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Declining incidence of Haemophilus influenzae type b disease since introduction of vaccination
T V Murphy1, K E White, P Pastor
1Department of Pediatrics, University of Texas Southwestern Medical Center, Dallas 75235-9063.
Insights
Vaccination significantly reduced invasive Haemophilus influenzae type b disease in children. The conjugate vaccine, introduced in 1988, showed substantial incidence declines, even in unvaccinated infants.
Area of Science:
- Pediatric Infectious Diseases
- Vaccinology
- Epidemiology
Background:
- Haemophilus influenzae type b (Hib) disease historically posed a significant threat to young children.
- The introduction of polysaccharide and conjugate vaccines aimed to reduce the burden of Hib infections.
Purpose of the Study:
- To assess the incidence of invasive Hib disease in Minnesota and Dallas County before and after vaccine introduction.
- To evaluate the impact of plain polysaccharide and conjugate vaccines on Hib disease rates in children.
Main Methods:
- Active, laboratory-based surveillance identified culture-proven cases of invasive Hib disease.
- Incidence was calculated per 100,000 child-years, comparing baseline (1983-1984) to post-vaccination periods (through 1991).
- Study included children under 5 years old in Minnesota and Dallas County, Texas.
Main Results:
- Invasive Hib disease incidence decreased by 85% in Minnesota and 92% in Dallas County between the baseline and 1991.
- Significant declines were observed in both vaccinated age groups and unvaccinated infants younger than 18 months.
- A total of 2557 confirmed cases were analyzed from 1983 to 1991.
Conclusions:
- Vaccination strategies have led to a profound reduction in invasive Hib disease in the studied US regions.
- The findings suggest that Hib vaccines not only protect vaccinated individuals but also reduce disease transmission to unvaccinated populations.
- The data support the effectiveness of conjugate vaccines in controlling Hib infections.
Objective:
To determine the incidence of invasive Haemophilus influenzae type b disease in children living in Minnesota and Dallas County, Texas, before and since introduction of plain polysaccharide vaccine in 1985, and conjugate vaccine in 1988. Initially, use of these vaccines was limited to infants 18 months of age and older.
Design:
Identification of culture-proven cases of H influenzae type b disease was through systems of active, laboratory-based surveillance. The mean incidence of disease (cases observed/100,000 child-years) for 1983 and 1984 served as a baseline for comparison with subsequent years through 1991.
Participants:
Children less than 5 years of age in Minnesota and Dallas County, Texas. Overall, there were 2557 confirmed age-eligible cases of invasive H influenzae type b disease from 1983 through 1991.
Results:
Between the 1983-1984 baseline and 1991, the incidence of H influenzae type b disease decreased 85% in Minnesota and 92% in Dallas. Notably, declines in incidence were observed in children in the age group being vaccinated as well as in infants younger than 18 months of age prior to introduction of vaccination.
Conclusion:
In two widely separated areas of the United States, a profound decrease in the incidence of H influenzae type b disease has occurred. The data suggest that vaccination may be protecting against disease, as well as decreasing the spread of infection to unvaccinated infants.