Simultaneous administration of live, attenuated influenza A vaccines representing different serotypes

Two live, attenuated cold-adapted influenza A vaccines representing current H1N1 and H3N2 serotypes were simultaneously administered intranasally to doubly seronegative children. No clinical illness resulted. Characterization of virus shedding demonstrated shedding of both original vaccine strains and of reassortant virus with the H3N1 and H1N2 phenotype. A serum immune response to both serotypes was demonstrated. The successful simultaneous administration of two influenza A vaccine strains enhances the potential usefulness of this approach to influenza prophylaxis.