Clinical Trial Info

Ixiaro as Booster After Mouse-brain Derived Vaccines for Japanese Encephalitis

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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.

Travelers 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.


Clinical Infectious Diseases published the results of this trial on June 13, 2012.

Results: In vaccine-naive travelers, the vaccination response rate for test strains Nakayama and SA14-14-2 was 100% and 87% after primary vaccination with JE-MB and 87% and 94% after JE-VC, respectively. Antibody levels depended on the target virus, with higher titers against homologous than heterologous PRNT(50) target strain (P < .001). In travelers primed with JE-MB, vaccination response rates were 91% and 91%, and 98% and 95% after a booster dose of JE-MB or JE-VC, respectively. Subgroup analysis revealed that a higher proportion of primed (98%/95%) than nonprimed (39%/42%) volunteers responded to a single dose of JE-VC (P < .001).

Conclusions: A single dose of JE-VC effectively boosted immunity in JE-MB-primed travelers. Current recommendations should be reevaluated.