Early detection of A/California/7/2004-like A(H3N2) strains in Norway during the 2004-2005 season, and emergence of a novel H3N2 genetic sub-variant toward the end.
Influenza activity in Norway during the 2004-2005 season was unusually slow in its development despite the early occurrence of an influenza A(H3N2) drift variant. Analysis of initial import and domestic cases in August-November gave early warning of a novel influenza A(H3N2) antigenic variant that had drifted further than the Southern Hemisphere A/Wellington/1/2004-like strains, and this novel variant, subsequently represented by the A/California/7/2004 vaccine strain, came to predominate in the Northern Hemisphere influenza season in most countries. After the peak of activity in mid-March, yet another H3N2 genetic variant (A/Norway/745/2005 lineage) came to predominate. While antigenically similar to A/California/2004, this new variant seems to have been able to persist in the face of increased herd immunity against the dominating variant through March-May when the major variant had vanished almost completely.
Hungnes
Olav
O
WHO National Influenza Centre, Division of Infectious Disease Control, Norwegian Institute of Public Health, P.O. Box 4404, Nydalen, N-0403 Oslo, Norway. olhu@fhi.no
D000956:Antigens, Viral / Q000276:immunology*; D014644:Genetic Variation; D006801:Humans; D053122:Influenza A Virus, H3N2 Subtype / Q000145:classification / Q000235:genetics* / Q000276:immunology / Q000302:isolation & purification; D009981:Influenza B virus / Q000145:classification / Q000276:immunology / Q000302:isolation & purification; D007251:Influenza, Human / Q000453:epidemiology / Q000821:virology*; D008969:Molecular Sequence Data; D009664:Norway / Q000453:epidemiology
D000956:Antigens, Viral