Persistence of the immune response after vaccination with the Japanese encephalitis vaccine, IXIARO® in healthy adults: A five year follow-up study

Immunization with the Japanese encephalitis (JE) vaccine IXIARO (R) 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 (R) is able to induce protective titers that persist up to 60 months after the primary immunization. (C) 2019 The Author(s). Published by Elsevier Ltd.