title: Long-term Immunogenicity of a Single Dose of Japanese Encephalitis Chimeric Virus Vaccine in Toddlers and Booster Response 5 Years After Primary Immunization.
abstract: Japanese encephalitis (JE) is an important mosquito-borne viral disease that is endemic in Asia, Western Pacific countries and Northern Australia. Although there is no antiviral treatment, vaccination is effective in preventing this disease.
  
  
  
  We followed a cohort of 596 children for 5 years after primary vaccination at 12-18 months of age with JE chimeric virus vaccine (JE-CV; IMOJEV) in a multicenter, phase III trial in Thailand and the Philippines to assess antibody persistence and safety. At the end of the 5 years, a subgroup of 85 participants, at 1 site in Thailand, was followed after administration of a JE-CV booster vaccination. JE antibody titers were measured annually after primary vaccination and 28 days after booster vaccination using a 50% plaque reduction neutralization test. Seroprotection was defined as a JE-CV neutralizing antibody titer ≥10 (1/dil). Kaplan-Meier survival analysis was used to estimate the proportion of participants maintaining protective JE-CV neutralizing antibody titers.
  
  
  
  At 1, 2, 3, 4 and 5 years after vaccination with JE-CV, 88.5%, 82.9%, 78.2%, 74.0% and 68.6% of the participants followed remained seroprotected. Geometric mean titers in the subgroup assessed after receipt of a booster dose increased from 61.2 (95% confidence interval: 43.8-85.7) pre-booster to 4951 (95% confidence interval: 3928-6241) 28 days post-booster, with all participants seroprotected. There were no safety concerns identified.
  
  
  
  Protective immune responses persisted for at least 5 years after a JE-CV primary immunization in the majority of participants. JE-CV booster induced a robust immune response even after a 5-year interval.
authors.affiliation: From the *Department of Pediatrics, Srinagarind Hospital, Khon Kaen, Thailand; †Department of Pediatrics, Phramongkutklao Hospital, Bangkok, Thailand; ‡Department of Pediatrics, King Chulalongkorn Memorial Hospital, Bangkok, Thailand; §Research Institute for Tropical Medicine, Muntinlupa City, Philippines; ¶Clinical Sciences Department, Sanofi Pasteur, Marcy l'Etoile, France; and ‖Clinical Sciences and Medical Affairs Asia Department, Sanofi Pasteur, Singapore.
authors.forename: Pope
authors.initials: P
authors.lastname: Kosalaraksa
authors.forename: Veerachai
authors.initials: V
authors.lastname: Watanaveeradej
authors.forename: Chitsanu
authors.initials: C
authors.lastname: Pancharoen
authors.forename: Maria Rosario
authors.initials: MR
authors.lastname: Capeding
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Feroldi
authors.forename: Alain
authors.initials: A
authors.lastname: Bouckenooghe
mesh_terms: D000914:Antibodies, Viral / Q000097:blood* / Q000276:immunology*; D002648:Child; D002675:Child, Preschool; D004664:Encephalitis Virus, Japanese / Q000276:immunology*; D004672:Encephalitis, Japanese / Q000276:immunology / Q000517:prevention & control*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007117:Immunization, Secondary; D007223:Infant; D022321:Japanese Encephalitis Vaccines / Q000009:adverse effects / Q000276:immunology*; D008297:Male
chemical_list: D000914:Antibodies, Viral; D022321:Japanese Encephalitis Vaccines