Epidemiologic Notes and Reports Follow-Up on Poliomyelitis -- United States, Canada, Netherlands

{From the July 27, 1979, MMWR}

No new cases of epidemic-associated poliomyelitis have been reported to CDC during the past month. Two cases previously reported as suspected have now been confirmed, bringing the 1979 total of confirmed cases in the United States and Canada to 17. Fourteen of these cases (all paralytic) occurred in unvaccinated Amish persons; 2 (both nonparalytic) were in unvaccinated non-Amish persons, who lived in or near an Amish area; and 1 case (paralytic) occurred in an Amish infant, who received oral poliovirus vaccine 5 days before becoming ill. In the latter case, the patient had laboratory evidence of recent infection with both type 1 and type 2 poliovirus; the other 16 cases were clearly due to a wild (type 1 poliovirus. These 17 cases have been reported from 4 different states (Pennsylvania, 8 cases; Iowa, 3; Wisconsin, 3; Missouri, 1) and Canada (2). Immunization campaigns for the Amish are continuing; at least half of the nation's Amish have now received 1 or more doses of oral poliovirus vaccine.

Antigenic marker tests, consisting of (a) the van Wezel Method, using cross-absorbed rabbit antisera against vaccine and nonvaccine (wild) poliovirus strains and (b) the modified Wecker method, using guinea pig antisera against vaccine strains, have been performed on the poliovirus type 1 strains isolated from 5 U.S. cases and from a household contact of a sixth case. All isolates were nonvaccine-like in their antigenic characteristics.

The type 1 poliovirus isolated from the first 1979 poliomyelitis patient (an Amish female from Pennsylvania) shows a resemblance to a wild type 1 strain isolated in Kuwait in 1977 (1). Type 1 strains from cases occurring in the 1978 epidemic in the Netherlands and Canada also showed a resemblance to the Kuwait poliovirus strain (1).

Epidemiologic information also links last year's poliomyelitis epidemic in the Netherlands and Canada with this year's outbreak in the United States and Canada. During the 1978 outbreak, members of the affected religious group traveled from the Netherlands to Canada, where cases subsequently appeared. An Amish family from an Ontario town 15 miles from the affected area moved in late summer 1978 to the Pennsylvania town where the first U.S. Amish case subsequently occurred, in January 1979. There were also other, less well-defined contacts between Amish persons in Ontario and Pennsylvania.

Reported by Dr. A. van Wezel and Dr. van Zermarel, Rijks Institute voor der Volksgezondheit, the Netherlands; S Acres, MD, Dept of National Health and Welfare, Ottawa; State Epidemiologists from Iowa, Missouri, Pennsylvania, and Wisconsin; Virology Div, Bur of Laboratories, and Viral Diseases Div, Bur of Epidemiology, CDC.

editorial note: Both laboratory and epidemiologic information have suggested a link between the poliovirus type 1 strain from the 1979 outbreak in the United States and Canada with the type 1 strain responsible for last year's outbreak in the Netherlands and Canada. The onset of illness in the last case occurring in Canada in 1978 was in August, more than 4 months before the onset of illness in the first 1979 case, which occurred in Pennsylvana. Nearly 3 months elapsed before the next 1979 cases occurred, and these were also in Pennsylvania. These data suggest that the wild poliovirus circulated inapparently through several generations without causing paralytic disease. The absence of new cases of paralytic poliomyelitis reflects, in part, the success of the multi-state immunization campaigns for the Amish; the possibility of new cases remains, because the wild type 1 poliovirus may continue to be excreted by some infected persons throughout the summer months. However, the risk of additional cases is diminishing as more of the susceptible Amish persons receive vaccine. reference

1. van Wezel A: Personal communication.

