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Letters Seasonal vaccine and H1N1

Selection bias explains seasonal vaccine’s protection

BMJ 2009; 339 doi: (Published 24 November 2009) Cite this as: BMJ 2009;339:b4972

This article has a correction. Please see:

  1. Naveed Z Janjua, epidemiologist1,
  2. Danuta M Skowronski, epidemiologist1,
  3. Travis S Hottes, epidemiologist1,
  4. Gaston De Serres, medical epidemiologist2,
  5. Natasha S Crowcroft, director3,
  6. Laura C Rosella, epidemiologist3
  1. 1Influenza and Emerging Respiratory Pathogens, BC Centre for Disease Control, Vancouver, British Columbia, Canada
  2. 2Institut national de santé publique du Québec
  3. 3Surveillance and Epidemiology, Ontario Agency for Health Protection and Promotion Toronto, Ontario, Canada
  1. danuta.skowronski{at}

    Vaccine efficacy is estimated to be around 80% for trivalent inactivated flu vaccine during seasons when the components closely match circulating strains.1 The surface HA/NA proteins included in the 2008-9 vaccine are antigenically very distant from those of the 2009 pandemic A/H1N1 (pH1N1) virus. Few adults given the 2008-9 vaccine developed neutralising antibody against pH1N1,2 but Garcia-Garcia and colleagues report 73% (95% confidence interval 34% to 89%) cross-protection against pH1N1 with it.3 This finding probably stems from a selection bias associated with their second paradoxical …

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