Comparison of the immune response to variant influenza type B hemagglutinins expressed in vaccinia virus

To compare the immune response induced by influenza hemagglutinin (HA) variants differing by a single amino acid, the genes for each HA variant were cloned and expressed in vaccinia virus. These variant HA genes have been previously described as being present exclusively in either egg-derived or MDCK cell-derived subpopulations of influenza B/England/222/82 virus. By using this approach we were able to vaccinate animals with homogeneous preparations of these viral antigens and thus circumvent the problem of heterogeneity within RNA virus stocks. Immunization and challenge experiments in mice indicated that even though vaccination with the recombinant vaccinia viruses induced different levels of cross-reactive neutralizing antibodies, mice vaccinated with either recombinant vaccinia virus were protected from infection with either subpopulation of influenza virus. Results with this model system support the view that influenza vaccines prepared with egg-derived virus should be protective against microvariants of virus that grow preferentially in MDCK and possibly other mammalian cells.