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Rationale
For Prevention of Hepatitis A
Through Routine Active Immunization
The overall incidence of hepatitis A has declined in the United
States over the past several decades primarily as a result of
better hygienic and sanitary conditions (e.g., improved water
supplies, sewage disposal, and food sanitation and less crowded
living conditions). However, hepatitis A continues to be one
of the most frequently reported vaccine preventable diseases,
and the continued occurrence of extensive communitywide outbreaks
indicates that hepatitis A remains a major public health problem.
The availability of hepatitis A vaccine provides the opportunity
to substantially lower disease incidence and potentially eliminate
infection. The similarities between the epidemiology of hepatitis
A and poliomyelitis indicate that a reduction in disease incidence
can be achieved once persons in age groups that have the highest
rates of HAV infection and who serve as a reservoir of infection
are immunized (92). Producing a highly immune population reduces
the incidence of hepatitis A and decreases transmission by preventing
fecal shedding of HAV.
The goals of hepatitis A immunization are to a) protect persons
from infection; b) reduce disease incidence by preventing transmission;
and c) ultimately eliminate transmission (93). Because of their
high disease incidence and critical role in HAV transmission,
children should be a primary focus of immunization strategies.
Routine childhood vaccination would a) prevent infection in age
groups that account for at least one third of cases; b) eliminate
a major source of infection for other children and for some adults;
and c) eventually prevent infection in all older persons as vaccinated
children become adults, because immunity appears to be long-lasting.
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To achieve these goals, hepatitis A immunization strategies
have been developed and implemented incrementally, on the basis
of the characteristics of hepatitis A epidemiology and the feasibility
and effectiveness of hepatitis A vaccination. Initial recommendations
involved vaccination of persons in populations at increased risk
for hepatitis A and of children living in communities with the
highest rates of infection and disease. Vaccination of persons
in groups at increased risk for HAV infection (e.g., travelers)
or its adverse outcomes (e.g., persons with chronic liver disease)
will provide personal protection to these persons but will have
little effect on national disease rates, because most cases do
not occur among persons in these groups. Routine vaccination
of children living in communities with the highest rates of disease
(i.e., high rate communities) has been effective in interrupting
ongoing outbreaks and preventing subsequent outbreaks in these
communities (see Communities with High Rates of Hepatitis A on
page 9). Vaccination limited to these areas might have some impact
on overall disease incidence. However, only a small proportion
of nationally reported hepatitis A cases occur in these communities.
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To achieve a sustained reduction in national incidence of hepatitis
A, more widespread routine vaccination of children is needed.
Surveillance data have been used to identify states, counties,
and communities that have had consistently elevated rates of
hepatitis A and that contribute the majority of cases to the
current national disease burden. The 11 states in which the average
annual incidence of hepatitis A was ≥20
cases per 100,000 during 19871997, representing 22% of the
U.S. population, accounted for an average of 50% of reported
cases each year (Table 2). Reducing hepatitis A incidence in
these states, counties, and communities through sustained routine
vaccination of children should substantially reduce national
disease incidence. Assuming that a linear decline in hepatitis
A cases would occur during a 30-year period in which successive
cohorts of children living in areas with consistently elevated
rates are vaccinated, the direct medical costs per case prevented
would be expected to be of the same magnitude as those for other
recently recommended vaccines (94,95) (CDC, unpublished data,
1999).
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