Multimeric hybrid genes encoding the corresponding chimeric protein comprise a gene sequence coding for an antigenic region of a protein from a first pathogen linked to a gene sequence coding for an antigenic region of a protein from a second pathogen. The pathogens particularly are parainfluenza virus (PIV) and respiratory syncytial virus (RSV). A single recombinant immunogen is capable of protecting infants and similar susceptible individuals against diseases caused by both PIV and RSV.