Influenza M2 protein mutant viruses as live influenza attenuated vaccines

An immunogenic composition comprising an isolated, live, in vivo attenuated recombinant influenza virus comprising a PA viral gene segment, a PB1 viral gene segment, a PB2 viral gene segment, a HA viral gene segment, a NA viral gene segment, a NP viral gene segment, a M viral gene segment having coding sequences for M1 and M2, and a NS viral gene segment having coding sequences for NS1 and NS2, wherein the M gene segment comprises a mutant M2 protein gene for a M2 protein which has a deletion consisting of 2 to 21 residues of the C-terminus of the cytoplasmic tail which M2 protein is encoded by the mutant M2 protein gene, wherein the deletion attenuates the replication of the recombinant virus in vivo relative to the corresponding influenza virus without the deletion, wherein the amount of the virus in the composition is about 0.1 micrograms to 200 micrograms of influenza virus hemagglutinin (HA) per influenza virus isolate or about 103 to 107 PFU per influenza virus isolate.