Current Trends Progress Toward Eradicating Poliomyelitis from the Americas

The World Health Organization (WHO) estimates that greater than 250,000 cases of paralytic poliomyelitis occur each year worldwide (WHO, unpublished data, 1986). The introduction and widespread use of inactivated poliovirus vaccine (IPV) in 1955 and live, attenuated oral poliovirus vaccine (OPV) in 1961 dramatically affected the reported incidence of poliomyelitis in the United States and other developed countries (1).

During the early 1980s, intensive, biannual national vaccination campaigns substantially reduced the number of polio cases in Brazil (2). In addition, from 1975 to 1984, the number of countries in the Western Hemisphere reporting cases decreased from 19 to 11. These successes led the Pan American Health Organization (PAHO) in 1985 to establish a goal of and a plan for eradication of the indigenous transmission of wild polioviruses from the Americas by the end of 1990. A major objective of the plan was to establish regional and national surveillance systems so that 1) all cases of acute flaccid paralysis could be rapidly investigated to determine whether they were polio-related and 2) control measures to stop transmission could be rapidly implemented after the report of a suspected case of polio. A second major objective was to increase vaccination levels with three doses of OPV to at least 80% in children by 1 year of age in each country of the region by 1990.

Progress has been made since the goal was announced, particularly since April 1987, when the plan received formal funding. The intensification of surveillance activities since 1986 resulted in a 77% increase in notification of acute flaccid paralysis regionwide in 1988 over that in 1985 (Table 1). Despite this increase, the incidence of confirmed* polio reported in the region has declined. In 1988, 335 confirmed cases were reported in the Americas (Table 1), representing a 64% decline from 1986 (930 cases) and a 49% decline from 1987 (652 cases). In addition, the stable, low level of polio activity in the region during 1988, as well as the absence of large outbreaks (Figure

1. (such as occurred in Brazil in 1986), suggest that transmission of polio has been substantially suppressed. In 1989, as of July 22, 66 confirmed cases of polio have been reported, representing a 71% decrease from the 224 cases reported during the same period in 1988.

Since 1987, the laboratory network for characterizing polioviruses isolated from stool specimens obtained from persons with suspected polio has been greatly strengthened. Preliminary laboratory data for 1988 indicate that 32** wild polioviruses were isolated from patients in five countries, compared with 43 isolates from patients in six countries in 1987.

The decrease in the proportion of "municipios" (counties or districts) with confirmed polio cases in the region during 1985-1988 also indicates substantial progress (Table 2). Only 1.9% of the nearly 14,400 municipios reported confirmed polio cases in 1988, suggesting that circulation of wild poliovirus is focal and confined to a small proportion of geopolitical units.

Regionwide data on polio vaccination levels, which have been available since 1978, should be interpreted with caution because of changes over time in the methodology for assessing coverage, in the personnel assessing the data, and in the population estimates used as denominators in the calculations. Regionwide OPV coverage of children by 1 year of age based on three doses of vaccine was estimated at 82% in 1988. However, four countries (Brazil, Cuba, Mexico, and Paraguay), constituting 56% of the total annual birth cohort in the region, rely primarily on biannual national vaccination campaigns for routine vaccination of infants and report OPV coverage based on two doses of vaccine. A separate analysis was done that comprises only the 35 countries that report data based on three doses of vaccine (Figure 2). A steady increase in OPV coverage based on three doses occurred during 1980-1988 in these countries, reaching an all-time high of 71% in 1988. Nonetheless, the goal of achieving vaccination levels of at least 80% in these countries by 1990 will be difficult to achieve. Special vaccination efforts, including house-to-house vaccination, are under way in several countries to attempt to achieve this goal. Reported by: Expanded Programme on Immunization, Pan American Health Organization, Washington, DC. International Health Program Office; Respiratory and Enterovirus Br, Div of Viral Diseases, Center for Infectious Diseases; Surveillance, Investigations, and Research Br, Div of Immunization, Center for Prevention Svcs, CDC.

