title: Immune response to 2009 pandemic H1N1 influenza virus A monovalent vaccine in children with cancer.
abstract: OBJECTIVE
  This study investigated the immune response to 2009 pandemic H1N1 influenza monovalent vaccine in children with cancer receiving chemotherapy.
  
  
  METHODS
  We enrolled 25 pediatric patients. Ten patients younger than 10 years old received two vaccinations and the remaining 15 patients older than 10 years old received one. We checked hemagglutination-inhibition (HAI) antibody titers in sera of patients before and 3-4 weeks after vaccination. Seroprotective titer was defined as HAI antibody titer ≥ 40 and seroresponse as ≥ 4-fold increase in HAI antibody titers after vaccination.
  
  
  RESULTS
  The pre- and post-vaccination seroprotective rates were 52% and 72% (P = 0.24). Sixteen (64%) patients were possibly exposed to 2009 pandemic H1N1 influenza previously, and there was significant association between possible exposure and pre-vaccination seroprotective rate (P = 0.03). Post-vaccination seroresponse rate was 32%, and seroresponse was greater in patients without pre-vaccination seroprotective titer than those with pre-vaccination seroprotective titer (50% vs. 15%, P = 0.07). Children with lymphocyte counts above 1,500/µl during vaccination period had better seroresponse than those with lymphocyte counts below 1,500/µl (P = 0.008). Post-vaccination geometric mean titer (GMT) significantly increased in patients younger than 10 years receiving two vaccinations (pre- and post-vaccination GMT were 21.4 and 60.6, respectively; P = 0.025).
  
  
  CONCLUSIONS
  Monovalent vaccine for the 2009 pandemic H1N1 influenza A was found to be partially immunogenic in children with cancer, as evidenced by 32% of seroresponse rate. Immune response can be improved with vaccinations administered to patients whose absolute lymphocyte counts returned to a level of 1,500/µl or higher.
authors.affiliation: Department of Pediatrics, National Taiwan University Hospital, College of Medicine, National Taiwan University, Taipei, Taiwan.
authors.forename: Ting-Yu
authors.initials: TY
authors.lastname: Yen
authors.forename: Shiann-Tarng
authors.initials: ST
authors.lastname: Jou
authors.forename: Yung-Li
authors.initials: YL
authors.lastname: Yang
authors.forename: Hsiu-Hao
authors.initials: HH
authors.lastname: Chang
authors.forename: Meng-Yao
authors.initials: MY
authors.lastname: Lu
authors.forename: Dong-Tsamn
authors.initials: DT
authors.lastname: Lin
authors.forename: Kai-Hsin
authors.initials: KH
authors.lastname: Lin
authors.forename: Li-Min
authors.initials: LM
authors.lastname: Huang
authors.forename: Luan-Yin
authors.initials: LY
authors.lastname: Chang
mesh_terms: D000293:Adolescent; D000914:Antibodies, Viral / Q000097:blood; D002648:Child; D002675:Child, Preschool; D005260:Female; D006385:Hemagglutination Inhibition Tests; D006801:Humans; D007223:Infant; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology*; D007252:Influenza Vaccines / Q000276:immunology*; D007251:Influenza, Human / Q000453:epidemiology / Q000276:immunology / Q000517:prevention & control*; D008297:Male; D009369:Neoplasms / Q000276:immunology*; D058873:Pandemics
chemical_list: D000914:Antibodies, Viral; D007252:Influenza Vaccines