Acceptance of the “second infection” hypothesis as a valid explanation of the pathogenesis of DHF and DSS has obvious implications for the problem of immunization against dengue fever. The question is whether possession of crossreactive antibodies resulting from vaccination may, at least in some individuals, predispose to aggravated illness upon subsequent infection. The notion that such antibodies are not necessarily protective is supported by field and experimental observations going back to Siler et al. (1926) and Simmons et al. (1931). In more specific terms, Sabin’s (1952a) experiments in adult human volunteers with types 1 and 2 showed that cross protection was effective for only about 2 months, then waned until after 9 months heterologous reinfection produced definite, though still modified, illness. The case described by Carey et al. (1965) in which two episodes of disease, one caused by type 4, the other by type 1, occurred 1 year apart in the same individual, has already been discussed.
KeywordsDengue Virus Dengue Fever Yellow Fever Japanese Encephalitis Japanese Encephalitis Virus
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