title: Cross-reactive antibody responses to the 2009 pandemic H1N1 influenza virus.
abstract: BACKGROUND
  A new pandemic influenza A (H1N1) virus has emerged, causing illness globally, primarily in younger age groups. To assess the level of preexisting immunity in humans and to evaluate seasonal vaccine strategies, we measured the antibody response to the pandemic virus resulting from previous influenza infection or vaccination in different age groups.
  
  
  METHODS
  Using a microneutralization assay, we measured cross-reactive antibodies to pandemic H1N1 virus (2009 H1N1) in stored serum samples from persons who either donated blood or were vaccinated with recent seasonal or 1976 swine influenza vaccines.
  
  
  RESULTS
  A total of 4 of 107 persons (4%) who were born after 1980 had preexisting cross-reactive antibody titers of 40 or more against 2009 H1N1, whereas 39 of 115 persons (34%) born before 1950 had titers of 80 or more. Vaccination with seasonal trivalent inactivated influenza vaccines resulted in an increase in the level of cross-reactive antibody to 2009 H1N1 by a factor of four or more in none of 55 children between the ages of 6 months and 9 years, in 12 to 22% of 231 adults between the ages of 18 and 64 years, and in 5% or less of 113 adults 60 years of age or older. Seasonal vaccines that were formulated with adjuvant did not further enhance cross-reactive antibody responses. Vaccination with the A/New Jersey/1976 swine influenza vaccine substantially boosted cross-reactive antibodies to 2009 H1N1 in adults.
  
  
  CONCLUSIONS
  Vaccination with recent seasonal nonadjuvanted or adjuvanted influenza vaccines induced little or no cross-reactive antibody response to 2009 H1N1 in any age group. Persons under the age of 30 years had little evidence of cross-reactive antibodies to the pandemic virus. However, a proportion of older adults had preexisting cross-reactive antibodies.
authors.affiliation: Influenza Division, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA.
authors.forename: Kathy
authors.initials: K
authors.lastname: Hancock
authors.forename: Vic
authors.initials: V
authors.lastname: Veguilla
authors.forename: Xiuhua
authors.initials: X
authors.lastname: Lu
authors.forename: Weimin
authors.initials: W
authors.lastname: Zhong
authors.forename: Eboneé N
authors.initials: EN
authors.lastname: Butler
authors.forename: Hong
authors.initials: H
authors.lastname: Sun
authors.forename: Feng
authors.initials: F
authors.lastname: Liu
authors.forename: Libo
authors.initials: L
authors.lastname: Dong
authors.forename: Joshua R
authors.initials: JR
authors.lastname: DeVos
authors.forename: Paul M
authors.initials: PM
authors.lastname: Gargiullo
authors.forename: T Lynnette
authors.initials: TL
authors.lastname: Brammer
authors.forename: Nancy J
authors.initials: NJ
authors.lastname: Cox
authors.forename: Terrence M
authors.initials: TM
authors.lastname: Tumpey
authors.forename: Jacqueline M
authors.initials: JM
authors.lastname: Katz
mesh_terms: D000328:Adult; D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D000914:Antibodies, Viral / Q000097:blood*; D003429:Cross Reactions; D005260:Female; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology*; D007252:Influenza Vaccines / Q000276:immunology*; D007251:Influenza, Human / Q000276:immunology*; D008297:Male; D008875:Middle Aged; D009500:Neutralization Tests; D055815:Young Adult
chemical_list: D000914:Antibodies, Viral; D007252:Influenza Vaccines