ATLANTA Haemophilus influenzae type b (Hib) conjugate vaccines are making progress toward the elimination of invasive Hib disease, according to a recent report by the Centers for Disease Control and Prevention.
Before the vaccine was introduced in 1987, Hib was the most common cause of bacterial meningitis among children in the United States. Meningitis was a leading cause of acquired mental retardation in the United States and left many children blind, deaf or paralyzed, according to Centers for Disease Control and Prevention statistics from the 1980s.
Of those U.S. children who contracted Hib before 1987, an estimated one in 200 children younger than age 5 developed invasive Hib disease.
Between 1987 and 1994, the incidence of invasive Hib disease declined 95% among children younger than age 5 because of the vaccine. Between 1987 and 1995, the incidence of all invasive H. influenzae diseases among children under 5 declined 96%, the report stated.
Identification of the serotype of cases of invasive H. influenzae disease is essential for evaluating changes in the epidemiology of Hib disease. In the United States, the percentage of invasive Hib disease cases among children with serotype information has increased substantially; from 41% of 340 cases in 1994, to 63% of 317 cases in 1995. These data suggest the proportion of H. influenzae cases caused by Hib has been decreasing, according to the CDC report.
Although widespread vaccination with conjugate vaccine has reduced Hib colonization rates among young children, circulation of the organism continues. Population groups with low levels of vaccination probably contribute, the report stated, to the ongoing occurrence of disease and regional differences in disease incidence.
Because conjugate vaccines reduce Hib carriage and interrupt transmission of the organism, complete coverage among preschool-age children will help eliminate disease among infants who are too young to be completely vaccinated.
To monitor progress toward meeting the goal of eliminating invasive Hib disease among children younger than 5, and to evaluate changes in the epidemiology of invasive Hib disease, the report suggests national surveillance for Hib be expanded to include four elements:
Because Hib vaccines protect against the H. influenzae serotype b organism only, serotyping should be performed for all cases of invasive Hib disease; to improve characterization of groups at risk for undervaccination and Hib disease, vaccination status of all children with invasive Hib disease should be assessed; to ensure continued high levels of vaccine effectiveness and to enable systematic evaluation of factors associated with vaccine failure in those with Hib disease, the date, vaccine manufacturer and vaccine lot number should be included in the case report; important indicators of the severity of Hib infections should be reported, including the type of clinical syndrome, specimen source and clinical outcome.
The report summarized data about trends in invasive Hib disease during 1987-1995 from three separate surveillance systems. The findings of this study underscore the need for age-appropriate vaccination of infants and for complete investigation and reporting of cases of invasive Hib disease.
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