title: Long term immunity following a booster dose of the inactivated Japanese Encephalitis vaccine IXIARO®, IC51.
abstract: BACKGROUND
  IXIARO (IC51), a recently approved inactivated Japanese Encephalitis vaccine, is immunogenic and safe in a 0/28 days primary immunization schedule. Neutralizing antibody titers decline with time and booster doses are likely needed to enhance persistence of immunity.
  
  
  OBJECTIVE
  To assess the effect of a booster dose on neutralizing JE antibody titers for up to 12 months after boostering.
  
  
  METHODS
  In this phase III trial, 198 subjects, who had received primary immunization in a preceding randomized trial, were boosted with IXIARO 15 months after the primary immunization. Neutralizing antibody titers were assessed by plaque-reduction neutralisation test, PRNT.
  
  
  RESULTS
  Prior to the booster dose, 69.2% (137/198) of subjects had PRNT50 titers ≥ 1:10. One month after the booster, the rate of subjects with PRNT50 ≥ 1:10 (recognized as a protective titer) was 100%. This rate remained high at 98.5% at 6 and 12 months; GMTs were 22.5 before the booster and 900, 487 and 361 at 1, 6 and 12 months after the booster, respectively.
  
  
  CONCLUSIONS
  A booster dose of IXIARO at 15 months after primary immunization was highly immunogenic with GMTs >5-fold higher than those seen immediately after primary immunization, and remained at high levels for at least 12 months after the booster.
authors.affiliation: Intercell AG, Campus Vienna Biocenter 3, 1030 Vienna, Austria.
authors.forename: Susanne
authors.initials: S
authors.lastname: Eder
authors.forename: Katrin
authors.initials: K
authors.lastname: Dubischar-Kastner
authors.forename: Christa
authors.initials: C
authors.lastname: Firbas
authors.forename: Tomas
authors.initials: T
authors.lastname: Jelinek
authors.forename: Bernd
authors.initials: B
authors.lastname: Jilma
authors.forename: Astrid
authors.initials: A
authors.lastname: Kaltenboeck
authors.forename: Michael
authors.initials: M
authors.lastname: Knappik
authors.forename: Herwig
authors.initials: H
authors.lastname: Kollaritsch
authors.forename: Michael
authors.initials: M
authors.lastname: Kundi
authors.forename: Maria
authors.initials: M
authors.lastname: Paulke-Korinek
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Schuller
authors.forename: Christoph S
authors.initials: CS
authors.lastname: Klade
mesh_terms: D000328:Adult; D000368:Aged; D057134:Antibodies, Neutralizing / Q000097:blood; D000914:Antibodies, Viral / Q000097:blood; D004672:Encephalitis, Japanese / Q000517:prevention & control*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007117:Immunization, Secondary / Q000379:methods*; D022321:Japanese Encephalitis Vaccines / Q000008:administration & dosage / Q000276:immunology*; D008297:Male; D008875:Middle Aged; D009500:Neutralization Tests; D010948:Viral Plaque Assay
chemical_list: D057134:Antibodies, Neutralizing; D000914:Antibodies, Viral; D022321:Japanese Encephalitis Vaccines