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Institute of Medicine (US) Vaccine Safety Forum; Howe CJ, Johnston RB, editors. Options for Poliomyelitis Vaccination in the United States: Workshop Summary. Washington (DC): National Academies Press (US); 1996.

Cover of Options for Poliomyelitis Vaccination in the United States

Options for Poliomyelitis Vaccination in the United States: Workshop Summary.

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History and Current Status


Polio is a disabling and occasionally fatal disease that has been known since ancient times. Its devastating effect in the United States was most dramatic in the 1950s, when large hospital wards were filled with patients on respirators. The disease reached its peak incidence in the United States in 1952, with 20,000 cases of paralytic poliomyelitis. In developing countries today polio remains a major cause of disability.

Progress toward the control of polio by immunization was possible only after the successful propagation of poliovirus by researchers: Landsteiner and Popper in monkeys in 1909; Sabin and Olitsky in human brain tissue in 1936; and Enders, Weller, and Robbins in human non-nervous system tissue in 1949. Work proceeded on both a killed or inactivated vaccine and on a live attenuated vaccine. The Salk inactivated vaccine (IPV) was the first to be ready for field trials. Its effectiveness at preventing disease resulted in its rapid licensure (1955 in the U.S.) and use worldwide and led to a dramatic drop in the incidence of paralytic poliomyelitis. The Sabin live attenuated vaccine (OPV) became available in the 1960s—the monovalent vaccine in 1961 and the trivalent vaccine in 1963. Because of its greater ease of administration, lower cost, and better induction of immunity in the intestinal tract, OPV became the vaccine of choice in many countries. An enhanced-potency IPV, licensed in 1987, has had limited use in the United States because primary reliance on OPV has been the longstanding U.S. policy.

Contributing to the sustained interruption of wild-type polio virus circulation in the United States are high immunization levels and the spread of the OPV strains of virus to unimmunized populations. Since the 1980–1981 school year, the levels of immunization with three or more doses of OPV at the time of school entry, about 5 years of age, have been greater than 90 percent. Immunization levels among U.S. preschool-age children, though, are substantially lower. In 1993, the reported coverage rate among 19- to 35-month-old children (median age, 27 months) for three doses of OPV was 79 percent. This translates into approximately 1.25 million 19- to 35-month-old children in 1993 who had not received a full primary series of OPV. The importance of the spread of the vaccine strains of virus in maintaining immunity to polio among unvaccinated inner-city populations was investigated by Chen and colleagues in emergency rooms in Houston and Detroit in 1990–1991. Their unpublished data suggest that spread of the OPV strains plays a role in enhancing population-based immunity among unvaccinated children in inner cities.

The U.S. has several surveillance systems for polio disease: (1) routine reporting through the morbidity reporting system for contagious diseases; (2) the Vaccine Adverse Event Reporting System (a passive surveillance system, stimulated by provider letters, to which vaccine-associated cases of polio may be reported); (3) the enterovirus surveillance system, which collects reports from about 30 states and one county on their isolation of enterovirus; (4) the large linked database system (LLDB), a system in four large health maintenance organizations in the western United States that covers about 500,000 children from birth to age 6 and includes surveillance for paralytic illness; (5) investigation of clusters of cases of paralytic polio; and (6) reports from investigators who isolate the virus and call CDC to request characterization of wild-type poliovirus. Current plans are to continue the system as it is structured and to continue to stimulate reporting through publicity.

Recent Experience

Between 1975 and 1992, 189 confirmed cases of paralytic poliomyelitis disease were reported in the United States. These included 10 epidemic cases, 152 vaccine-associated cases, 14 imported cases, and 13 cases of indeterminate origin. Since 1980, no epidemic or indigenously acquired cases of paralytic poliomyelitis caused by wild-type virus have been detected in the United States. During the 5-year period from 1990 through 1994, only one case of poliomyelitis importation was reported, an intentional importation of a 30-month-old who was brought to the United States for treatment following the onset of disease in Nigeria.


