A universal influenza vaccine, designed to induce broadly cross-reactive immunity against current and future influenza A virus strains, is in critical demand to reduce the need for annual vaccinations with vaccines chosen upon predicting the predominant circulating viral strains, and to ameliorate the threat of cyclically occurring pandemics that have, in the past, killed tens of millions. Here, we describe a vaccine regimen based on sequential immunization with two serologically distinct chimpanzee-derived replication-defective adenovirus (Ad) vectors expressing the matrix-2 protein ectodomain (M2e) from three divergent strains of influenza A virus fused to the influenza virus nucleoprotein (NP) for induction of antibodies to M2e and virus-specific CD8(+) T cells to NP. In preclinical mouse models, the Ad vaccines expressing M2e and NP elicit robust NP-specific CD8(+) T-cell responses and moderate antibody responses to all three M2e sequences. Most importantly, vaccinated mice are protected against morbidity and mortality following challenge with high doses of different influenza virus strains. Protection requires both antibodies to M2e and cellular immune responses to NP.