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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

  1. Ward JI, Broome CV, Harrison LH, Shinefield H, Black S. Haemophilus influenzae type b vaccines: lessons for the future. Pediatrics 1988;81:886-93.

  2. Sherry B, Emanuel I, Kronmal RA, et al. Interannual variation of the incidence of Haemophilus influenzae type b meningitis. JAMA 1989;261:1924-9.

  3. CDC. Food and Drug Administration approval of use of Haemophilus b Conjugate Vaccine for infants. MMWR 1990;39:698-9.

  4. 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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