Polysaccharide Vaccines and Immunity

Distribution of Pneumococcal Types Responsible for Bacteremic Infection in the United States During 1968-1973 

Pneumococcal type Number of isolates Percentage of isolates 

and 9L and 9N (Ref. 84), of which, type 9N is used in the vaccine (see Table V). The choice of these serotypes (6A, 19F, and 9N) was made because, of all the serotypes in each cross-reacting group, these occur more frequently in disease isolates. 

Meningococcal disease (purulent meningitis) commonly occurs in children, but is also observed in adults. Without antibiotic treatment, the mortality rate is high (85%), and, even with this treatment, cured patients can suffer serious and permanent neurological deficiencies.165 These facts, together with the emergence of antibiotic-resistant strains,8 prompted the rapid development of a commercial vaccine. This vaccine was developed almost simultaneously with the pneumococcal vaccine. 

In contrast to the pneumococcal vaccine, however, the composition of the meningococcal vaccine was greatly simplified, due to the fact that fewer polysaccharides were required. Based on their capsular polysaccharides, there are only eight different serogroups of N. meningitidis (A, B, C, 29e, W-135, X, Y, and Z), of which, groups A, B, and 

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