title: Antibody responses after inactivated influenza vaccine in young children.
abstract: BACKGROUND
  The frequency and duration of antibody responses after trivalent inactivated influenza vaccine (TIV) in young children are not well defined and assume greater importance with the expanded recommendations for vaccine use in children aged 6 months-5 years.
  
  
  METHODS
  Forty-three children aged 6-23 months were vaccinated with TIV in the fall of 2002. At enrollment the majority of children were seronegative to one or more of the vaccine antigens and had no previously documented influenza. Postvaccination sera were collected in the subsequent fall and winter seasons. Acute antibody responses to TIV were determined using standardized hemagglutination inhibition (HAI) and neutralization assays. In calculating the duration of responses, sequential sera were analyzed to the last available sera, to the point at which antibody became undetectable, or to intercurrent influenza infection.
  
  
  RESULTS
  Forty-three subjects contributed 121 sera that were analyzed for HAI responses to TIV. Four-fold HAI rises after 2 doses of TIV in naive individuals were seen in 13 (72%) to H3N2, 22 (92%) to H1N1, and 15 (60%) to influenza B. Fewer 4-fold rises were seen in those with preexisting antibody. The results of microneutralization assays to H3N2 correlated well with HAI results. The time for antibody to decay to one-half of the postvaccination titer (t1/2) was approximately 126 days for H1N1 and 258 days for H3N2.
  
  
  CONCLUSIONS
  Although not all children responded with 4-fold rises in antibody or achieved the putative protective titer of > or =1:32, the half-life of antibody suggested that children immunized in the fall should have immune responses sustained throughout the ensuing influenza season.
authors.affiliation: Department of Pediatrics, Vanderbilt School of Medicine, Nashville, TN, USA. peter.wright@vanderbilt.edu
authors.forename: Peter F
authors.initials: PF
authors.lastname: Wright
authors.forename: Edith
authors.initials: E
authors.lastname: Sannella
authors.forename: Jian R
authors.initials: JR
authors.lastname: Shi
authors.forename: Yuwei
authors.initials: Y
authors.lastname: Zhu
authors.forename: Mine R
authors.initials: MR
authors.lastname: Ikizler
authors.forename: Kathryn M
authors.initials: KM
authors.lastname: Edwards
mesh_terms: D000914:Antibodies, Viral / Q000096:biosynthesis / Q000097:blood*; D000956:Antigens, Viral / Q000276:immunology*; D002675:Child, Preschool; D005260:Female; D006385:Hemagglutination Inhibition Tests; D006801:Humans; D007223:Infant; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology; D053122:Influenza A Virus, H3N2 Subtype / Q000276:immunology; D007252:Influenza Vaccines / Q000008:administration & dosage / Q000276:immunology*; D029521:Alphainfluenzavirus / Q000276:immunology*; D029524:Betainfluenzavirus / Q000276:immunology*; D008297:Male; D009500:Neutralization Tests; D015164:Vaccines, Inactivated / Q000008:administration & dosage / Q000276:immunology
chemical_list: D000914:Antibodies, Viral; D000956:Antigens, Viral; D007252:Influenza Vaccines; D015164:Vaccines, Inactivated