“It was the day of my ninth birthday party, and they were putting me in the ambulance, when I remember hearing one of my friends saying, “Where is Sandy going? Isn't that Sandy? Today's her birthday party.” My mother never even had a chance to call off my birthday party. . . . I remember hearing somebody say, “If this doesn't stop, if her fever doesn't break, we're going to have to put her in an iron lung.” And I woke up the next day, my temperature had broken, and I was completely paralyzed from my neck down. I couldn't even move my neck. . . . And they sent me down to Warm Springs, Georgia, where I went for three summers in a row, where they rehabilitated me, they did corrective surgery on me, and they got me walking at least to where I could get around with braces and crutches. . . . I was so happy that there would never be any more paralysis from polio around the world again, if people used this vaccine. I was so grateful that nobody in my family would ever have to experience the things that I was going through and probably would have to go through the rest of my life.”


From a March of Dimes video commemorating the 40th anniversary of the release of the Salk polio vaccine.

One case of paralytic poliomyelitis theoretically can represent hundreds of individuals infected with the virus. Estimates vary from 50 to 1,000 subclinical infections for each case of paralytic disease diagnosed. It is particularly difficult to ascertain the risk of spread following importation when the level of immunity in the population is high.

Vaccine-Associated Paralytic Poliomyelitis

Between 1980 and 1992, a total of 109 cases of vaccine-associated polio were reported in the United States, an average of 8.4 cases per year. 2 During this interval, 262 million doses of OPV were distributed. The overall risk of VAPP was thus 1 in 2.4 million doses distributed. The CDC estimates that the risk of VAPP is 1 in 750,000 first doses compared with a risk of 1 in 5.8 million for subsequent doses. The risk of VAPP after the first dose in immunologically normal vaccine recipients was 1 in 1.5 million first doses. The ratio of vaccine-associated polio cases to total doses of OPV distributed has remained constant since the 1960s (Nkowane et al., 1987; Strebel et al., 1992).


“I remember getting up in the middle of the night and wanting a drink of water because it was so hot and I was just kind of burning up. I think I went upstairs and got a drink and started to walk back down the stairs, and my legs caved in, and I fell down the stairs. . . . When I first got it, the doctors gave me 10 days to live, and I could only move one finger, and I was just a very, very sick little girl in the polio wards. . . . I had to relearn how to walk with crutches, very similar to the ones I have, and braces, very similar to the ones I'm wearing. I also wear a back brace, and that's the equipment I've worn all my life, since I was four years old. . . . I just think that it was a modern miracle. I think it was just a wonderful thing that Salk did for the world.”


From a March of Dimes video commemorating the 40th anniversary of the release of the Salk polio vaccine.

All of the immunologically abnormal vaccine recipients were found to be immunologically abnormal only after they developed VAPP, and none were found to be infected with the human immunodeficiency virus (HIV). The majority of cases of VAPP among immunodeficient individuals result from congenital immunodeficiencies (about 70 percent of these are B-cell abnormalities). One case was found to be associated with prolonged steroid use.

Most of the cases of polio in children who have recently received OPV (referred to as recipient cases) occur in the first year of life; such children account for 93 percent of all recipient cases. In contrast, most of the cases of polio resulting from contact with recent vaccinees (contact cases) occur in adolescents and adults. Of the contact cases, 73 percent developed in individuals older than 19 years of age. The majority of individuals with VAPP had not received a primary series of at least three doses of IPV or trivalent OPV before developing their paralytic illness.

Theoretically, vaccine-associated polio among contacts, which occurs principally in adults, should decrease as immunity levels among adults increase. Among first time U.S. Army recruits during September and October 1989, more than 97 percent had antibodies to type 1 poliovirus, more than 99 percent had antibodies to type 2, and more than 85 percent had antibodies to type 3. Type 3 virus is the most common cause of vaccine-associated polio. The fact that about 15 percent of recruits were seronegative to type 3 suggests that vaccine-associated polio among contacts can remain a problem.

Annually, about three cases of VAPP occur among normal recipients, three cases occur among normal contacts, and two cases occur among those who are immunologically abnormal. The recipient cases could possibly be prevented by the use of two doses of IPV before receipt of OPV. It is more difficult to predict the effect on immunologically abnormal recipients of a sequential IPV-OPV schedule, because some cases of polio may be prevented by delaying OPV administration if the immunological problem is detected during that period of time. It is even more difficult to predict the impact of a sequential schedule on contact cases. The data suggest that prior IPV decreases fecal shedding of OPV virus; to the extent that it does, some contact cases may be prevented. However, the more shedding is reduced, the less potential benefit people in undervaccinated areas will receive from the transmission of OPV virus.

