On the basis of the incidence in the prevaccine era (Ward and Cochi, 1988) for the 24- to 35-month age group (presumably, the main age group previously immunized with PRP vaccine) of 1.0 per 100,000 per week (i.e., the annual rate divided by 52) and the Mantel-Haenszel odds ratio for the metaanalysis of 2.62, the attributable incidence is 2.62 - 1.0 = 1.62 cases of early-onset (within 7 days of vaccination) Hib disease per 100,000 vaccinees. It should be stated, however, that the above figures may not be valid, since today the 7-day incidence of disease is probably less than the 1.0 per 100,000 from the prevaccine era owing to decreased colonization and transmission of disease.

The evidence favors rejection of a causal relation between immunization with Hib conjugate vaccines and early-onset Hib disease.

The evidence is inadequate to accept or reject a causal relation between PRP vaccine and early-onset disease in individuals who previously received one or more doses of Hib conjugate vaccine.

Risk-Modifying Factors

Because immunization with Hib vaccines may lead to a transient decrease in protective antibody levels, unimmunized children at increased risk of colonization (household or day-care contact with individuals with recent cases of Hib infection) may require special measures (see the recommendations of the American Academy of Pediatrics, Committee on Infectious Diseases [1991a]). A number of studies have demonstrated the safety and efficacy of Hib conjugate vaccines in high-risk groups such as adults with human immunodeficiency virus infection (Steinhoff et al., 1991) and children with sickle cell anemia (Frank et al., 1988; Rubin et al., 1992), cancer (Feldman et al., 1990), and asplenia (Jakacki et al., 1990), although in the latter two groups the antibody responses to vaccine were lower than normal.

ANAPHYLAXIS

Clinical Description

Anaphylaxis and anaphylactic shock refer to an acute, severe, and potentially lethal systemic allergic reaction. Signs and symptoms begin within minutes to a few hours after exposure. Death, if it occurs, usually results from airway obstruction caused by laryngeal edema or bronchospasm and may be associated with cardiovascular collapse. Most cases resolve without sequelae, and early treatment with alpha-adrenergic drugs can abort the full expression of the syndrome. A general discussion of anaphylaxis can be found in Chapter 4.



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