Comparisons with recent flu mortality

How do the number of deaths from pandemic A/H1N1 compare with influenza related mortality in recent years?1 2

The official estimate of influenza mortality is produced by the Health Protection Agency (HPA). It is derived from excess (above “expected” level) all cause death registrations in the winter. The estimates for the past five years in England and Wales are: 1965 (2004-5 winter season), 0 (2005-6), 0 (2006-7), 426 (2007-8), and 10 351 (2008-9). The highest estimate in recent years (21 497) was for the 1999-2000 flu season. This method has its limitations. It does not examine causation directly, so excess deaths may have causes other than flu. If the number of deaths is small, the estimate may be zero.

The HPA is currently reporting excess deaths weekly. At 17 December 2009, no excess deaths had been seen since February 2009. Had we relied solely on this measure, we would not have been aware of any deaths due to A/H1N1 influenza so far. Our study has value in filling this gap.

A second estimate of flu deaths is found in the annual mortality statistics produced by the Office for National Statistics. These statistics record the underlying cause of death. The number of deaths for England and Wales with an underlying cause of influenza for the four recent calendar years are: 39 (2008), 31 (2007), 17 (2006), and 44 (2005). Many more deaths are attributed to pneumonia, some of which will be secondary to influenza.

Our study includes any death with pandemic flu (or synonym) mentioned anywhere on the death certificate and any death with a laboratory positive swab for pandemic flu, irrespective of the reported cause of death. Our method has also rapidly captured information on underlying illness patterns. While absolute numbers of deaths may not be out of the ordinary, a relatively large number have occurred in children and young adults.