Most confirmed cases of VAPP are severe. In the acute phase, about 40 percent involve three or more limbs or the need for respiratory assistance, or both, and in many other affected individuals significant involvement of one or two limbs is found. Questions remaining about VAPP include the following: Why are there several cases in immunologically normal recipients each year in the United States? Are some hosts more susceptible than others and, if so, why? Is prior receipt of IPV effective in reducing vaccine-associated disease after OPV? Is VAPP prevented by systemic or mucosal immunity, either by protecting the systemic immune system or by reducing virus shedding? How many of the 8 to 10 cases of VAPP annually can be prevented?


David Salamone received the oral polio vaccine as an infant. Within days, he had a high fever and within weeks he could no longer crawl or use his legs. He had contracted poliomyelitis from his vaccine. David was eventually found to have Bruton's agammaglobulinemia, a rare immunodeficiency that renders him vulnerable to infections and makes it hazardous for him to receive any live vaccine. Today, at age 5, David can walk with the help of a brace, but he tires easily and falls frequently. He makes weekly visits to a physical therapist, whom he calls his “toy doctor” because of the playthings used in his therapy. He also regularly sees a neurologist, a physiatrist, a rheumatologist, and an orthopedist. David's parents try to allow him to be as much like other children as possible. He loves to play in the park, although much of the time he is watching other children at play. As he interacts with more children in school, he asks his parents why he is not chosen for teams and is always last in races. His parents try to maintain a positive approach for him, but they know that he faces years of therapy and surgery. The family believes that polio vaccination policy should be changed to rely primarily on the inactivated polio vaccine to prevent other children and families from suffering as they have.


Based on a presentation by John Salamone.


Latin America

In September 1985, when polio remained endemic in 15 of 37 member countries, the Pan American Health Organization determined that poliomyelitis must be eradicated. The strategy consisted of (1) achieving and maintaining very high levels of immunity in the population at risk (children less than 5 years of age), (2) surveillance for suspected cases, and (3) response to these cases. This strategy was implemented in all countries of the region in the succeeding years. Achieving and maintaining high levels of immunity were accomplished through the implementation of national immunization days (NIDs), during which all children under age 5, regardless of their previous vaccination status, received doses of OPV in two rounds about 6 to 8 weeks apart. This strategy was pioneered in Cuba in the early 1960s with the assistance of Albert Sabin. A surveillance network of reporting sites and laboratories was organized. About 10 laboratories were strategically located in several countries in the region. Data from the laboratories indicated that the genotypes of different poliovirus strains were not migrating frequently from one subregion to another. Therefore, a complementary “mopping up” strategy was developed, consisting of house-to-house vaccination in the areas where polio transmission persisted.

In 1987, cases of polio had been reported from nearly every district with the exception of the southern part of Argentina and Chile. In 1989, about 800 of 1,400 districts in Latin America were considered high risk and were targeted for the house-to-house mopping up technique. After that, polio transmission was largely interrupted. Following the mopping up of 1988, 1989, and 1990, only two outbreaks occurred in 1991. One of these outbreaks consisted of seven cases in the area around Cartagena, Colombia, with the onset of the last case there occurring in May 1991. The last reported case was in Peru in August 1991. In Latin America, one case of VAPP is reported per 1.5 million to 2.2 million distributed doses.

An international commission for the certification of polio eradication, chaired by Frederick Robbins, established the following criteria for certification: (1) a good surveillance system, with units reporting weekly on the presence or absence of cases of acute flaccid paralysis (AFP); (2) investigation of these cases within 48 hours; (3) fecal specimen collections sent to a network of laboratories with good quality control; (4) the presence of AFP at a rate of at least one case per 100,000 children under age 15 per year; (5) no confirmed cases of paralytic polio within a period of at least 3 years; (6) no wild-type virus isolated from contacts of patients with AFP, and if necessary, from the environment; and (7) permanent program evaluation and mechanisms for dealing with importation of poliovirus by travelers.

Today, the reporting system for AFP encompasses more than 25,000 health facilities, and 80 to 85 percent of them report weekly and on time. Over the period under study and until the commission met in September 1994, more than 35,000 stool samples had been collected from cases and contacts. Wild-type virus was last isolated in 1991. The evidence led the commission to declare on September 29, 1994, that wild-type polio transmission had been interrupted in the Americas. Because of the risk of importation of the virus from other geographic areas, the commission recommended that surveillance and vaccination for polio should continue at the same level as during the eradication period.


