Vivaldi is developing its deltaFLU live attenuated influenza vaccine to provide broad cross-protection and superior efficacy in the prophylaxis of seasonal and pandemic influenza. deltaFLU is composed of influenza vaccine strains modified by deletion of the gene for nonstructural protein 1, an interferon antagonist. Following intranasal administration, deltaFLU induces interferon, achieving a self-adjuvant effect that stimulates cellular and humoral immune responses. In a heterologous challenge trial in the ferret model, deltaFLU shows superior protection against widely drifted influenza H1N1, H3N2, and B strains versus a leading licensed quadrivalent vaccine. In clinical trials, deltaFLU shows potent immunogenicity and induces broadly cross-reactive antibodies, including mucosal antibodies that cross-neutralize heterologous influenza subtypes, and serum antibodies that cross-neutralize drift variants. Phase 1 and 2 clinical studies also show that deltaFLU is safe, replication-deficient, and not shed by the recipient. deltaFLU is produced in a high-efficiency, high-yield Vero cell production process, providing significant advantages in speed, scale-up, and cost, and eliminating mutations that may reduce efficacy of egg-produced vaccines.