title: The evolution of human influenza viruses.
abstract: The evolution of influenza viruses results in (i) recurrent annual epidemics of disease that are caused by progressive antigenic drift of influenza A and B viruses due to the mutability of the RNA genome and (ii) infrequent but severe pandemics caused by the emergence of novel influenza A subtypes to which the population has little immunity. The latter characteristic is a consequence of the wide antigenic diversity and peculiar host range of influenza A viruses and the ability of their segmented RNA genomes to undergo frequent genetic reassortment (recombination) during mixed infections. Contrasting features of the evolution of recently circulating influenza AH1N1, AH3N2 and B viruses include the rapid drift of AH3N2 viruses as a single lineage, the slow replacement of successive antigenic variants of AH1N1 viruses and the co-circulation over some 25 years of antigenically and genetically distinct lineages of influenza B viruses. Constant monitoring of changes in the circulating viruses is important for maintaining the efficacy of influenza vaccines in combating disease.
authors.affiliation: National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, UK. ahay@nimr.mrc.ac.uk
authors.forename: A J
authors.initials: AJ
authors.lastname: Hay
authors.forename: V
authors.initials: V
authors.lastname: Gregory
authors.forename: A R
authors.initials: AR
authors.lastname: Douglas
authors.forename: Y P
authors.initials: YP
authors.lastname: Lin
mesh_terms: D005075:Biological Evolution; D006801:Humans; D009980:Influenza A virus / Q000502:physiology*; D009981:Influenza B virus / Q000502:physiology*; D010802:Phylogeny; D011995:Recombination, Genetic