Lenita Schafer took her 3-month-old daughter for her immunizations, including OPV, in October 1988. Six weeks later, while cooking Thanksgiving dinner, Mrs. Schafer fell and has not been able to walk since then. She had contracted polio from exposure to her daughter's vaccine. Mrs. Schafer has been unable to return to work since her paralysis. Her condition has affected the entire family. Intimate relations with her husband are difficult. She is unable to perform her share of many household tasks, gardening, and lawn work. She cannot travel independently and requires her husband or another companion for assistance. Because she cannot exercise her lower body, she has gained a great deal of weight and has enrolled in a weight loss program. She frequently has back pain and muscle spasms in her legs. Her young daughter does not yet understand why her mother cannot participate in some activities with her. Mrs. Schafer believes that no one should be immunized without their knowledge, as she was, in effect, by exposure to her daughter after vaccination, and thus calls for increased awareness of IPV for polio immunization.


In Canada, vaccine policy recommendations are made by the National Advisory Committee on Immunizations. However, because health care policy is a provincial decision, each province determines whether to implement the national recommendations. As a result, vaccine delivery systems and the type of vaccines used vary by province. Both IPV and OPV have been used in Canada, and the national recommendations have always sanctioned either vaccine as acceptable.

The last identified case of indigenous wild-type polio in Canada was in 1977. The last imported case was in 1988, in a Pakistani child born in Toronto and living in a large apartment complex with many recent immigrants from Pakistan. The isolated strain was determined to be typical of that found on the Indian subcontinent.

Canada has had two incidents of importation traceable to the Netherlands-based Dutch Reformed Church, which does not accept vaccination. Because this church has an active missionary program with frequent international travel, importation from this source could be an ongoing problem until polio is eradicated worldwide. During a 1979 outbreak, a total of 11 cases of disease were reported from three provinces: Alberta and British Columbia (which used OPV), and Ontario (which used IPV). In 1993, wild-type virus was detected in several families in Alberta after visits to the Netherlands following a Dutch outbreak, but wild-type virus was not detected in small studies in either Ontario or British Columbia. In both of those outbreaks, no disease and no viral spread were detected in the vaccinated communities in or near the areas where Dutch Reformed Church members lived.

From 1965 to 1993, 19 cases of VAPP occurred in Canada; the majority were contact cases, unlike the experience in the United States. Since 1988, all of the polio cases in Canada have been vaccine associated.

Some Canadian provinces have made the decision to change the polio vaccine of primary reliance. The switch has been facilitated by two factors. First, a quadrivalent DTP-IPV vaccine has been available in Canada for more than 20 years; more recently, a pentavalent combination that uses the DTP-IPV vaccine as the diluent for the tetanus toxoid conjugate of theHaemophilus influenzae type b vaccine (Hib) has become available. One of the concerns in this switch has been the issue of immunologic interactions with combination vaccines. Postmarketing surveillance for vaccine failures is ongoing. The second factor facilitating a switch was the ability to introduce IPV as a cost-neutral change to the vaccine program. Although the unit dose is more expensive, the higher wastage rate in Canada of OPV in comparison with IPV (an estimated 50 percent versus 10 percent) made the change cost neutral. Ontario switched from IPV to OPV in 1989 and then back to IPV, the change necessitated by the temporary lack of an IPV supply; implementation of the policy change was relatively easy. The combination product (DTP, IPV, and Hib) is now used in all provinces except Quebec and Manitoba. Quebec has made the decision to switch to the combination product, but Manitoba has not yet made a decision. IPV usage for children in Canada went from about 40 percent in earlier years to more than 70 percent by the end of 1985.


As mentioned earlier, decisions about immunization policy in one part of the world are dependent on the situation internationally. The United States and other countries in the Western hemisphere must take into account the possibility of importation from areas where polio disease has not been eradicated. The global eradication of polio means the documentation that no cases of polio caused by wild-type poliovirus have occurred, that wild-type poliovirus transmission has ceased, and that no wild-type poliovirus has been found, despite intensive efforts to do so. This has been accomplished in the Americas, and the World Health Organization (WHO) goal for global eradication is the year 2000. The basic strategies for global eradication are similar to those demonstrated to be effective in the Americas, as described above. OPV has been the vaccine of choice for use in global eradication programs.

