oral-oral. The virus ﬁrst replicates in the mucosal membranes of the pharynx and gastrointestinal tract, then, 3–35 days later, in the blood stream and, to a lesser degree, in the central nervous system. Polio was the dreaded summer disease up until the 1960s. While up to 95% of cases are subclinical, paralytic poliomyelitis accounted for 2% of the cases. From 2–5% of young children and from 15–30% of adults who acquired paralytic polio died. Before the development of preventive vaccines, treatment of paralytic polio consisted of medications, iron lungs, limb and back braces, and rehabilitation therapy.
The inactivated poliovirus vaccine (IPV) was developed by Jonas Salk in the early 1950s and was introduced for use in the United States in 1955. Although this vaccine was shown to be safe and efﬁcacious, its use quickly declined after intro- duction of the oral poliovirus vaccine (OPV) in the early 1960s.
An enhanced version of the inactivated vaccine was developed in 1978 (182) and later licensed in the United States in 1987. This more potent formulation results in improved immunity in children and adults (183). In children given the three dose regimen, 99–100% developed antibody responses to all three types of poliovirus two months after the second dose (184). Sig- niﬁcant increases in antibody concentrations were observed after administration of the third dose. In separate clinical studies, 99–100% of subjects developed protective antibodies after three doses (185,186). The use of IPV results in less gas- trointestinal immunity than OPV (163), although the newer enhanced formulation induces a signiﬁcant degree of mucosal immunity that has been demonstrated to produce effective protection (185,188). The duration of immunity induced by IPV is unknown, but is thought to be long-term (Table 4.5). A study in Sweden using 4 doses of less potent IPV indicated that over 90% of vaccine recipients had persistent antibodies after 25 years (189).
The oral polio vaccine was ﬁrst licensed in the United States in 1963 and consists of live attenuated strains of the three serotypes of poliovirus, all grown in monkey kidney cell culture. In the 1960s, OPV quickly became the favored vaccine because of its ease of oral administration, consistent produc- tion of gastrointestinal immunity, expected long-lasting immunity, and spread of the vaccine virus to unvaccinated contacts (190). After three doses of OPV, over 95% of recipients produce immunity to all three serotypes of poliovirus (184). This immunity is considered to be long-lasting, and likely life- long. Because of fecal shedding of the vaccine virus after OPV administration, this vaccine can immunize unvaccinated con- tacts (191). However, viral shedding of mutated virus may also lead to vaccine-associated paralytic poliomyelitis (VAPP) in unvaccinated contacts, particularly the immunosuppressed.
Since the introduction and widespread use of the two polio vaccines, the number of poliovirus infections and compli- cations has dramatically decreased. In 1994, the Western Hemisphere was certiﬁed to be free of indigenous wild poliovi- rus (192). The last case of indigenously acquired wild poliovi- rus infection in the United States occurred in 1979 (193).
a Immunogenicity appears to be variable for OPV, particularly in underdeveloped areas. Factors associated with 1) maternal antibody level; 2) season; 3) diarrhea at time of vaccination; 4) exposure to other recipients; and 5) breastfeeding.
Since that time, an average of 8–9 cases of paralytic polio have been reported each year in the United States due to the use of the oral, live attenuated polio vaccine (OPV) (194). VAPP occurs in one case per 2.4 million doses, but is more common after the ﬁrst vaccine dose (one case per 750,000 ﬁrst OPV doses) (194).
The World Health Organization developed a strategy for global eradication of poliomyelitis by the end of the year 2000, which unfortunately was not met. Signiﬁcant progress has been achieved toward that goal, with a 90% reduction of
poliomyelitis cases between 1988 and 1996 (195). In 1988, poliovirus was found on every continent except Australia. However, in 1998, only three major foci of disease remained including the regions of South Asia, West Africa, and Central Africa (196). Worldwide, there were 2979 new cases in 2000 and 537 in 2001 (197). Global eradication continues to be elu- sive as local customs and fear affect vaccination rates. As an example, parents in Nigeria recently were refusing to allow children to be vaccinated for fear that the vaccine might con- tain HIV or make their children infertile. The vaccine is viewed as a Western ploy to curb population growth. Nigeria is one country where polio eradication is in danger of failure (198).
In 2002, India had over 85% of the new cases of polio worldwide despite national immunization days and house-to- house visits to administer OPV (199).
Vaccine-associated paralytic poliomyelitis (VAPP).
Between 1980 and 1994, 125 cases of VAPP were re- ported in the United States: 49 cases occurred in healthy vaccine recipients; 40 cases developed in healthy contacts of the vaccine recipient; 23 cases oc- curred in immunodeﬁcient vaccines; 7 cases developed in immunodeﬁcient contacts of vaccine recipients; and the remaining 6 cases developed in community con- tacts (194). VAPP more frequently occurs in adults, im- munodeﬁcient persons, and those receiving the ﬁrst dose of OPV (187). Because of the diminished risk for wild poliovirus disease in the United States, the risk for VAPP is now considered to be less acceptable (194). It is now recommended that, to eliminate the risk for VAPP, an all-IPV schedule be used for routine child- hood vaccination in the United States. All children should receive four doses of IPV: at age 2 months, age 4 months, between ages 6 and 18 months, and between ages 4 and 6 years.
Inactivated polio vaccine (IPV). No serious adverse ef- fects have been reported with IPV. This vaccine contains trace amounts of polymyxin B, neomycin, and strepto- mycin and may cause hypersensitivity reactions in per- sons allergic to these substances.
Oral poliovirus vaccine (OPV). OPV has no serious adverse effects other than VAPP.
Guillain-Barré syndrome. Evidence indicates that nei- ther OPV nor IPV increases the risk for Guillain-Barré syndrome (194).
Oral poliovirus vaccine (OPV). If available, OPV may be used only for the following special circumstances:
Mass vaccination campaigns to control outbreaks of paralytic polio.
Unvaccinated children who will be traveling within 4 weeks to areas where polio is endemic or epidemic. Children of parents who do not accept the recom-
mended number of vaccine injections; these children may receive OPV only for the third or fourth dose or both. In this situation, health-care providers should administer OPV only after discussing the risk for VAPP with parents or caregivers.
As a result, OPV supplies are expected to be very lim- ited in the United States after inventories are depleted (200).
Monkeyvirus SV40 and rare cancer (pleural me- sothelioma). High levels of SV40 cause tumors when injected in rodents. There is no association between prior childhood vaccination of strains of SV40 in polio vaccine and pleural mesothelioma. Persons least likely to have been immunized (age >75 yrs) were those with increased rates of plural mesothelioma (201).
Pleconaril. Pleconaril was used to treat three acute ﬂaccid paralysis cases: two vaccine-mediated and one wild- type with a good clinical and virological response (202). Immunocompromised. Live vaccines are contraindi- cated in people who are infected with HIV because of the risk of infection from attenuated microorganisms. Beneﬁts of OPV outweigh the risks and should contin- ue to be used in countries where HIV infections are endemic.