title: Cross-reactive and vaccine-induced antibody to an emerging swine-origin variant of influenza A virus subtype H3N2 (H3N2v).
abstract: BACKGROUND
  Cases of infection due to a novel swine-origin variant of influenza A virus subtype H3N2 (H3N2v) have recently been identified in the United States, primarily among children. We estimate levels of cross-reactive antibody to H3N2v by age and assess whether seasonal trivalent inactivated influenza vaccine (TIV), with or without adjuvant, may increase seroprotection.
  
  
  METHODS
  Antibody to H3N2v was assessed by hemagglutination inhibition (HI) assay and, for a subset, also by microneutralization assay. Seroprevalence and seroprotection were defined as an HI titer of ≥40, and levels were compared with those for ancestral and contemporary human strains. The analysis included 1116 sera collected during fall 2010, corresponding to approximately 100 sera per decade of life. Vaccine-induced antibody levels were also assessed in sera from 136 children aged <10 years and 65 adults aged 20-59 years before and after receipt of 2010-2011 split TIV and in sera from 182 elderly individuals aged ≥65 years before and after receipt of 2011-2012 split TIV (for 31 individuals), MF59-adjuvanted TIV (for 72), or unadjuvanted subunit TIV (for 79).
  
  
  RESULTS
  The overall prevalence of HI titers of ≥40 against A(H3N2)v was 25%. No children aged <5 years and <20% of individuals aged ≤14 years or ≥40 years had an HI titer of ≥40. Conversely, among individuals aged 15-39 years, half of teens and adults showed H3N2v seroprotection. Following TIV receipt, <15% of individuals in any vaccine group developed a 4-fold increase in antibody level.
  
  
  CONCLUSIONS
  A substantial proportion of adolescents and young adults have cross-reactive antibody against emerging H3N2v, whereas children and older adults show broad susceptibility. Recent formulations of TIV do not substantially increase seroprotection. A specific vaccine would be needed if H3N2v establishes epidemic spread.
  
  
  BACKGROUND
  NCT01140009 and NCT01368796.
authors.affiliation: British Columbia Centre for Disease Control, Canada. danuta.skowronski@bccdc.ca
authors.forename: Danuta M
authors.initials: DM
authors.lastname: Skowronski
authors.forename: Naveed Z
authors.initials: NZ
authors.lastname: Janjua
authors.forename: Gaston
authors.initials: G
authors.lastname: De Serres
authors.forename: Dale
authors.initials: D
authors.lastname: Purych
authors.forename: Vladimir
authors.initials: V
authors.lastname: Gilca
authors.forename: David W
authors.initials: DW
authors.lastname: Scheifele
authors.forename: Marc
authors.initials: M
authors.lastname: Dionne
authors.forename: Suzana
authors.initials: S
authors.lastname: Sabaiduc
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Gardy
authors.forename: Guiyun
authors.initials: G
authors.lastname: Li
authors.forename: Nathalie
authors.initials: N
authors.lastname: Bastien
authors.forename: Martin
authors.initials: M
authors.lastname: Petric
authors.forename: Guy
authors.initials: G
authors.lastname: Boivin
authors.forename: Yan
authors.initials: Y
authors.lastname: Li
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D000914:Antibodies, Viral / Q000097:blood*; D002648:Child; D002675:Child, Preschool; D003429:Cross Reactions; D005260:Female; D006385:Hemagglutination Inhibition Tests; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D053122:Influenza A Virus, H3N2 Subtype / Q000276:immunology*; D007252:Influenza Vaccines / Q000008:administration & dosage / Q000276:immunology*; D007251:Influenza, Human / Q000453:epidemiology* / Q000276:immunology* / Q000517:prevention & control; D008297:Male; D008875:Middle Aged; D009500:Neutralization Tests; D016036:Seroepidemiologic Studies; D013552:Swine; D014481:United States / Q000453:epidemiology; D055815:Young Adult
chemical_list: D000914:Antibodies, Viral; D007252:Influenza Vaccines