The identified technologies describe self-replicating infectious recombinant paramyxoviruses with one or more attenuating mutations, such as a separate variant polynucleotide encoding a P protein and a separate monocistronic polynucleotide encoding a V protein, or at least one temperature sensitive mutation and one non-temperature sensitive mutation. Compositions and methods for recovering, making and using the infectious, recombinant paramyxoviruses as described are also included (e.g. recombinant human parainfluenza virus type 2 (HPIV2)). In addition, these inventions provide novel tools and methods for introducing defined, predetermined structural and phenotypic changes into an infectious HPIV2 candidate for use in immunogenic compositions, including live attenuated virus vaccines. Furthermore, these inventions describe the recombinant HPIV2 P+V can be used to introduce attenuating mutations to develop live attenuated virus vaccines. The paramyxoviruses of the invention are also useful as vectors for expressing heterologous antigens (e.g. RSV, HMPV, measles or mumps viruses) in an immunogenic composition. As members of the paramyxoviruses, HPIVs are important pathogens causing severe lower respiratory tract infections in infants and young children. Despite considerable efforts, there are currently no parainfluenza virus vaccines available.

Advantages of the subject technologies to generate live attenuated viruses or vectored vaccine candidates via multiple mutations are the design of safe and stable viral vaccine candidates. Since two common vaccine development approaches (viral subunit vaccines and inactivated whole virus preparations) elicited either short-lived, inadequate immunity or unfavorable immune responses, the identified technologies provide a promising means to develop vaccines against HPIVs and other human pathogens. In addition, live attenuated viruses are the most promising candidate vaccines because they induce both local and systemic immunity and are efficacious even in the presence of passively transferred serum antibodies, the very situation found in the target population of infants with maternally derived antibodies.