The Principal Investigator proposes to construct a hybrid polio/dengue genome in order to develop a vaccine for dengue virus. The dengue gene fragments will replace a segment of the polio virus envelope genes. Cell lines that supply the capsid proteins but lack the non-structural proteins genes may be used to encapsulate the polio/dengue genomes. Such hybrid genomes would be defective and, thus incapable of forming infectious virus particles following immunization. The investigator anticipates that such chimerae will effectively present dengue envelope protein and induce effective immunologic responses against the virus. Further, chimerae will be constructed in Phase II and their ability to induce neutralizing antibodies and protect mice from infection will be evaluated.