One such new vaccine is a Japanese encephalitis chimeric virus vaccine (JE-CV; Imojev™; sanofi-pasteur), a live, attenuated product grown in Vero cells. The vaccine virus was constructed by removing pre-membrane and envelope coding sequences from yellow fever vaccine virus (strain 17D) and replacing them with the corresponding sequences from the attenuated JE viral strain SA14-14-2 [7] and [8]. To better inform decision-making on JE immunization, we used 5 year follow-up data on neutralizing antibody titres from JQ1 nmr a

cohort of adults who received a single dose JE-CV. These data provide in the case of Japanese encephalitis a convenient way to assess the duration of protection conferred by vaccination since the relationship between antibody levels and protection is well established: a 1:10 antibody titre is accepted by regulatory authorities [2] and [9] as a surrogate marker of protection for the licensure of new JE vaccines. A recent publication also confirmed the relevance of this threshold [10]. We used here these antibody persistence data to construct statistical models for predicting the evolution of antibody titres up to 25

years after vaccination as well as the corresponding proportion of seroprotected individuals and the median duration of protection with a single dose of JE-CV vaccine. Data for our analysis are from a randomized controlled trial, described elsewhere [11], to assess safety and immunogenicity of CT99021 clinical trial Ketanserin 1 or 2 doses of JE-CV in healthy adult volunteers recruited at a single study centre in Australia. The vaccine used in this study was produced at pilot scale as a liquid formulation

[12]. 202 individuals were screened and randomized in a 1:1 ratio to receive either JE-CV on day 0 or on day 28. At month 6, a sample of 98 participants from each group available and willing to participate received a second inoculation of JE-CV, while 103 did not. Those who received either a single dose or two doses were subsequently invited to participate in a long term follow-up study to 60 months post initial vaccination with annual immunogenicity assessments commencing at 12 months. Immunogenicity data were therefore available at days 0, 14, 28 and 56, month 6 and years 1–5. Immunogenicity assessments were based on neutralizing antibodies to JE-CV virus by plaque reduction neutralization test with a 50% endpoint (PRNT50) and are expressed as the reciprocal dilution factor (1/dil). For our analysis, we only used data from the 99 subjects who received a single-dose of JE-CV and for whom data were available at 28 days or later; 46 were still available for immunogenicity assessments by year 5. Fig. 1 shows the observed antibody titres between day 0 and year 5 in subjects receiving a single dose of JE-CV and the proportion of subjects who are seroprotected, having antibody titres ≥10.