title: [Evaluation of the effectiveness nine years after primary immunization with local produced plasma-derived hepatitis B vaccine].
abstract: OBJECTIVE
  To observe the effectiveness of hepatitis B vaccine nine years after primary immunization.
  
  
  METHODS
  A randomized, controlled and double-blinded trial was designed with 126 children primarily immunized with local produced plasma-derived hepatitis B vaccine nine years ago and 135 placebo-control children aged five to nine years. All the children were followed-up, their blood samples collected and their disease occurrence examined. Their hepatitis B surface antigen (HBsAg), antibody against hepatitis B core antigen (anti-HBc) and antibody against hepatitis B surface antigen (anti-HBs) were tested. Causes of lowering in their antibodies were analyzed with multivariate methods.
  
  
  RESULTS
  During the nine-year follow-up, 4% to 19% of the study subjects dropped out. In the ninth year after immunization (T108), anti-HBs positive rate in the vaccinees and their geometric mean titer (GMT) (65.3% and 5.47, respectively) were still significantly higher than those in the placebo-controls (28.3% and 1.46, respectively), but significantly lower than those in the 6th year after immunization (T72). Multivariate analysis for the causes of lowering in the antibody during the 4th, 6th and 9th year after immunization showed that antibody titer in the vaccines first year after immunization (T12) was a crucial factor for the persistence of the antibody, and natural booster might also played a certain role in it. In the T108, one clinical case of hepatitis B occurred in the placebo control group, but no cases in the vaccinees found, with a protection rate of 81.4% from HBV infection and 84.6% from HBsAg positive-coversion, similar to those in the T72.
  
  
  CONCLUSIONS
  The effectiveness of HB vaccine still existed nine years after primary immunization, and no booster dose was needed so far.
mesh_terms: D002648:Child; D004311:Double-Blind Method; D005260:Female; D005500:Follow-Up Studies; D006509:Hepatitis B / Q000517:prevention & control*; D006510:Hepatitis B Antibodies / Q000097:blood; D006512:Hepatitis B Core Antigens / Q000276:immunology; D006514:Hepatitis B Surface Antigens / Q000276:immunology; D017325:Hepatitis B Vaccines; D006801:Humans; D008297:Male; D014611:Vaccination