• 1
    Gubbels S, Perner A, Valentiner-Branth P, Mølbak K. National surveillance of pandemic influenza A(H1N1) infection-related admissions to intensive care units during the 2009–2010 winter peak in Denmark: two complementary approaches. Euro Surveill 2010; 15:19743.
  • 2
    Barry JM, Viboud C, Simonsen L. Cross-protection between successive waves of the 1918–1919 influenza pandemic: epidemiological evidence from US Army Camps and from Britain. J Infect Dis 2008; 198:14271434.
  • 3
    Andreasen V, Viboud C, Simonsen L. Epidemiologic characterization of the 1918 influenza pandemic summer wave in Copenhagen: implications for pandemic control stategies. J Infect Dis 2008; 197:270278.
  • 4
    Simonsen L, Clarke MJ, Schonberger LB, Arden NH, Cox NJ, Fukuda K. Pandemic versus epidemic influenza mortality: a pattern of changing age distribution. J Infect Dis 1998; 178:5360.
  • 5
    Statens Serum Institut. EPI-NYT. Available at (Accessed 8 June 2011).
  • 6
    Paulo AC, Correia-Neves M, Dominguos T et al. Influenza infectious dose may explain the high mortality of the second and third wave of 1918–19 influenza pandemic. PLoS ONE 2010; 5:e11655.
  • 7
    Truelove SA, Chitnis AS, Heffernan RT, Karon AE, Haupt TE, Davis JP. Comparison of patients hospitalized with pandemic 2009 influenza A (H1N1) virus infection during the first two pandemic waves in Wisconsin. J Infect Dis 2011; 203:828837.
  • 8
    Viasus D, Rodriguez-Baño J, Oteo JA et al. Changes in epidemiology, clinical features and severity of influenza A (H1N1) 2009 pneumonia in the first post-pandemic influenza season. Clin Microbiol Infect 2012; 18:E55E62.
  • 9
    Ramakrishna K, Peter JV, Karthik G et al. Influenza A (H1N1) 2009 pandemic: was there a difference in the two waves in patients requiring admission to the intensive-care unit? Clin Microbiol Infect 2011; 17:13531358.
  • 10
    Miller E, Hoschler K, Hardelid P, Stanford E, Andrews N, Zambon N. Incidence of 2009 pandemic influenza A H1N1 infection in England: a cross-sectional serological study. Lancet 2010; 375:11001108.
  • 11
    Griffin MR, Monto AS, Belongia EA et al. Effectiveness of non-adjuvanted pandemic influenza A vaccines for preventing pandemic influenza acute respiratory illness visits in 4 U.S. communities. PLoS ONE 2011; 6:e23085.
  • 12
    Skowronski DM, Janjua NZ, Serres GD et al. Effectiveness of AS03 adjuvanted pandemic H1N1 vaccine: case-control evaluation based on sentinel surveillance system in Canada, autumn 2009. BMJ 2011; 342:c7297.
  • 13
    Cheng AC, Kotsimbos T, Kelly HA et al. Effectiveness of H1N1/09 monovalent and trivalent influenza vaccines against hospitalization with laboratory-confirmed H1N1/09 influenza in Australia: a test-negative case control study. Vaccine 2011; 29:73207325.
  • 14
    Hiba V, Chowers M, Levi-Vinograd I, Rubinovitch B, Leibovici L, Paul M. Benefit of early treatment with oseltamivir in hospitalized patients with documented 2009 influenza A (H1N1): retrospective cohort study. J Antimicrob Chemother 2011; 66:11501155.
  • 15
    Rello J, Rodriguez A, Ibanez P et al. Intensive care adult patients with severe respiratory failure caused by influenza A (H1N1)v in Spain. Crit Care 2009; 13:R48.
  • 16
    Petersen E, Keld DB, Ellermann-Eriksen S et al. Failure of combination oral oseltamivir and inhaled zanamivir antiviral treatment in ventilator- and ECMO-treated critically ill patients with pandemic influenza A (H1N1)v. Scand J Infect Dis 2011; 43:495503.
  • 17
    Ariano RE, Sitar DS, Zelenitsky SA et al. Enteric absorption and pharmacokinetics of oseltamivir in critically ill patients with pandemic (H1N1) influenza. CMAJ 2010; 182:357363.
  • 18
    Fraaij PL, Vries E, Beersma MF et al. Evaluation of the antiviral response to zanamivir administered intravenously for treatment of critically ill patients with pandemic influenza A(H1N1) Infection. J Infect Dis 2011; 204:777782.
  • 19
    Han K, Ma H, An X et al. Early use of glucocorticoids was a risk factor for critical disease and death from pH1N1 infection. Clin Infect Dis 2011; 53:326333.
  • 20
    Martin-Loeches I, Lisboa T, Rhodes A et al. Use of early corticosteroid therapy on ICU admission in patients affected by severe pandemic (H1N1)v influenza A infection. Intensive Care Med 2011; 37:272283.
  • 21
    The ANZIC Influenza Investigators. Critical care services and 2009 H1N1 influenza in Australia and New Zealand. N Engl J Med 2009; 361:19251934.
  • 22
    Louie JK, Acosta M, Winter K et al. Factors associated with death or hospitalization due to pandemic 2009 influenza A(H1N1) infection in California. JAMA 2009; 302:18961902.
  • 23
    Kumar A, Zarychanski R, Pinto R et al. Critically ill patients with 2009 influenza A(H1N1) infection in Canada. JAMA 2009; 302:18721879.
  • 24
    Fuhrman C, Bonmarin I, Bitar D et al. Adult intensive-care patients with 2009 pandemic influenza A(H1N1). Epidemiol Infect 2011; 139:12021209.
  • 25
    Brandsaeter BJ, Pillgram M, Berild D, Kjekshus H, Kran AB, Bergersen BM. Hospitalised patients with suspected 2009 H1N1 in a hospital in Norway, July-December 2009. BMC Infect Dis 2011; 11:75.
  • 26
    Pakalou G, Souto J, Balcells J et al. First influenza season after the 2009 pandemic influenza: characteristics of intensive care unit admissions in adults and children in Vall d′Hebron Hospital. Clin Microbiol Infect 2012; 18:374380.
  • 27
    Gianella M, Alonso M, Viedma DG et al. Prolonged viral shedding in pandemic influenza A(H1N1): clinical significance and viral load analysis in hospitalized patients. Clin Microbiol Infect 2011; 17:11601165.
  • 28
    Meschi S, Selleri M, Lalle E et al. Duration of viral shedding in hospitalized patients infected with pandemic H1N1. BMC Infect Dis 2011; 11:140.
  • 29
    To KKW, Hung IFN, Li IWS et al. Delayed clearance of viral load and marked cytokine activation in severe cases of pandemic H1N1 2009 influenza virus infection. Clin Infect Dis 2010; 50:850859.
  • 30
    Harder KM, Andersen PH, Bæhr I et al. Electronic real-time surveillance for influenza-like illness: experience from the 2009 influenza A(H1N1) pandemic in Denmark. Euro Surveill 2011; 16:pii=19767.