The invention describes the development of more potent peptide vaccines to prevent or treat infections or cancer. Small synthetic peptides from the known sequences of viral, bacterial, parasitic or tumor antigens are modified so they can spontaneously form complexes with a synthetic nucleic acid, such as Poly IC, that functions as an immunological adjuvant. The peptide-nucleic acid complexes are dramatically more immunogenic as compared to the separate components. The procedure for developing the vaccine involves the conjugation of a synthetic peptide containing a C residue to poly-K using a bi-functional cross-linking reagent (SMCC). The peptide/poly-K complex was then formulated with CMC and poly-IC to produce a self-adjuvant vaccine that was 36-fold more effective as compared to the same peptide administered mixed with the same adjuvant (but not complexed to it).