The benefits (both direct and indirect) of polio eradication efforts include (1) reductions in disease and disability; (2) financial benefits (the estimated potential savings of the cost of vaccine and its administration are at least $230 million per year in the United States and $1 billion globally); (3) improved primary health care in general, including better control of measles and neonatal tetanus, especially by using NIDs; (4) development of a laboratory network as the basis for tackling other diseases of public health importance; and (5) better disease surveillance and the consequent improved ability to identify and address other public health problems.

The global level of routine immunization with three doses of OPV in children by 1 year of age increased from about 10 percent in the early 1980s to a peak of 85 percent in 1990 and has been sustained at about 80 percent since then. The number of reported cases of polio declined from 35,000 in 1988 to an estimate of less than 7,000 in 1994. On the basis of data from 1994, the Americas have been polio-free for 3 years; emerging polio-free zones elsewhere around the world include western and central Europe, China, parts of north Africa and southern Africa, and the Arabian Peninsula. The highest proportion of reported cases of polio (67 percent) in 1994 was in the WHO's southeast Asia region, which comprises the Indian subcontinent and Indonesia; India and Bangladesh account for almost all of this, with more than 60 percent of the cases reported worldwide in 1994 being in India.

A substantial proportion of the estimated costs of polio eradication are paid by countries where polio is endemic, rather than by external donor organizations. Thus, it takes a high level of commitment and political will on the part of countries where polio is endemic to implement polio eradication strategies. The estimated external need is about $500 million over the next 5 years, or about $100 million per year in external donor support. About 80 percent of this is for the purchase of OPV. The main obstacles to polio eradication are the lack of funds for vaccine and technical support; insufficient political commitment in several countries where polio is still endemic; falling levels of routine immunization in a number of countries in sub-Saharan Africa; and political unrest, which remains one of the biggest unknowns in terms of achieving the objective of eradication by 2000.

Eradication efforts in countries where polio is endemic are proceeding. The People's Republic of China began implementing polio eradication strategies in 1991, began provincial immunization days soon thereafter, and has now carried out NIDs for 2 years in succession (1993 and 1994). Polio is at record low levels in China. WHO's western Pacific region, which includes the People's Republic of China, has a goal of eliminating polio by the end of 1995. In response to the high proportion of polio cases in India, that country is planning its first NIDs in 1995 and 1996. Some parts of Africa still lack major efforts at eradication, but at recent meetings between the United Nations Children's Fund (UNICEF), WHO, and other groups, planning for NIDs has begun.

WHO has expressed two primary concerns about the possibility of a change in polio vaccination strategies in the United States. The first is that a change in policy could undermine financial support for the global polio eradication effort. The U.S. government has been one of the principal supporters of eradication, but substantially more funds will be needed. WHO officials fear that a change to the domestic use of one or more doses of the more expensive IPV could result in reduced U.S. funding for the global effort. WHO's second concern about a strategy shift is that countries where polio is endemic might follow the lead of the United States and decrease their reliance on OPV before it is appropriate for them to do so. In the past, U.S. immunization policy has had a strong influence on physicians and public health professionals in developing countries. The WHO leadership believes that eradication of polio in countries where it is endemic can only be accomplished through mass vaccination with OPV and that a change to IPV in those countries could jeopardize the global eradication effort.

Some participants expressed the belief that, if it were made clear that the United States is considering a change only after more than 10 years without indigenous wild-type polio and that the concern is primarily one of safety rather than efficacy, the impact on other countries could be lessened. Others noted that a sequential schedule of immunization with OPV and IPV might have the least negative global impact on polio eradication efforts, because OPV would still be recommended as part of the vaccination program.



The material in this section is adapted from presentations by Frederick Robbins and Walter Orenstein and comments by other workshop speakers or participants.


Of these, 41 were immunologically normal vaccine recipients, 38 were normal contacts of immunologically normal vaccine recipients, 7 had community-acquired cases of polio, and 23 were vaccine recipients or contacts who were immunologically abnormal (17 vaccine recipients and 6 contacts).


The material in this section is adapted from presentations by Ciro de Quadros and Ronald Gold and comments by other workshop speakers or participants.


Based on a presentation by Lenita Schafer.


The material in this section is adapted from a presentation by Stephen Cochi and comments by other workshop speakers or participants.

Copyright 1996 by the National Academy of Sciences . All rights reserved.
Bookshelf ID: NBK231547


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