title: Longevity of B-cell and T-cell responses after live attenuated influenza vaccination in children.
abstract: BACKGROUND
  The live attenuated influenza vaccine (LAIV) is the preferred vaccine for children, but the mechanisms behind protective immune responses are unclear, and the duration of immunity remains to be elucidated. This study reports on the longevity of B-cell and T-cell responses elicited by the LAIV.
  
  
  METHODS
  Thirty-eight children (3-17 years old) were administered seasonal LAIV. Blood samples were collected before vaccination with sequential sampling up to 1 year after vaccination. Humoral responses were evaluated by a hemagglutination inhibition assay, and memory B-cell responses were evaluated by an enzyme-linked immunosorbent spot assay (ELISpot). T-cell responses were evaluated by interferon γ (IFN-γ) ELISpot analysis, and intracellular cytokine staining of CD4(+) T cells for detection of IFN-γ, interleukin 2, and tumor necrosis factor α was performed using flow cytometry.
  
  
  RESULTS
  LAIV induced significant increases in B-cell and T-cell responses, which were sustained at least 1 year after vaccination. Strain variations were observed, in which the B strain elicited stronger responses. IFN-γ-expressing T cell counts increased significantly, and remained higher than prevaccination levels 1 year later. Expression of T-helper type 1 intracellular cytokines (interleukin 2, IFN-γ, and tumor necrosis factor α) increased after 1 dose and were boosted after the second dose. Hemagglutination inhibition titers were sustained for 1 year. Vaccine-induced memory B cell counts were significantly increased, and the response persisted for one year.
  
  
  CONCLUSIONS
  LAIV elicited B-cell and T-cell responses that persisted for at least 1 year in children. This is a novel finding that will aid future vaccine policy.
authors.affiliation: Influenza Center K. G. Jebsen Center for Influenza Vaccines.
authors.forename: Kristin G-I
authors.initials: KG
authors.lastname: Mohn
authors.affiliation: Influenza Center K. G. Jebsen Center for Influenza Vaccines.
authors.forename: Geir
authors.initials: G
authors.lastname: Bredholt
authors.affiliation: Broegelman Research Laboratory, Department of Clinical Science.
authors.forename: Karl A
authors.initials: KA
authors.lastname: Brokstad
authors.affiliation: Influenza Center K. G. Jebsen Center for Influenza Vaccines.
authors.forename: Rishi D
authors.initials: RD
authors.lastname: Pathirana
authors.affiliation: Department of Clinical Medicine, University of Bergen Department of Otolaryngology/Head and Neck Surgery.
authors.forename: Hans J
authors.initials: HJ
authors.lastname: Aarstad
authors.affiliation: Department of Clinical Medicine, University of Bergen Department of Pediatrics.
authors.forename: Camilla
authors.initials: C
authors.lastname: Tøndel
authors.affiliation: Influenza Center K. G. Jebsen Center for Influenza Vaccines Department of Research and Development, Haukeland University Hospital, Bergen, Norway.
authors.forename: Rebecca J
authors.initials: RJ
authors.lastname: Cox
mesh_terms: D000293:Adolescent; D000914:Antibodies, Viral / Q000097:blood; D001402:B-Lymphocytes / Q000276:immunology*; D002648:Child; D002675:Child, Preschool; D016207:Cytokines / Q000096:biosynthesis; D058501:Enzyme-Linked Immunospot Assay; D005260:Female; D005434:Flow Cytometry; D006385:Hemagglutination Inhibition Tests; D006801:Humans; D007252:Influenza Vaccines / Q000008:administration & dosage* / Q000276:immunology*; D008137:Longitudinal Studies; D008297:Male; D013194:Staining and Labeling; D013601:T-Lymphocytes / Q000276:immunology*; D013997:Time Factors; D014613:Vaccines, Attenuated / Q000008:administration & dosage / Q000276:immunology
chemical_list: D000914:Antibodies, Viral; D016207:Cytokines; D007252:Influenza Vaccines; D014613:Vaccines, Attenuated
keywords: IFN-γ; LAIV; T-cellular; humoral; influenza; longevity; pediatric