Comparative community burden and severity of seasonal and pandemic influenza: results of the Flu Watch cohort study

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Hayward, Andrew C. ; Fragaszy, Ellen B. ; Bermingham, Alison ; Wang, Lili ; Copas, Andrew ; Edmunds, W. John ; Ferguson, Neil ; Goonetilleke, Nilu ; Harvey, Gabrielle ; Kovar, Jana ; Lim, Megan S.C. ; McMichael, Andrew ; Millett, Elizabeth R.C. ; Nguyen-Van-Tam, J.S ; Nazareth, Irwin ; Pebody, Richard ; Tabassum, Faiza ; Watson, John M. ; Wurie, Fatima ; Johnson, Anne M. ; Zambon, Maria ; Flu Watch Group (2014)
  • Publisher: Elsevier
  • Journal: The Lancet Respiratory Medicine, volume 2, issue 6, pages 445-454 (issn: 2213-2600)
  • Related identifiers: doi: 10.1016/s2213-2600(14)70034-7

BACKGROUND: Assessment of the effect of influenza on populations, including risk of infection, illness if infected, illness severity, and consultation rates, is essential to inform future control and prevention. We aimed to compare the community burden and severity of seasonal and pandemic influenza across different age groups and study years and gain insight into the extent to which traditional surveillance underestimates this burden.<br/> METHODS: Using preseason and postseason serology, weekly illness reporting, and RT-PCR identification of influenza from nasal swabs, we tracked the course of seasonal and pandemic influenza over five successive cohorts (England 2006-11; 5448 person-seasons' follow-up). We compared burden and severity of seasonal and pandemic strains. We weighted analyses to the age and regional structure of England to give nationally representative estimates. We compared symptom profiles over the first week of illness for different strains of PCR-confirmed influenza and non-influenza viruses using ordinal logistic regression with symptom severity grade as the outcome variable.<br/> FINDINGS: Based on four-fold titre rises in strain-specific serology, on average influenza infected 18% (95% CI 16-22) of unvaccinated people each winter. Of those infected there were 69 respiratory illnesses per 100 person-influenza-seasons compared with 44 per 100 in those not infected with influenza. The age-adjusted attributable rate of illness if infected was 23 illnesses per 100 person-seasons (13-34), suggesting most influenza infections are asymptomatic. 25% (18-35) of all people with serologically confirmed infections had PCR-confirmed disease. 17% (10-26) of people with PCR-confirmed influenza had medically attended illness. These figures did not differ significantly when comparing pandemic with seasonal influenza. Of PCR-confirmed cases, people infected with the 2009 pandemic strain had markedly less severe symptoms than those infected with seasonal H3N2.<br/> INTERPRETATION: Seasonal influenza and the 2009 pandemic strain were characterised by similar high rates of mainly asymptomatic infection with most symptomatic cases self-managing without medical consultation. In the community the 2009 pandemic strain caused milder symptoms than seasonal H3N2.<br/> FUNDING: Medical Research Council and the Wellcome Trust.<br/>
  • References (45)
    45 references, page 1 of 5

    1 WHO. Influenza (seasonal): fact sheet number 211, April 2009. http:// www.who.int/mediacentre/factsheets/fs211/en/ (accessed July 1, 2013).

    2 Nguyen-Van-Tam JS, Hampson AW. The epidemiology and clinical impact of pandemic influenza. Vaccine 2003; 21: 1762-68.

    3 Luk J, Gross P, Thompson WW. Observations on mortality during the 1918 influenza pandemic. Clin Infect Dis 2001; 33: 1375-78.

    4 Oxford JS. Influenza A pandemics in the 20th century with special reference to 1918: virology, pathology and epidemiology. Rev Med Virol 2000; 10: 119-33.

    5 WHO. World now at the start of 2009 influenza pandemic: statement to the press by WHO Director-General Dr Margaret Chan (June 11, 2009). http://www.who.int/mediacentre/news/statements/2009/h1n1_ pandemic_phase6_20090611/en/index.html (accessed July 1, 2013).

    6 WHO. Swine influenza: statement by WHO Director-General, Dr Margaret Chan (April 25, 2009). http://www.who.int/mediacentre/ news/statements/2009/h1n1_20090425/en/index.html (accessed July 1, 2013).

    7 Dawood FS, Iuliano AD, Reed C, et al. Estimated global mortality associated with the first 12 months of 2009 pandemic influenza A H1N1 virus circulation: a modelling study. Lancet Infect Dis 2012; 12: 687-95.

    8 WHO. H1N1 in post-pandemic period: Director-General's opening statement at virtual press conference (Aug 10, 2010). http:// www.who.int/mediacentre/news/statements/2010/h1n1_ vpc_20100810/en/index.html (accessed July 1, 2013).

    9 WHO. Review of the 2010-2011 winter influenza season, northern hemisphere. Wkly Epidemiol Rec 2011; 86: 222-27.

    10 Mytton OT, Rutter PD, Donaldson LJ. Influenza A(H1N1)pdm09 in England, 2009 to 2011: a greater burden of severe illness in the year after the pandemic than in the pandemic year. Euro Surveill 2012; 17: 11-19.

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