Protection afforded by intranasal immunization with the neuraminidase-lacking mutant of influenza A virus in a ferret model.

Protective efficacy of the intranasal immunization with the neuraminidase (NA)-deficient mutant of the influenza A virus was investigated in ferrets. Despite the highly attenuated replication in vivo, the mutant completely protected the animals against the wild type virus challenge. When challenge was done with antigenic drift variants, significant reductions in the viral titers, inflammatory cell counts, and protein concentrations were observed in the nasal washes of the immunized animals. The genetically engineered NA-deficient mutant also protected animals against the challenge and induced humoral immune response against the foreign protein that replaced the NA. We conclude that the NA as antigen is dispensable in the live attenuated influenza virus vaccine and that the NA-lacking mutant can be used as a virus vector.