Attenuated influenza virus variants comprising substitutions in NS1 that interfere with viral replication and phosphatidylinositol 3-kinase activation are described. NS1 variant polypeptides, polynucleotides encoding NS1 variant polypeptides, a reverse genetics system for producing attenuated influenza virus NS1 variants, immunogenic compositions comprising live attenuated influenza virus NS1 variants, methods of stimulating an immune response against influenza virus, methods of interfering with influenza virus replication, and methods of treating and preventing influenza virus infection are described.