title: Long term effectiveness of adjuvanted influenza A(H1N1)pdm09 vaccine in children.
abstract: BACKGROUND
  Immunological studies have indicated that the effectiveness of AS03 adjuvanted monovalent influenza A(H1N1)pdm09 vaccine (Pandemrix) may be of longer duration than what is seen for non-adjuvanted seasonal influenza vaccines. Sixty-nine percent of children 6 months-18 years of age in Stockholm County received at least one dose of Pandemrix during the 2009 pandemic. We studied the effectiveness of the vaccine during the influenza seasons 2010-2011 and 2012-2013 in children hospitalized with virologically confirmed influenza. The season 2011-2012 was not included, since influenza A(H3N2) was the predominant circulating strain.
  
  
  METHODS
  In a retrospective case-control study using a modified test-negative design we compared the percentage vaccinated with Pandemrix among children diagnosed with influenza A(H1N1)pdm09 (cases), with that of those diagnosed with influenza A(H3N2) or influenza B (controls) during the two seasons. We excluded children born after July 1, 2009, since only children who were 6 months of age or older received the pandemic vaccine in October-December 2009.
  
  
  RESULTS
  During the 2010-2011 season, 3/16 (19%) of children diagnosed with influenza A(H1N1)pdm09, vs. 32/41 (78%) of those with influenza A(H3N2) or influenza B had been vaccinated with Pandemrix in 2009. The odds ratio, after adjustment for sex, age and underlying diseases, for becoming a case when vaccinated with Pandemrix was 0.083 (95%CI 0.014, 0.36), corresponding to a VE of 91.7%. During the season 2012-2013, there was no difference between the two groups; 59% of children diagnosed with influenza A(H3N2)/B and 60% of those with influenza A(H1N1)pdm09 had been vaccinated with Pandemrix in 2009.
  
  
  CONCLUSIONS
  The AS03 adjuvanted monovalent influenza A(H1N1) pdm09 vaccine (Pandemrix) was effective in preventing hospital admission for influenza A(H1N1)pdm09 in children during at least two seasons.
authors: Karolinska Institutet, Department of Medicine, Unit of Infectious Diseases, Karolinska Solna, Stockholm, Sweden; Department of Communicable Disease Control and Prevention, Stockholm County Council, Box 175 33, SE-118 91 Stockholm, Sweden. Electronic address: ake.ortqvist@sll.se.
authors: Åke
authors: Å
authors: Örtqvist
authors: Astrid Lindgren Children's Hospital, Karolinska University Hospital, Solna, SE-171 76 Stockholm, Sweden.
authors: Rutger
authors: R
authors: Bennet
authors: Astrid Lindgren Children's Hospital, Karolinska University Hospital, Solna, SE-171 76 Stockholm, Sweden.
authors: Johan
authors: J
authors: Hamrin
authors: Sachs' Children and Youth Hospital, Stockholm South General Hospital, Sjukhusbacken 10, SE-118 83 Stockholm, Sweden.
authors: Malin Ryd
authors: MR
authors: Rinder
authors: Astrid Lindgren Children's Hospital, Karolinska University Hospital, Huddinge, SE-141 86 Stockholm, Sweden.
authors: Hans
authors: H
authors: Lindblad
authors: Department of Communicable Disease Control and Prevention, Stockholm County Council, Box 175 33, SE-118 91 Stockholm, Sweden.
authors: Joanna Nederby
authors: JN
authors: Öhd
authors: Astrid Lindgren Children's Hospital, Karolinska University Hospital, Solna, SE-171 76 Stockholm, Sweden.
authors: Margareta
authors: M
authors: Eriksson
mesh_terms: D000276:Adjuvants, Immunologic; D000293:Adolescent; D000914:Antibodies, Viral / Q000097:blood; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data; D006801:Humans; D007223:Infant; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology*; D053122:Influenza A Virus, H3N2 Subtype / Q000276:immunology; D007252:Influenza Vaccines / Q000008:administration & dosage / Q000276:immunology*; D007251:Influenza, Human / Q000175:diagnosis / Q000453:epidemiology / Q000517:prevention & control*; D008297:Male; D016017:Odds Ratio; D058873:Pandemics; D012189:Retrospective Studies; D012621:Seasons; D013548:Sweden / Q000453:epidemiology; D013997:Time Factors; D014611:Vaccination / Q000706:statistics & numerical data
chemical_list: D000276:Adjuvants, Immunologic; D000914:Antibodies, Viral; D007252:Influenza Vaccines; C556153:pandemrix
keywords: Children; Effectiveness; Long term; Pandemic; Vaccination