Immunization with the Japanese encephalitis (JE) vaccine IXIARO® results in protective neutralizing antibody levels for one year. Since persistence of protective titer levels beyond one year was unknown, a 5 years follow-up study was conducted. Additionally, data were stratified to compare the persistence of protective neutralizing antibodies against JE in people with or without tick-borne encephalitis (TBE) vaccination. Four weeks after the primary series, the percentage of subjects with PRNT50 titer ≥1:10 in the intent-to-treat population was 99%; the rate after 5 years was 81.6%. By month 24, 36, 48 and 60, the percentages were still 90.7%, 91.7%, 90.1%, 85.9%, respectively in the population who had received TBE vaccine compared to 67.9%, 71.9%, 69.1%, 63.8% in the population who had not. No long-term safety concerns were identified. These data indicate that vaccination with IXIARO® is able to induce protective titers that persist up to 60 months after the primary immunization. Clinical trial registry number NCT00596102.
Keywords: IC51; IXIARO®; Immunogenicity; Japanese encephalitis; Safety; Seroprotection; Traveler.
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