are not reported. Nevertheless, as morbidity and mortality from pertussis have declined, these reactions have drawn considerable attention. The frequency of fatal reactions has been estimated to be 1 to 2 cases per 10 million injections, and the frequency of serious neurologic disorders such as encephalopathy to be 1 case per 110,000 infections, with persistent neurological dysfunction one year later at 1 case/310,000 infections (Cody et al., 1981; Miller et al., 1981). The rate of adverse reactions is considered by all to be higher than desirable, and by a few to be unacceptable (Fulginiti, 1984).
Several serotypes of Bordetella pertussis have been defined, but there are no definitive data indicating that protection is serotype-specific. The development of improved pertussis vaccines has been hindered in the past by incomplete understanding of the pathogenesis of the disease, by the lack of a suitable animal model, and by uncertainty surrounding the pathogenic roles played by several exotoxins and cell wall components of the pertussis organism. Considerable progress has been made recently in characterizing some of these products, including pertussis toxin, lymphocytosis promoting factor, filamentous hemagglutinin (FHA), adenylate cyclase, lipopolysaccharide (LPS), dermonecrotic toxin, and the various agglutinogens that define the “serotype” of B. pertussis (Robbins, 1984). However, the roles played by these components and the potential benefits of antibodies manufactured against them remain unclear.
It has not been possible to define the host immune response to B. pertussis in contemporary immunologic terms, because so little is known about the antigens that induce protection. Studies reported by the British Medical Research Council in the 1950s showed good correlation between standard potency (mouse protection) test results and clinical protection (Medical Research Council, 1956). Based on these results and those of other studies, the mouse potency test was selected as an indication of efficacy in lieu of immunologic data or field studies (Robbins, 1984).
Agglutination titers of the sera of those vaccinated in the British studies also were found to correlate well with efficacy. Agglutination titers of 1:320 or better were associated with protection. One notable exception was observed with a partially purified soluble antigen, the first soluble antigen pertussis vaccine ever used. This vaccine was highly effective in terms of clinical protection, but did not result in an agglutinin response except to the specific serologic strain that was used in production of the soluble antigen. In other studies, protection has been found in the presence of low agglutination titers. Hence, it is unclear whether the absence of agglutinins predicts susceptibility.