Influenza activity in Europe during eight seasons (1999–2007): an evaluation of the indicators used to measure activity and an assessment of the timing, length and course of peak activity (spread) across Europe

Table 2 Duration, spread and dominant viruses in Europe during eight influenza seasons (1999–2007)

Season	Duration	W-E (R²)	S-N (R²)	Dominant virus(es)**
1999–2000	12 weeks	0.073	0.058	A(H3N2)
2000–2001	18 weeks	0.016	0.013	A(H1N1)/B
2001–2002	15 weeks	0.331*	0.481*	A(H3N2)/B
2002–2003	15 weeks	0.428*	0.005	A(H3N2)/B
2003–2004	19 weeks	0.598*	0.001	A(H3N2)
2004–2005	18 weeks	0.680*	0.250*	A(H3N2)
2005–2006	14 weeks	0.032	0.002	A(H3N2) A(H1N1) B
2006–2007	14 weeks	0.060	0.287	A(H3N2)

Spread of influenza based on analysis of peak levels of clinical activity
W-E: West-East spread; S-N: South-North spread
R²: squared correlation coefficient (0.250; 0.331; 0.428; 0.481: moderate correlation; 0.598 and 0.680: strong correlation)
*P < 0.05
**: virus (sub)types are only listed if they represented > 20% of total detections

ISSN: 1471-2334