Heterogeneity of influenza B virus strains isolated in a local area of the disease during an influenza outbreak.

Ten strains of influenza B virus isolated in a local focus during an influenza outbreak were found to include 9 virus strain variants as demonstrated by different antigenicity of their haemagglutinin, ts-marker, sensitivity to heating at 56 degrees C/30 min, and to non-specific serum inhibitors. These strains induced antibodies in rats which interacted more actively with the virus isolated in earlier periods of this outbreak than with that isolated later. It might indicate that all strains originated from the same parent strain of virus, which induced the influenza outbreak in this area.