We estimate that there were 1.1 million symptomatic cases in the UK in 2009 955% CI = [860,000, 1,600,000]), two thirds more than the real-time estimate [ 2, 3] and 40% more than the current best HPA mid-estimate of 780,000 cases.
Across the two waves, a mid-estimate of 11.2% (7.4% to 18.9%) of the population of England were infected, rising to 29.5% (16.9% to 64.1%) in 5-14 year olds.
We present synthesis mid-point estimates of this small variation for all relevant analyses (Additional file 1: Table S2).
Mid-year estimates of English population denominators grouped by age and gender were obtained from the Office of National Statistics.
These estimates were then subtracted from the Office for National Statistics mid-year estimates of the overall population of England and Wales to derive population figures for non-South Asians.
Main outcome measures Numbers of deaths from influenza combined with mid-range estimates of numbers of cases of influenza to calculate age specific case fatality rates.
Denominator data were obtained from mid-year estimates of the population of Wales in 2004 (by Local Health Board) calculated by the Office of National Statistics for each one-year age band from the age of one to 89 years.
