Synthetic recombinant vaccines are expression vectors incorporating defined epitope(s) of microbial agents. They are prepared by inserting synthetic oligonucleotide(s) coding for previously identified relevant epitopes into the genome of a desired vector, using recombinant DNA technology. The results discussed indicate that immunization with such vaccines carrying viral epitopes may lead to protective immunity against viral agents. Oligonucleotides coding for three influenza epitopes stimulating B cells, T helper cells and cytotoxic lymphocytes were individually inserted into the flagellin gene of a Salmonella vaccine strain. Immunization of mice with the resultant recombinant bacteria or their isolated flagella induced a specific mucosal anti-influenza protective response. The most efficient vaccine consisted of all three recombinant flagella, administered intranasally. The protection elicited was cross-strain specific, long-lasting and efficient against a lethal viral challenge.