   Editorial Note

Editorial Note 1997: MMWR should never again publish an article describing a contemporaneous outbreak of polio in the United States. Although it was not known at the time the 1979 MMWR articles were published, these articles describe the last outbreak of polio in the United States. The 1979 outbreak occurred in unvaccinated Amish persons living in Iowa, Missouri, Pennsylvania, and Wisconsin. Overall, 15 cases of illness caused by wild poliovirus type 1 occurred among U.S. citizens: all 10 paralytic cases occurred among unvaccinated Amish persons; three cases of transient paralysis occurred among unvaccinated Amish persons; and two nonparalytic cases occurred among unvaccinated members of the Mennonite church who were in frequent contact with Amish persons. Epidemiologic and virologic evidence indicated this outbreak resulted from importation of poliovirus from the Netherlands through Canada (Ontario), where outbreaks had occurred during 1978 in members of religious groups with objections to vaccination. Intensive studies in an outbreak-affected area where there were extensive contacts between Amish and non-Amish persons indicated that existing immunity levels provided an effective barrier to extensive circulation of poliovirus in the general community. Investigation and control of the outbreak involved exceptional cooperation between local and state officials in the 21 states with Amish populations and CDC. As highlighted in the May 25, 1979, MMWR article, CDC considered the entire U.S. Amish population to be at risk for polio and recommended vaccination of all Amish persons, including adults. Epidemiologic aspects of the investigation were coordinated by CDC Epidemic Intelligence Service officers Marjorie Pollack, M.D., and Melinda Moore, M.D., under the supervision of Larry Schonberger, M.D., of CDC's Division of Viral Diseases (which then was responsible for polio surveillance). The programmatic efforts to reach and vaccinate Amish populations were coordinated through the Division of Immunization and state immunization programs, and used the efforts of many CDC public health advisors. Vaccination efforts involved extensive contacts with Amish groups in the 21 states and ultimately resulted in vaccination of approximately one half of Amish persons in the United States.

Another notable feature of this outbreak was the very close collaboration between epidemiologists and the laboratory. Using oligonucleotide mapping (the newest tool available at the time), CDC laboratory scientists Milford Hatch, Ph.D., and Olen Kew, Ph.D., were able to show that the virus responsible for illness in the United States was identical to the virus that had caused outbreaks in the Netherlands and Ontario, Canada. Subsequent development of more sophisticated techniques such as genomic sequencing further confirmed the link. This was one of the first instances of use of "molecular epidemiology" at CDC and heralded a collaboration between epidemiologists and laboratorians that has been a hallmark of the global polio-eradication program.

The 1979 outbreak demonstrated both the tremendous progress to date in achieving protection of the U.S. population but also the fact that polio could find a way to reach the remaining pockets of susceptible persons in the country. In addition, the outbreak made clear the necessity of taking a global approach to polio.

During the first half of the 20th century, paralytic polio was a major cause of illness and public concern in the United States; reported cases increased annually and peaked at approximately 20,000 reported cases in 1952. The introduction of inactivated poliovirus vaccine (IPV) in 1955 and the subsequent introduction of oral poliovirus vaccine (OPV) in 1961 had a dramatic impact on the occurrence of disease, with the numbers of reported cases and outbreaks progressively decreasing to very low levels by 1970.

Throughout the 1970s, there was continued evidence of possible circulation of wild poliovirus in the United States. During the decade, 17 cases of polio were imported from other countries and for 30 cases of paralytic polio, no foreign source could be determined (endemic cases). Since the reports in 1979, no endemic cases have been reported in the United States, although imported cases (on average less than one per year, predominantly from Mexico) continued to occur throughout the 1980s.

In 1985, the Health Ministers of the Americas adopted a goal of regional eradication of polio from the Western Hemisphere by 1990. The subsequent implementation of polio-eradication strategies (focusing on routine vaccination with OPV, mass vaccination of all children aged 0-4 years through annual National Immunization Days {NIDs}, effective surveillance, and response to cases) resulted in a dramatic reduction in importations of polio. The last case of paralysis caused by indigenously acquired wild poliovirus in the Americas had onset in August 1991, and in 1994, the hemisphere was certified free of polio by an independent commission.

