title: Recent changes among human influenza viruses.
abstract: Recurrent epidemics of influenza are due to the frequent emergence of antigenic variants. With co-circulation of two influenza A subtypes and two antigenically distinct lineages of B viruses, genetic reassortment also has an important role in antigenic drift, as illustrated by recent changes in both A and B viruses. The H1N2 subtype viruses, which emerged during 2001, possessed a H1 HA similar to those of contemporary A/New Caledonia/20/99 (H1N1)-like viruses and seven genes closely related to those of recent H3N2 viruses, and did not represent a significant increase in the antigenic diversity of circulating viruses. The re-emergence of B/Victoria/2/87-lineage viruses, previously prevalent during the 1980s, in 2000 has been followed by the predominant circulation of reassortant B viruses possessing a B/Victoria-lineage HA and a B/Yamagata-lineage NA similar in sequence to those of recent B/Sichuan/379/99-like viruses. These events emphasize not only the lack of divergence in the complementary functional characteristics of the HA and NA of divergent influenza B lineages, but also the apparent convergence in compatibility between the H1 and N2 components of the two influenza A subtypes.
authors.affiliation: Virology Division, National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, UK.
authors.forename: Y P
authors.initials: YP
authors.lastname: Lin
authors.forename: V
authors.initials: V
authors.lastname: Gregory
authors.forename: M
authors.initials: M
authors.lastname: Bennett
authors.forename: A
authors.initials: A
authors.lastname: Hay
mesh_terms: D000940:Antigenic Variation; D019143:Evolution, Molecular; D006801:Humans; D009980:Influenza A virus / Q000145:classification / Q000235:genetics*; D009981:Influenza B virus / Q000145:classification / Q000235:genetics*; D007251:Influenza, Human / Q000453:epidemiology* / Q000821:virology; D016865:Reassortant Viruses