Editorial Note

Editorial Note: The eradication of smallpox in 1977 suggested the potential for eradication of other infectious diseases. In 1985, PAHO embarked on an initiative to eradicate the indigenous transmission of wild polioviruses in the Western Hemisphere by 1990. Reported polio in the region declined by 64% during 1986-1988; a record low of 335 confirmed cases was reported in 1988. The circulation of wild poliovirus is probably focal within the region. Polio surveillance systems are functioning well in all countries of the region. Despite improvement in capability of isolating wild polioviruses since 1987, the decrease in the number of wild virus isolates provides additional evidence of progress in interrupting circulation of wild poliovirus in the region. If the current level of effort is sustained and special efforts are directed toward the remaining foci of infection, eradication of polio from the Americas probably can be achieved.

Even though progress toward polio elimination has been substantial, indigenous polio transmission may continue in at least one country after 1990. Those countries at highest risk include Brazil, Colombia, Guatemala, Haiti, Mexico, and Peru. Technical and operational problems must still be addressed and overcome if the initiative is to succeed.

Financial support is crucial to the success of the project. In addition to ongoing support by the governments of the member states of PAHO, several donor agencies have contributed to a grant totaling $47.6 million for 1987-1991 (U.S. Agency for International Development ($20.6 million), Rotary International ($10.7 million), Inter-American Development Bank ($6.6 million), United Nations Children's Fund ($5.0 million), and PAHO/WHO ($4.7 million)). Overall project direction and management have been provided by PAHO's Expanded Programme on Immunization office.

The prospect of polio eradication in the Americas led the 41st World Health Assembly of WHO to adopt a resolution in May 1988 to eradicate poliomyelitis from the world by the year 2000 (4). The U.S. government is committed to providing technical and financial assistance for the eradication effort.

Global eradication of poliomyelitis can be accomplished by a strategy that includes achievement and maintenance of high immunization levels, effective surveillance to detect all new cases, and a rapid vigorous response to the occurrence of new cases (5). International collaboration will be necessary to achieve this goal. Operational obstacles must be overcome to ensure vaccination of all persons, and research efforts must be directed at improving vaccination schedules and/or formulations of existing vaccines. Eradication of polio in the Americas is an essential first step in the strategy toward global eradication. References

1. Kim-Farley RJ, Bart KJ, Schonberger LB, et al. Poliomyelitis in the USA: virtual elimination of disease caused by wild virus. Lancet 1984;2:1315-7.

2. Risi JB Jr. The control of poliomyelitis in Brazil. Rev Infect Dis 1984;6(suppl 2):S400-3.

3. Health and Welfare Canada. A case of paralytic poliomyelitis--Ontario. Canada Dis Weekly Rep 1988;14:229-30.

4. World Health Assembly. Global eradication of poliomyelitis by the year 2000. Geneva: World Health Organization, 1988. (Resolution WHA41.28).

5. 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. *The following case definitions for paralytic poliomyelitis have been implemented by PAHO: A suspected case is any acute onset of paralysis in a person less than 15 years of age for any reason other than severe trauma, or paralytic illness in a person of any age in which polio is suspected. The classification of a suspected case is temporary; within 48 hours of notification, the case should be reclassified as "probable" or "discarded." A probable case is a suspected case with acute flaccid paralysis and no other cause that can be immediately identified. The classification of a probable case is also temporary, and within 10 weeks of its onset the case should be reclassi fied as "confirmed" or "discarded." A probable case is classified as confirmed if there is: 1) laboratory confirmation (wild virus grown from stool or a greater than or equal to 4-fold rise in poliovirus neutralization antibody titer between acute and convalescent serum specimens); 2) epidemiologic linkage to a probable or confirmed case; 3) residual paralysis 60 days after onset; 4) death; or 5) lack of follow-up of the case. **Does not include a wild poliovirus type 1 isolate from a patient in Canada (3).

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