Decline in Haemophilus influenzae Type b Meningitis --
Seattle-King County, Washington, 1984-1989
The first vaccines licensed in the United States for prevention
of Haemophilus influenzae type b (Hib) disease were composed of
the capsular polysaccharide of Hib, polyribosylribitol phosphate
(PRP). The vaccines, licensed in 1985, were moderately effective
in preventing Hib disease in children aged 24-59 months (1). In
December 1987, the first Hib conjugate vaccine was licensed. The
vaccine was recommended for use in children aged 18-59 months to
prevent meningitis and other forms of invasive disease caused by
Hib. This report summarizes surveillance for Hib meningitis and
provides data on the use of Hib vaccine in Seattle-King County,
Washington, where Hib meningitis surveillance methods have
remained the same since 1984.
In 1989, active surveillance and passive reporting identified
10 cases of culture-confirmed Hib meningitis in children aged
less than or equal to 83 months in Seattle-King County. These 10
cases represented a 73% decline from the annual average of 37
cases for 1984-1988 (Table 1). Moreover, since December 1987, the
number and proportion of reported cases among children aged 24-83
months has declined: in 1988, children in this age group
accounted for 6% of all cases reported; in 1989, 0; and in 1990
(through October), 5%. In comparison, from 1984-1987, this age
group accounted for an annual average of 21% of all cases (p=0.1,
p less than 0.04, and p less than 0.03, respectively).
From 1986 through 1989, approximately 18% of the children with
Hib meningitis had been immunized with PRP vaccine several weeks
to months before disease onset; one child had been immunized with
Hib conjugate vaccine 2 days before disease onset.
From 1987 through 1989, use of Hib vaccines increased
substantially in Seattle-King County: in 1989, the health
department administered 4675 doses, a fourfold increase over the
1114 doses administered in 1987. Community use was also
substantial in 1988: at least 27,725 doses of Hib conjugate
vaccine were ordered by
the private health-care community that year. Approximately 20,000
children reached the eligible age (i.e., 18 months) for conjugate
vaccine each year.
Reported by: J Boase, R Alexander, Seattle-King County Dept of
Public Health, Washington. Meningitis and Special Pathogens Br,
Div of Bacterial Diseases, Center for Infectious Diseases, CDC.
Editorial Note
Editorial Note: Several factors may have contributed to the
extensive use of Hib conjugate vaccine in Seattle. Hib vaccine
use has been supported by public- and private-sector health-care
providers. The Washington Department of Health has provided Hib
vaccines at no cost to county health departments and to private
providers. In addition, Hib vaccine is included on the health
department's computerized vaccination reminder system.
The findings in this report suggest that Hib vaccination
programs are effective in preventing Hib meningitis. Because the
incidence of Hib meningitis varies by year (2), comparisons
between years were based on the proportion of cases occurring in
different age groups during 1984-1987 and proportions for 1988,
1989, and 1990. Statistical differences in these proportions
occurred only among children aged 24-83 months (the group for
which the Hib conjugate and polysaccharide vaccines are
recommended) during a time when vaccine use had increased
substantially. The single case in a child immunized with the Hib
Conjugate Vaccine occurred before a protective immunologic
response could be expected (i.e., 10-14 days after vaccination)
and therefore does not represent a vaccine failure.
In general, substantial reductions in Hib disease rates have
not been documented in children in age groups for which the Hib
conjugate vaccines were licensed, possibly because of low vaccine
coverage rates. Recent licensure of Hib conjugate vaccines for
use in infants beginning at 2 months of age to be given
concomitantly with diphtheria and tetanus toxoids and pertussis
vaccine may help to increase coverage (3,4). Use of the conjugate
vaccines in infants should substantially reduce rates of Hib
disease since most Hib infections occur in children aged 2-18
months. This report suggests that an aggressive approach to
immunization by public health organizations and private
health-care providers may increase coverage and prevent disease.
References
Ward JI, Broome CV, Harrison LH, Shinefield H, Black S.
Haemophilus influenzae type b vaccines: lessons for the future.
Pediatrics 1988;81:886-93.
Sherry B, Emanuel I, Kronmal RA, et al. Interannual variation
of the incidence of Haemophilus influenzae type b meningitis.
JAMA 1989;261:1924-9.
CDC. Food and Drug Administration approval of use of
Haemophilus b Conjugate Vaccine for infants. MMWR 1990;39:698-9.
CDC. Food and Drug Administration approval of use of a
Haemophilus b Conjugate Vaccine for infants. MMWR 1990;39:925-6.
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