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Current Trends Poliomyelitis -- United States, 1975-1984

In September 1985, CDC-selected consultants individually reviewed clinical, laboratory, and epidemiologic data on 150 suspected cases of poliomyelitis reported to CDC from 1975-1984. CDC's Division of Immunization, Center for Prevention Services, and Division of Virology, Center for Infectious Diseases, had tentatively determined that 121 cases met the case definition for paralytic poliomyelitis.* Overall, 118 cases were accepted by the consultants as cases and classified according to an epidemiologic classification system established in 1975 that provides "epidemic," "endemic," "imported," and "immune-deficient" categories (Table 1).

Compared to the average of 15,822 cases per year during 1951-1955, the period directly preceding the widespread availability and use of polio vaccines, U.S. cases averaged 15 per year during 1975-1979 and declined to nine per year during 1980-1984. Of the total 118 cases for 1975-1984, 10 (8%) were epidemic cases, i.e., were epidemiologically linked with another case(s), all from a 1979 epidemic caused by a wild type 1 poliovirus; 12 (10%) were imported cases among U.S. citizens with illness onset before or after return to the United States; and 11 (9%) were cases occurring among persons with primary immunodeficiencies. One of these latter cases, which occurred in 1981 in a nontraveler, was the last case of endemic, wild-virus poliomyelitis in the United States. The remaining 85 (72%) cases were endemic, i.e., were not epidemiologically linked to another case(s); 71 (60%) were epidemiologically associated with vaccine usage. Of the 71 vaccine-associated cases, 30 (42%) occurred among vaccine recipients, and 41 (58%), among contacts of vaccine recipients. Fourteen (40%) of the endemic cases were not epidemiologically associated with vaccine; however, five had virus isolates characterized definitively as vaccine-related. Reported by Surveillance, Investigations, and Research Br, Div of Immunization, Center for Prevention Svcs, Div of Viral Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Continuing transmission of wild virus-caused paralytic poliomyelitis has been eliminated in the United States using the currently recommended immunization policy of the Immunization Practices Advisory Committee (ACIP), which relies primarily on oral polio vaccine (OPV) use for the primary immunization series (1). From 1980 to 1984, only three of 45 cases (two imported and one immune-deficient) were documented as wild by strain characterization of poliovirus isolates. A third imported case was presumed epidemiologically to be caused by a wild poliovirus. Otherwise, the rare cases of reported paralytic poliomyelitis in the United States have been vaccine-associated.

The risk of vaccine-associated paralytic poliomyelitis, based on 85 cases occurring in immunologically normal recipients and contacts and the distribution of an estimated 274.1 million doses of OPV during 1973-1984, is one case per 3.22 million doses of OPV distributed.

When all 104 vaccine-associated cases (85 among immunologically normal recipients and contacts; 13 among immune-deficient recipients and contacts; and six others, patients from whom a vaccine-like virus was isolated) from this same period are included, the overall vaccine-associated risk is one case per 2.64 million doses of OPV distributed.

At the October 24-25, 1985, meeting of the ACIP, issues concerning polio vaccines and current polio vaccination policy in the United States were reviewed. Discussion included live polio vaccine and both the currently available inactivated polio vaccine (IPV) and a more potent IPV not currently available in the United States. The issues discussed included seroconversion, intestinal immunity, duration of immunity, replication of poliovirus in the intestine, safety, immunization coverage, seroprevalence, the current epidemiology of poliomyelitis in the United States, and the estimated likelihood of wild poliovirus introduction. In light of the data reviewed, the ACIP concluded that no change in the basic U.S. approach to poliomyelitis (primary reliance on OPV with selected use of IPV (1)) is warranted currently but that the subject should be reviewed on a continuing basis.

Reference

  1. ACIP. Poliomyelitis prevention. MMWR 1982;31:22-6, 31-4. *Since 1969, the CDC definition of a case of paralytic poliomyelitis has been a patient with paralysis clinically and epidemiologically compatible with poliomyelitis who, at 60 days after onset of symptoms, has a residual neurologic deficit, has died, or for whom no information is available on neurologic residua.



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