Other industrialized countries have had experiences similar to those of the United States. Most western European countries have been free of epidemic or endemic polio for many years, although limited outbreaks occurred in Finland in 1984-1985 and in the Netherlands in 1992-1993. Asia and Africa have been the areas most affected by polio in recent years.

In 1988, the World Health Assembly adopted a goal of global eradication of polio by 2000, and eradication efforts began throughout the world, largely using the strategies developed in the Americas. Under World Health Organization (WHO) leadership, a remarkable partnership of public and private organizations has been formed. Chief among these has been Rotary International, United Nations Children's Fund (UNICEF), and CDC. Additional financial support has been provided by the governments of Australia, Canada, Denmark, Italy, Japan, Norway, Sweden, the United Kingdom, and the United States. In the private sector, most notable has been the extraordinary commitment of Rotary International, which is donating approximately $400 million to support the effort and is providing essential financial and physical support from local Rotarians, including volunteers for social mobilization, vaccination posts, and advocacy efforts. A global laboratory network has been developed by WHO to support the eradication effort.

Unprecedented public health efforts by many countries where polio is endemic have characterized the polio-eradication effort. In several countries (including Afghanistan, El Salvador, and Sudan), civil wars have been temporarily suspended to allow vaccination of children in both government- and rebel-controlled areas. Seventeen nations in the Middle East, the Caucasus, and Central Asia have cooperated in coordinating NIDs (Operation MECACAR). Probably the most spectacular accomplishment has been the administration of OPV to more than 257 million children aged less than 5 years in a single week in 1996 as a result of simultaneous efforts in Bhutan, China, India, Myanmar, Nepal, Pakistan, Thailand, and Vietnam.

The reported incidence of polio in India has declined dramatically. China, with approximately one fourth of the world's population, has not detected indigenous wild poliovirus since 1994. The only indigenous transmission of polio in 1997 in WHO's Western Pacific Region occurred in the area of the Mekong delta. In the face of financial and societal crises, 31 countries in Africa have conducted NIDs, and those that have not done so already are in the planning phases.

The remaining challenges in the fight against polio are 1) resources to fully implement eradication strategies (a shortfall of approximately $50 million per year in donor support still remains); 2) maintenance of the political will to see the program through to ultimate success; and 3) development of surveillance systems in many countries to assure that circulation of poliovirus (or its absence) can be detected.

The United States has much to be proud of in the fight against polio. The U.S. Congress has supported global polio-eradication efforts through both the Agency for International Development and CDC. In addition, the United States is, and will continue to be, one of the major beneficiaries of polio eradication. The polio-free status the United States has enjoyed since 1979 comes at a cost, both personal and financial. Each year in the United States, there are five to 10 cases of vaccine-associated polio, a personal and societal tragedy; this number should be reduced substantially as a result of the recently adopted sequential IPV-OPV schedule. An estimated $230 million also is spent each year to maintain the high levels of polio vaccine coverage. Once polio is eradicated from the planet, polio vaccination can be discontinued, and the respective resources can be devoted to other important global health problems. In 1987, the objective of eradication was underscored: "Global eradication of poliomyelitis is inevitable; the only question is whether we will accomplish it or pass on the needed action to our successors. We believe we should act now to leave the legacy of a poliomyelitis-free world for our children" (1). It now seems clear that this commitment will be fulfilled. 1997 Editorial Note by Alan R Hinman, MD, MPH, Senior Consultant for Public Health Programs, Task Force for Child Survival and Development, and former Director, Immunization Division, Center for Prevention Services, CDC.

Reference

1. Hinman AR, Foege WH, de Quadros CA, Patriarca PA, Orenstein WA, Brink EW. The case for global eradication of poliomyelitis. Bull WHO 1987;65:835-40.

   
   

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