• Four major immunological types of virus (A, B, C, and D) are now known to cause influenza; each comprises a completely distinct group. Within type A are variants with marked antigenic differences, and groups of these strains comprise sets or families. In May, 1957, representative strains from a new set, now termed Far East (FE) or Asian influenza A were isolated from epidemics of influenza in Singapore. Only slight antigenic similarity is evident between the FE viruses and other type A influenza strains. Serologic diagnosis may be made with either hemagglutination-inhibition or complement-fixation tests with the new antigens.
Jensen KE. NEW SET OF TYPE A INFLUENZA VIRUSES. JAMA. 1957;164(18):2025-2029. doi:10.1001/jama.1957.02980180027007