The present invention relates to the use of the pituitary adenylate cyclase activating peptide (PACAP) as a molecular adjuvant for vaccines. Among other applications, these vaccines may be used in the protection against infectious agents such as viruses, bacteria and ectoparasites affecting mammals, birds and aquatic organisms. The PACAP, combined with a particular antigen, demonstrates its effectiveness as adjuvant increasing the host immune response against that antigen. This type of response can be observed when the vaccine compositions or combinations that include PACAP are administered orally, by injection, or by immersion baths, in case of aquatic organisms.
