title: Evaluation of adjuvanted pandemic H1N1(2009) influenza vaccine after one and two doses in young children.
abstract: BACKGROUND
  When Canada chose an adjuvanted influenza A H1N1(2009) vaccine for pandemic control, dosing requirements and safety in children were unknown. This study compared responses after 1 and 2 doses in young children.
  
  
  METHODS
  Five Canadian centers evaluated ASO3-adjuvanted H1N1(2009) vaccine (Arepanrix, GSK Laval, Quebec) in children aged 6 to 35 months, given 2 doses (0.25 mL, 1.9 μg hemagglutinin) 21 days apart. Blood was collected at baseline and 21 to 28 days after each dose to measure hemagglutination inhibition antibody titers. Adverse events were documented daily for 7 days after each dose.
  
  
  RESULTS
  Centers enrolled 167 children (mean age, 19 months). At baseline, 29 children (17.4%) had hemagglutination inhibition titers ≥ 10. After dose 1, titers ≥ 40 were present in 79.7% of initially naive subjects and 100% of initially primed subjects, whose respective geometric mean titers were 68 and 1020 (P < 0.001). After dose 2, 100% of subjects had titers ≥ 40, with geometric mean titers increasing to 723 in naive subjects and to 1854 in primed subjects (P < 0.001). Injection site reactions occurred in 56% of subjects after dose 1 and 43% after dose 2 (P < 0.01), with severe reactions noted in ≤ 3%. Fever >39.0°C was infrequent after either dose (5.4%, 6.6%, P = 0.20). Mild or moderate general symptoms were common but short-lived and less frequent after dose 2.
  
  
  CONCLUSIONS
  One dose of adjuvanted vaccine met criteria for licensing seasonal influenza vaccines. A second dose increased titers substantially, potentially affording greater or more durable protection. Adverse effects were common but tolerable. The use of adjuvanted seasonal influenza vaccines in young children merits consideration.
authors.affiliation: Vaccine Evaluation Center, BC Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada. dscheifele@cfri.ca
authors.forename: David W
authors.initials: DW
authors.lastname: Scheifele
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Ward
authors.forename: Marc
authors.initials: M
authors.lastname: Dionne
authors.forename: Otto
authors.initials: O
authors.lastname: Vanderkooi
authors.forename: Joanne M
authors.initials: JM
authors.lastname: Langley
authors.forename: Simon
authors.initials: S
authors.lastname: Dobson
authors.forename: Yan
authors.initials: Y
authors.lastname: Li
authors.forename: Barbara
authors.initials: B
authors.lastname: Law
authors.forename: Scott A
authors.initials: SA
authors.lastname: Halperin
mesh_terms: D000276:Adjuvants, Immunologic / Q000008:administration & dosage* / Q000009:adverse effects; D000914:Antibodies, Viral / Q000097:blood; D001769:Blood / Q000276:immunology; D002170:Canada; D002675:Child, Preschool; D005260:Female; D006385:Hemagglutination Inhibition Tests; D006801:Humans; D007117:Immunization, Secondary / Q000379:methods; D007223:Infant; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology*; D007252:Influenza Vaccines / Q000008:administration & dosage* / Q000009:adverse effects / Q000276:immunology*; D007251:Influenza, Human / Q000517:prevention & control*; D008297:Male; D014611:Vaccination / Q000379:methods
chemical_list: D000276:Adjuvants, Immunologic; D000914:Antibodies, Viral; D007252:Influenza Vaccines