title: Measuring antibody responses to a live attenuated influenza vaccine in children.
abstract: BACKGROUND
  Hemagglutination inhibition (HAI) assay is the standard method for evaluating inactivated influenza vaccines, but no standard assay has been established for evaluating live attenuated influenza vaccines (LAIV). LAIV containing A/Beijing/262/95(H1N1) induced low serum HAI antibody responses to the antigenic variant, A/New Caledonia/20/99(H1N1) in a serologic study but provided protection against the A/New Caledonia-like viruses in a community study. Neutralization and HAI assays were compared by measuring H1N1 cross-reactive antibody responses to the LAIV in children.
  
  
  METHODS
  Sera were collected from 50 children 1-8 years of age before vaccination and 4-6 weeks after each dose of the LAIV. Antibody titers to the 3 vaccine viruses were measured by the HAI assay, whereas antibody titers against the H1N1 vaccine virus (A/Beijing/262/95) and 2 H1N1 antigenic variants (A/Shenzhen/227/95 and A/New Caledonia/20/99) were measured by the HAI and neutralization assays.
  
  
  RESULTS
  Initially seronegative participants were more likely to develop HAI seroconversion responses to the 3 vaccine viruses than the baseline seropositive participants (77% versus 14% for H1N1, 100% versus 20% for H3N2, 100% versus 19% for B, P < 0.01, Fisher's exact test). For the H1N1 cross-reactive antibody responses, seroconversion rates measured by the neutralization assay were significantly higher than those measured by the HAI assay (95% versus 78%, P = 0.0485 for A/Beijing/262/95; 75% versus 24%, P < 0.0001 for A/Shenzhen/227/95; 51% versus 5%, P < 0.0001 for A/New Caledonia/20/99).
  
  
  CONCLUSIONS
  The neutralization assay was more sensitive than the HAI assay for measuring H1N1 antibody responses after vaccination of children with the LAIV and may provide a better correlate of clinical protection provided by the LAIV.
authors.affiliation: MedImmune Vaccines, Mountain View, CA, USA.
authors.forename: Min-Shi
authors.initials: MS
authors.lastname: Lee
authors.forename: Kutubuddin
authors.initials: K
authors.lastname: Mahmood
authors.forename: Lopa
authors.initials: L
authors.lastname: Adhikary
authors.forename: Marilyn J
authors.initials: MJ
authors.lastname: August
authors.forename: Julie
authors.initials: J
authors.lastname: Cordova
authors.forename: Iksung
authors.initials: I
authors.lastname: Cho
authors.forename: George
authors.initials: G
authors.lastname: Kemble
authors.forename: Keith
authors.initials: K
authors.lastname: Reisinger
authors.forename: Robert E
authors.initials: RE
authors.lastname: Walker
authors.forename: Paul M
authors.initials: PM
authors.lastname: Mendelman
mesh_terms: D000914:Antibodies, Viral / Q000032:analysis*; D000917:Antibody Formation / Q000276:immunology; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D016001:Confidence Intervals; D005260:Female; D005500:Follow-Up Studies; D006385:Hemagglutination Inhibition Tests; D006801:Humans; D007115:Immunization Schedule; D007252:Influenza Vaccines / Q000008:administration & dosage / Q000276:immunology*; D007251:Influenza, Human / Q000276:immunology* / Q000517:prevention & control; D008297:Male; D011336:Probability; D014611:Vaccination; D014613:Vaccines, Attenuated / Q000008:administration & dosage / Q000276:immunology
chemical_list: D000914:Antibodies, Viral; D007252:Influenza Vaccines; D014613:Vaccines, Attenuated