Variation of influenza A (H3N2) viruses isolated in the G.D.R. during 1969-1980 epidemics

A collection of 39 influenza A virus strains of the subtype H3N2 isolated in G.D.R. and of six reference strains were analysed with regard to the antigenic structure of their surface proteins haemagglutinin (HA) and neuraminidase (NA) as well as regarding their polypeptide variations. For the field strains during the drift period from spring 1969 to spring 1980 seven main variations resulted from eight polyclonal sera with the haemagglutination inhibition test, and five main variations from six polyclonal sera with the neuraminidase inhibition test. Using the polyacrylamide gel electrophoresis polypeptide variations in HA, nonstructural proteins NS1, NS2 and nucleoprotein (NP) were detected. It could be shown that, even during one epidemic, strains circulated with different polypeptide composition. With the help of peptide mapping further variations of NP and NS1 were registered. The mechanisms leading to the emergence of new epidemic strains are discussed.