The old mouse brain derived Japanese encephalitis vaccines (MBJEV) have been reported to cause serious adverse effects and are therefore replaced with the novel Ixiaro vaccine. The present study investigates whether vaccinees primed with MBJEV can be boosted with Ixiaro.

Travellers receiving Japanese encephalitis vaccines are enrolled for a follow-up of immune responses in four groups: A) primary immunization with BMJEV, B) primary and secondary immunizations with MBJEV, C) primary immunizations with Ixiaro and S) Primary immunization with MBJEV and secondary immunization with Ixiaro. Immune responses are followed with help of serum samples collected before and after vaccination.

Inclusion Criteria:

• Male and female travellers ≥ 18 years of age.

  • General good health.
  • Written informed consent.
  • Ability to attend all visits scheduled in this study.
  • Travellers who have previously got a primary vaccination series of 2 or 3 doses of JE-MB and now receive a booster vaccination , either MB-JEV or IXIARO, at the travel clinic for their journey to Asia, OR
  • Travellers with no previous vaccination against JE who are given the primary vaccination series with IXIARO at a travel clinic prior to their journey to Asia.

Exclusion Criteria:

• - < 18 years of age.
• Acute disease at the time of enrollment.
• Pregnancy or lactation.
• Known immunodeficiency or immune suppressive treatment.
• Any chronic illness that might interfere with the immune response; history of JE.
• Alcohol or drug abuse.
• Any clinically significant history of known or suspected anaphylaxis or hypersensitivity (based on the investigator's judgement).