Attenuated viruses and methods of designing them are disclosed. In one embodiment, there is disclosed an attenuated form of a virulent virus comprising an RNA encoding a viral protein or a nucleic acid sequence transcribable to said RNA, wherein the folding energy or structure of the RNA is changed at positions of evolutionarily conserved RNA structures with respect to that of said RNA encoding said viral protein in the virulent virus so as to bring about attenuation of the virus.

The disclosure relates to defective interfering viruses and defective interfering virus RNAs that are effective as antiviral agents. The disclosure also relates to methods for identifying defective interfering virus RNAs that can be used as effective antiviral agents.

Reported herein are presumptively de-attenuating mutations that are useful, either individually or in combinations that may include other known mutations, in producing recombinant strains of human respiratory syncytial virus (RSV) exhibiting attenuation phenotypes. Also described herein is a novel RSV construct, Min_L-NPM2-1(N88K)L, which exhibits an attenuated phenotype, is stable and is as immunogenic as wild type RSV. The recombinant RSV strains described here are suitable for use as live-attenuated RSV vaccines. Exemplary vaccine candidates are described. Also provided are polynucleotide sequences capable of encoding the described viruses, as well as methods for producing and using the viruses.

Reported herein are presumptively de-attenuating mutations that are useful, either individually or in combinations that may include other known mutations, in producing recombinant strains of human respiratory syncytial virus (RSV) exhibiting attenuation phenotypes. Also described herein is a novel RSV construct, Min_L-NPM2-1(N88K)L, which exhibits an attenuated phenotype, is stable and is as immunogenic as wild type RSV. The recombinant RSV strains described here are suitable for use as live-attenuated RSV vaccines. Exemplary vaccine candidates are described. Also provided are polynucleotide sequences capable of encoding the described viruses, as well as methods for producing and using the viruses.

The invention relates to a live-attenuated yellow fever virus strain adapted to grow on Vero cells from a parent yellow fever virus 17D substrain that is not adapted to grow on Vero cells, wherein said live-attenuated yellow fever virus strain is less neurovirulent than said parent yellow fever virus 17D substrain.

The invention relates to a live-attenuated yellow fever virus strain adapted to grow on Vero cells from a parent yellow fever virus 17D substrain that is not adapted to grow on Vero cells, wherein said live-attenuated yellow fever virus strain is less neurovirulent than said parent yellow fever virus 17D substrain.

An expression enhancer comprising a CPMV 5′UTR nucleotide sequence consisting of X nucleotides (CMPVX), where X=160, 155, 150, or 114 of SEQ ID NO:1, or consisting of a nucleotide sequence comprising from about 80% to 100% sequence similarity with CMPVX, where X=160, 155, 150, or 114 of SEQ ID NO:1 SEQ ID NO:1 is provided. The expression enhancer may further comprise a stuffer sequence fused to the 3′ end of the 5′UTR nucleotide sequence (CMPVX+, where X=160, 155, 150, or 114 of SEQ ID NO:1). The stuffer sequence may comprise one or more plant kozak sequences. Plants comprising the expression enhancer and methods using the expression enhancer are also described.

The invention is related to a dengue virus or chimeric dengue virus that contains a mutation in the 3′ untranslated region (3′-UTR) comprising a Δ30 mutation that removes the TL-2 homologous structure in each of the dengue virus serotypes 1, 2, 3, and 4, and nucleotides additional to the Δ30 mutation deleted from the 3′-UTR that removes sequence in the 5′ direction as far as the 5′ boundary of the TL-3 homologous structure in each of the dengue serotypes 1, 2, 3, and 4, or a replacement of the 3′-UTR of a dengue virus of a first serotype with the 3′-UTR of a dengue virus of a second serotype, optionally containing the Δ30 mutation and nucleotides additional to the Δ30 mutation deleted from the 3′-UTR; and immunogenic compositions, methods of inducing an immune response, and methods of producing a dengue virus or chimeric dengue virus.

Reported herein are presumptively de-attenuating mutations that are useful, either individually or in combinations that may include other known mutations, in producing recombinant strains of human respiratory syncytial virus (RSV) exhibiting attenuation phenotypes. Also described herein is a novel RSV construct, Min_L-NPM2-1(N88K)L, which exhibits an attenuated phenotype, is stable and is as immunogenic as wild type RSV. The recombinant RSV strains described here are suitable for use as live-attenuated RSV vaccines. Exemplary vaccine candidates are described. Also provided are polynucleotide sequences capable of encoding the described viruses, as well as methods for producing and using the viruses.

Reported herein are presumptively de-attenuating mutations that are useful, either individually or in combinations that may include other known mutations, in producing recombinant strains of human respiratory syncytial virus (RSV) exhibiting attenuation phenotypes. Also described herein is a novel RSV construct, Min_L-NPM2-1(N88K)L, which exhibits an attenuated phenotype, is stable and is as immunogenic as wild type RSV. The recombinant RSV strains described here are suitable for use as live-attenuated RSV vaccines. Exemplary vaccine candidates are described. Also provided are polynucleotide sequences capable of encoding the described viruses, as well as methods for producing and using the viruses.