Antibody Persistence up to 3 Years After Primary Immunization With Inactivated Japanese Encephalitis Vaccine IXIARO in Philippine Children and Effect of a Booster Dose

Pediatr Infect Dis J. 2018 Sep;37(9):e233-e240. doi: 10.1097/INF.0000000000002124.


Background: An inactivated Vero cell culture derived Japanese encephalitis virus vaccine (IXIARO) requires a booster dose 1 year after primary schedule for long-term antibody persistence in adults. The aim of this study is to evaluate immunogenicity and safety of a booster dose in children 2 months to <18 years of age.

Methods: This is a randomized, controlled open-label study in the Philippines. Three hundred children vaccinated with IXIARO in a previous trial were randomized 1:1 to receive either no booster or a booster 12 months after initiation of the primary series. Neutralizing antibody titers were assessed before and after the booster and up to 3 years after primary series. Safety endpoints included the rate of subjects with solicited adverse events (AEs), unsolicited AEs and serious AEs within 1 month after the booster.

Results: Geometric mean titer declined by 1 year after the primary series, but titers remained above the established protective threshold in 85%-100% of children depending on age group. The booster led to a pronounced increase in geometric mean titer and 100% seroprotection rate in all age groups. The booster was well tolerated, with AE rates lower compared with the primary series. Most AEs were mild.

Conclusions: A booster dose of IXIARO administered 12 months after the primary immunization was well tolerated and highly immunogenic.

Publication types

  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Antibodies, Neutralizing / blood
  • Antibodies, Viral / blood*
  • Child
  • Child, Preschool
  • Encephalitis, Japanese / immunology
  • Encephalitis, Japanese / prevention & control*
  • Humans
  • Immunization, Secondary
  • Immunogenicity, Vaccine*
  • Infant
  • Japanese Encephalitis Vaccines / administration & dosage
  • Japanese Encephalitis Vaccines / therapeutic use*
  • Male
  • Philippines
  • Vaccines, Inactivated / administration & dosage
  • Vaccines, Inactivated / therapeutic use


  • Antibodies, Neutralizing
  • Antibodies, Viral
  • Japanese Encephalitis Vaccines
  • Vaccines, Inactivated