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
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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