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antibody in older children (Peltola et al., 1984). However, the committee believes the focus should be directed toward a vaccine that would be effective in younger children because of the distribution of the disease described below.

DISTRIBUTION OF DISEASE

Geographic Distribution

H. influenzae type b disease occurs worldwide. The pattern of disease in developing countries is similar to that in the United States with two exceptions. The first is that the disease occurs at a younger age: 40 to 50 percent of cases occur between 6 and 9 months of age. The second is that the mortality rate for H. influenzae type b meningitis can reach 40 percent even with treatment, in contrast to 5 percent for treated cases in the United States (Cadoz et al., 1983; Cochi, personal communication, 1983; Griffiss, personal communication, 1985; Hill, 1983; Norden, 1982). Also, about 30 to 40 percent of survivors exhibit neurological sequelae (Cadoz et al., 1983; Griffiss, personal communication, 1985).

Disease Burden Estimates

Very few studies are available on which to base estimates of the burden of disease from H. influenzae type b in developing countries. The most comprehensive reports appear to be those of Cadoz et al. (1981, 1983). These, however, are for a single location, Dakar, Senegal, and reflect a population with access to hospital care. The authors reported that H. influenzae meningitis was most frequent between 6 months and 2 years of age, rarely occurring before 2 months or after 5 years. Ninety-seven percent of cases were caused by type b. The incidence for infants and children under 5 years was 60 cases per 100,000 (Cadoz et al., 1983). This rate is slightly higher than that observed for typical U.S. populations, but lower than that reported for Navajo Indian and Alaskan Eskimo populations (Norden, 1982). For the disease burden calculation, the rate reported by Cadoz et al. (1983) is assumed to be reasonably representative of that in all developing countries. Fatality rates for H. influenzae type b meningitis are assumed to be 33 percent, and neurological sequelae are assumed to occur in 33 percent of survivors (Cadoz et al., 1983; Griffiss, personal communication, 1985).

Table D-3.1 shows the disease burden due to meningitis caused by H. influenzae type b. Sequelae are assumed to be distributed in severity in about the same proportion as those in the United States (Institute of Medicine, 1985).

The number of cases of nonmeningitic H. influenzae type b invasive disease can be estimated only by analogy with the situation in the United States. Various studies in the United States have reported that nonmeningitic conditions account for 30 to 80 percent of invasive illness caused by all types of H. influenzae (Institute of Medicine,



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