title: Immunogenicity of a monovalent 2009 influenza A (H1N1) vaccine among pregnant women: lowered antibody response by prior seasonal vaccination.
abstract: BACKGROUND
  Pregnant women are a high-risk group for influenza-associated complications and hospitalizations.
  
  
  METHODS
  To examine the immunogenicity of a monovalent 2009 influenza A (H1N1) vaccine among pregnant women, a prospective cohort study was performed at 2 medical institutes of obstetrics in Japan. One hundred fifty subjects received 2 subcutaneous doses of vaccine 3 weeks apart. The hemagglutination inhibition antibody titer was measured in serum samples collected at 3 time points: before vaccination, 3 weeks after the first dose, and 4 weeks after the second dose.
  
  
  RESULTS
  The first dose of vaccine induced a ≥ 10-fold rise in the average level of antibody. The seroresponse rate (≥4-fold rise) was 91%, and the seroprotection rate (postvaccination titer ≥ 1:40) was 89%. The second dose of vaccine conferred little additional induction of antibodies. Similar immune responses were observed irrespective of body mass index before pregnancy, trimester, or age at vaccination. However, lesser immune response was shown in subjects who had received the 2009-2010 seasonal influenza vaccine before the H1N1 vaccination.
  
  
  CONCLUSIONS
  A single dose of vaccine induced an adequately protective level of immunity in pregnant women. The potential interference with seasonal vaccination requires a more thorough investigation to prepare for future influenza pandemics.
authors: Department of Public Health, Osaka City University Graduate School of Medicine, Osaka City Juso Hospital, Japan. satop@med.osaka-cu.ac.jp
authors: Satoko
authors: S
authors: Ohfuji
authors: Wakaba
authors: W
authors: Fukushima
authors: Masaaki
authors: M
authors: Deguchi
authors: Kazume
authors: K
authors: Kawabata
authors: Hideki
authors: H
authors: Yoshida
authors: Hideaki
authors: H
authors: Hatayama
authors: Akiko
authors: A
authors: Maeda
authors: Yoshio
authors: Y
authors: Hirota
mesh_terms: D000293:Adolescent; D000328:Adult; D000914:Antibodies, Viral / Q000097:blood*; D015331:Cohort Studies; D005260:Female; D006385:Hemagglutination Inhibition Tests; D006801:Humans; D007115:Immunization Schedule; D007117:Immunization, Secondary / Q000379:methods; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology*; D007252:Influenza Vaccines / Q000008:administration & dosage* / Q000276:immunology*; D007279:Injections, Subcutaneous; D007564:Japan; D011247:Pregnancy; D011446:Prospective Studies; D014611:Vaccination / Q000379:methods*; D055815:Young Adult
chemical_list: D000914:Antibodies, Viral; D007252:Influenza Vaccines