The Hib vaccines themselves contain no infective agents, just the organism's capsular polysaccharide; thus, there is no risk of developing Hib infection or clinical manifestations of Hib disease from any of the Hib vaccine components themselves (Granoff and Osterholm, 1987; Weinberg and Granoff, 1988). Occasionally, however, Hib disease is falsely diagnosed following immunization with both plain PRP and conjugated Hib vaccines, on the basis of the results of urine PRP antigen detection tests, because children excrete PRP in their urine for several days following immunization (Goepp et al., 1992; Jones et al., 1991; Spinola et al., 1986). The risk of developing a Hib infection within the first 7 days following immunization with Hib vaccines is discussed later in this chapter.

Rates of local reactions to Hib vaccines, such as pain, tenderness, swelling, and erythema at the site of injection, have varied from study to study, but the overall reaction rates to plain PRP vaccines are lower than those to conjugate vaccines. Approximately 20 to 25 percent of children develop local pain or tenderness, and 5 to 15 percent have redness or swelling at the injection sites in the 24 to 72 hours following immunization. These reactions are almost always mild and transient. Low-grade fever has been reported in the first 24 to 72 hours postimmunization in from 1 to 20 percent of Hib vaccine recipients. Temperatures of 39ºC (102.2ºF) or greater have been reported in less than 2 percent of Hib vaccine recipients. Most investigators have reported irritability in 10 percent or fewer of plain PRP vaccine recipients and about 10 to 25 percent of conjugate vaccine recipients. These systemic reactions are short-lived and are not felt to be serious by parents or physicians (Ahonkhai et al., 1990, 1991; Barkin et al., 1987; Black et al., 1987, 1991b; Campbell et al., 1990; Claesson et al., 1988, 1989, 1991; Clements et al., 1990; Dashefsky et al., 1990; Decker et al., 1992; Eskola et al., 1990a; Ferreccio et al., 1991; Frayha et al., 1991; Fritzell and Plotkin, 1992; Granoff and Cates, 1985; Granoff and Osterholm, 1987; Greenberg et al., 1987; Hendley et al., 1987; Kayhty et al., 1988, 1989; Kovel et al., 1992; Lenoir et al., 1987; Lepow et al., 1984a, 1985, 1986, 1987; Milstien et al., 1987; Parke et al., 1991; Peltola et al., 1977; Popejoy et al., 1989; Rowe et al., 1990; Santosham et al., 1991a; Vadheim et al., 1990; Watemberg et al., 1991; Weinberg and Granoff, 1988).

Rates of local and systemic reactions to Hib vaccines have usually been similar to or lower than those to injections with placebo or DPT, inactivated polio vaccine, or measles-mumps-rubella vaccine (MMR) alone or to those vaccines plus Hib vaccines (Ahonkhai et al., 1991; Black et al., 1991b; Campbell et al., 1990; Clements et al., 1990; Eskola et al., 1987; Lepow et al., 1984a, 1987; Vadheim et al., 1990; Watemberg et al., 1991). Exceptions include a study by Dashefsky et al. (1990), in which 71 percent of

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