Abstract
Summary and Conclusions
The spotted fever group complement fixing antibody response was used as a measure of the immunogenicity of a commercially available killed Rocky Mountain spotted fever vaccine in human subjects. A single-dose primary course of vaccine elicited a detectable antibody response in only about 22% of 68 subjects, whereas a 3-dose primary course stimulated the development of complement fixing antibodies in about 63% of eight subjects. The low antibody titers attained may be a function of the relatively low complement fixing antigen content of the vaccine.
A booster dose of vaccine given between 1 and 6 months after the primary course failed to elicit an antibody response in the majority of subjects. A second booster dose, given a year after the 6-month booster dose, also failed to cause a significant response. On the other hand, three subjects who had last received RMSF vaccine several years prior to this study developed a typical secondary antibody response upon revaccination. These same subjects, however, failed to show an antibody response to an additional dose of vaccine 6 months later.
The interval between doses or courses of the currently available vaccine required for eliciting an optimal secondary CF antibody response is unknown, but the results of this study suggest that it may be greater than one year.
It is unknown if the uniformly low CF antibody response in man to the commercial RMSF vaccine reflects an equally low degree of protection afforded against the disease. Minimum requirements for potency of RMSF vaccine lots released for distribution include demonstration of capacity to protect guinea pigs against challenge with virulent organisms (5). Studies of the protective effect of the vaccine in man would seem desirable to evaluate its efficacy and to establish the degree of correlation of protection with laboratory tests.
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