Reconsideration of influenza A virus nomenclature: a WHO memorandum

The system of nomenclature for influenza A viruses recommended by WHO in 1971 provided a basis for the designation of these viruses into types based on their nucleoprotein antigens. Influenza A viruses were further divided into subtypes based on the antigenic character of their haemagglutinin and neuraminidase components. To review the relevance to influenza virus nomenclature of new information on the antigenic and molecular characterization of influenza A viruses a meeting was held in Atlanta, GA, USA, in November 1978 under the auspices of WHO. Although the 1971 system of nomenclature has worked well, new information on relationships between haemagglutinin and neuraminidase subtypes indicates that the number of subtypes could be reduced. However, for the present, the participants in the meeting recommend that the 1971 system should still be used, without modification, at least until a further meeting is held in 1980. In the meantime, WHO wishes to encourage studies that will further define these relationships and solicits comments relevant to the proposals outlined in this Memorandum.