Polysaccharide-protein conjugate vaccines are members of a new class of vaccines designed to immunize infants against diseases caused by encapsulated bacteria, including H influenzae type b. There are at least four H influenzae type b polysaccharide-protein conjugate vaccines undergoing clinical evaluation in the United States,1 and three of the four recently were licensed for use in 18-month-old children. Although these conjugate vaccines differ considerably in chemical composition and immunologic properties, each consists of the H influenzae type b polysaccharide, polyribosylribitolphosphate (PRP) (or a derivative thereof), covalently coupled to a carrier protein or proteincontaining complex. As a group, the H influenzae type b polysaccharide-protein conjugate vaccines are more immunogenic in healthy infants and older children than the conventional PRP vaccine.1,2 Several groups of children have been found to be at increased risk for invasive disease caused by H influenzae type b compared with children in the general US population. These include Native Americans (Apaches, Navajos, and Alaskans),3-6 blacks (when studied with regard to allotype),7-9 and children with previous disease caused by H influenzae type b.10,11 Other groups of children who have underlying diseases or genetic phenotypes associated with impaired serum antibody responses to immunization with conventional PRP vaccine have been described (Table 1). In most instances, children without these conditions also are considered to be at a higher risk of invasive disease caused by H influenzae type b than children of comparable ages in the general population.3-6,22,24-26 The reasons for the poor antibody responses to PRP vaccine in children with these underlying conditions, in children of certain racial groups, or in children with hyporesponsive genetic phenotypes are not well understood.
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Weinberg et al. (1990) studied this question.