title: Mortality attributable to influenza in England and Wales prior to, during and after the 2009 pandemic.
abstract: Very different influenza seasons have been observed from 2008/09-2011/12 in England and Wales, with the reported burden varying overall and by age group. The objective of this study was to estimate the impact of influenza on all-cause and cause-specific mortality during this period. Age-specific generalised linear regression models fitted with an identity link were developed, modelling weekly influenza activity through multiplying clinical influenza-like illness consultation rates with proportion of samples positive for influenza A or B. To adjust for confounding factors, a similar activity indicator was calculated for Respiratory Syncytial Virus. Extreme temperature and seasonal trend were controlled for. Following a severe influenza season in 2008/09 in 65+yr olds (estimated excess of 13,058 influenza A all-cause deaths), attributed all-cause mortality was not significant during the 2009 pandemic in this age group and comparatively low levels of influenza A mortality were seen in post-pandemic seasons. The age shift of the burden of seasonal influenza from the elderly to young adults during the pandemic continued into 2010/11; a comparatively larger impact was seen with the same circulating A(H1N1)pdm09 strain, with the burden of influenza A all-cause excess mortality in 15-64 yr olds the largest reported during 2008/09-2011/12 (436 deaths in 15-44 yr olds and 1,274 in 45-64 yr olds). On average, 76% of seasonal influenza A all-age attributable deaths had a cardiovascular or respiratory cause recorded (average of 5,849 influenza A deaths per season), with nearly a quarter reported for other causes (average of 1,770 influenza A deaths per season), highlighting the importance of all-cause as well as cause-specific estimates. No significant influenza B attributable mortality was detected by season, cause or age group. This analysis forms part of the preparatory work to establish a routine mortality monitoring system ahead of introduction of the UK universal childhood seasonal influenza vaccination programme in 2013/14.
authors.affiliation: Respiratory Diseases Department, Centre for Infectious Disease Surveillance and Control, Public Health England, London, United Kingdom.
authors.forename: Helen K
authors.initials: HK
authors.lastname: Green
authors.affiliation: Statistics Department, Centre for Infectious Disease Surveillance and Control, Public Health England, London, United Kingdom.
authors.forename: Nick
authors.initials: N
authors.lastname: Andrews
authors.affiliation: Birmingham Research Unit, Royal College of General Practitioners, Birmingham, United Kingdom.
authors.forename: Douglas
authors.initials: D
authors.lastname: Fleming
authors.affiliation: Respiratory Virus Unit, Virus Reference Department, Microbiology Services, Public Health England, London, United Kingdom.
authors.forename: Maria
authors.initials: M
authors.lastname: Zambon
authors.affiliation: Respiratory Diseases Department, Centre for Infectious Disease Surveillance and Control, Public Health England, London, United Kingdom.
authors.forename: Richard
authors.initials: R
authors.lastname: Pebody
mesh_terms: D000293:Adolescent; D000328:Adult; D004739:England / Q000453:epidemiology; D006801:Humans; D007251:Influenza, Human / Q000453:epidemiology / Q000401:mortality*; D008875:Middle Aged; D014852:Wales / Q000453:epidemiology; D055815:Young Adult