This invention discloses compositions and methods of: vaccinating a subject; enhancing the vaccination efficiency; preparing a subject prior to vaccination response; and improving the clinical outcome after infectious challenge in a subject that has been vaccinated. More specifically, the invention pertains to delivering into a tissue of the subject a nucleic acid expression construct that encodes a growth-hormone-releasing-hormone ("GHRH") before or concomitantly with delivering a vaccine to the subject, wherein, GHRH is expressed in vivo in the subject, wherein the subject comprises a human, pig, cow, bird, horse or any other animal species receiving a vaccine.