Influenza activity remained low in the United Kingdom (UK) throughout the 2004/05 season. Clinical activity increased slowly and peaked late in the season (January to March) in comparison with the early peak in clinical activity observed in 2003/04. In England, Scotland, and Wales rates for influenza and influenza-like illness remained close to or below baseline levels and Northern Ireland, where thresholds are not used, recorded a peak in clinical activity below that of last season. Virological activity remained at low levels in England and Wales, with influenza A/Wellington/01/2004 (H3N2)-like viruses identified as the dominant circulating strain. Detections of influenza B occurred late in the season representing 15% of detections characterised by the Health Protection Agency Virus Reference Division this season and detections of respiratory syncytial virus (RSV) were at similar levels to 2003/04.

Internationally the most significant events in the season were the continuing spread of poultry outbreaks of avian influenza A (H5N1) in Asian countries, associated with sporadic cases/small clusters of human infections.

flu_2005.pdf