Antigenic and amino acid sequence variations in the haemagglutinins of type A influenza viruses recently isolated from human subjects.

Since 1978, influenza A viruses with different antigenic properties have been isolated in many countries, even though little influenza activity has been recorded. In the present paper, the antigenic properties of viruses representative of isolates from each year since 1979 are compared, and the amino acid sequences of their haemagglutinins are described in detail. The reults give an indication of the extent and nature of variation in influenza A viruses during this period.