Characterization and clinical evaluation of live influenza a vaccine prepared from a recombinant of the A/USSR/92/77 (H1N1) and the cold-adapted A/Ann Arbor/6/60 (H2N2) strains

Live influenza vaccine was prepared after genetic recombination of the A/USSR/92/77 (H₁N₁) strain with the cold-adapted A/Ann Arbor/6/60 (H₂N₂) strain. The recombinant contains the genes coding for the HA and NA proteins from the A/USSR/92/77 (H₁N₁) strain and the genes coding for the P₁, P₂, P₃, NP, M and NS proteins from the A/Ann Arbor/6/60 (H₂N₂) strain. To assess the properties of this vaccine, it was administered under double-blind conditions to 14 healthy volunteers, while another 14 healthy volunteers received placebo.The vaccine virus appeared to be sufficiently attenuated. No febrile reactions were observed. The vaccinees showed an increase in mean serum haemagglutination-inhibiting antibody level from 19 to 73 after two vaccinations. From nasal swabs and antibody responses, it was concluded that the vaccine virus showed no transmission to the placebo group under conditions of close contact. Also, the vaccine virus was found to be genetically stable.It is concluded that this live influenza virus vaccine meets the requirements for safe use in humans. However, several problems still exist which may impede a general use of live influenza vaccines.