title: Persistence of antibodies six years after booster vaccination with inactivated vaccine against Japanese encephalitis.
abstract: BACKGROUND
  Japanese Encephalitis (JE) virus occurs in wide regions of Asia with over 3 billion people living in areas at risk for JE. An estimated 68,000 clinical cases of JE occur every year, and vaccination is the most effective prophylactic measure. One internationally licensed vaccine containing the inactivated JE virus strain SA14-14-2 is Ixiaro (Valneva, Austria). According to recommendations, basic immunization consists of vaccinations on day 0, day 28, and a booster dose 12-24 months later. Protection in terms of neutralizing antibody titers has been assessed up to 12 months after the third dose of the vaccine. The current investigation was designed to evaluate antibody decline over time and to predict long-term duration of seroprotection after a booster dose.
  
  
  METHODS
  In a preceding trial, volunteers received basic immunization (day 0, day 28) and one booster dose against JE 15 months later. A follow up blood draw 6 years following their booster dose was carried out in 67 subjects. For antibody testing, a 50% plaque reduction neutralization test (PRNT50-test) was used. PRNT50 values of 10 and above are surrogate levels of protection according to WHO standards.
  
  
  RESULTS
  Seventy-six months following the booster dose, 96% of the tested subjects had PRNT50 titers of 10 or higher. Geometric mean titer (GMT) was 148 (95% CI confidence interval: 107-207). Antibody titers were lower in volunteers 50 years of age and older. Vaccination history against other flaviviruses (yellow fever or tick borne encephalitis) did not significantly influence PRNT50 titers. A two-step log-linear decline model predicted protection against JE of approximately 14 years after the booster dose.
  
  
  CONCLUSIONS
  Six years after a booster dose against JE, long-term protection could be demonstrated. According to our results, further booster doses should be scheduled 10 years following the first booster dose.
authors.affiliation: Institute of Specific Prophylaxis and Tropical Medicine, Medical University of Vienna, Kinderspitalgasse 15, A-1090, Vienna, Austria; Federal Ministry of Health, Austria.
authors.forename: Maria
authors.initials: M
authors.lastname: Paulke-Korinek
authors.affiliation: Institute of Specific Prophylaxis and Tropical Medicine, Medical University of Vienna, Kinderspitalgasse 15, A-1090, Vienna, Austria. Electronic address: herwig.kollaritsch@meduniwien.ac.at.
authors.forename: Herwig
authors.initials: H
authors.lastname: Kollaritsch
authors.affiliation: Institute of Environmental Health, Center for Public Health, Medical University of Vienna, Kinderspitalgasse 15, A-1090, Vienna, Austria.
authors.forename: Michael
authors.initials: M
authors.lastname: Kundi
authors.affiliation: Institute of Specific Prophylaxis and Tropical Medicine, Medical University of Vienna, Kinderspitalgasse 15, A-1090, Vienna, Austria.
authors.forename: Ines
authors.initials: I
authors.lastname: Zwazl
authors.affiliation: Institute of Specific Prophylaxis and Tropical Medicine, Medical University of Vienna, Kinderspitalgasse 15, A-1090, Vienna, Austria.
authors.forename: Claudia
authors.initials: C
authors.lastname: Seidl-Friedrich
authors.affiliation: Berlin Center for Travel and Tropical Medicine, Berlin, Germany.
authors.forename: Tomas
authors.initials: T
authors.lastname: Jelinek
mesh_terms: D000328:Adult; D000368:Aged; D057134:Antibodies, Neutralizing / Q000097:blood*; D000914:Antibodies, Viral / Q000097:blood*; D001208:Asia; D004672:Encephalitis, Japanese / Q000276:immunology / 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; D013997:Time Factors; D015164:Vaccines, Inactivated / Q000008:administration & dosage / Q000276:immunology; D010948:Viral Plaque Assay; D055815:Young Adult
chemical_list: D057134:Antibodies, Neutralizing; D000914:Antibodies, Viral; D022321:Japanese Encephalitis Vaccines; D015164:Vaccines, Inactivated
keywords: Japanese encephalitis vaccine; Long-term protection; Low responder