Modified influenza virus NS gene segments and nucleic acid sequences encoding such modified influenza virus NS gene segments are described. In certain embodiments, a modified influenza virus NS gene segment comprises an influenza virus NS 1 open reading frame (ORF) lacking a stop codon, a heterologous nucleotide sequence, a 2A autoproteolytic cleavage site or another cleavage site, an NEP ORF, wherein the gene segment has one or more mutations in either the splice acceptor site, splice donor site, or both the splice acceptor and splice donor sites that prevents splicing of mRNA. Also recombinant influenza viruses comprising a modified influenza virus NS gene segment and the use of such viruses are described. The recombinant influenza viruses may be used in the prevention and/or treatment of influenza virus disease or as a delivery vector.
