The first year following vaccination, the predicted seroprotection rate is high but decreases quite rapidly (−2.3% between day 28 and year 1). The seroprotection rate declines at a slower rate during the second year than during the first (−0.4%) but then accelerates from this point onwards. This can be seen by a steeper curve after year 5. In particular, at year 5 the predicted seroprotection is 94.7% (95% CI: 90.9–97.9) which is comparable
to the observed value of 93.3% (95% CI: 82.1–98.6). At 10 years the predicted seroprotection level still remains high at 85.5% (95% CI: 72.7–94.9). We calculated the percentiles for duration selleck products of protection in our study population, or equivalently, the percentage of individuals having at least the given duration of protection http://www.selleckchem.com/products/bmn-673.html by maintaining antibody titres above the accepted threshold. The maximum, median and minimum duration
of protection were calculated to be respectively 38.1 years, 21.3 years and less than 28 days. Excluding the 2 subjects who were not seroprotected at 28 days (vaccine non responders), all subjects had at least 3.4 years of protection and 90% of subjects had at least 11.2 years of protection. Table 3 gives the percentiles for duration of protection in our study population excluding the 2 non-responders. The change point for antibody decay refers to the time when the initial period of rapid decline in titre ends and the second period of slow decline begins. The average individual change point, as estimated by the 2-period piecewise-linear
PD184352 (CI-1040) model, was 0.267 years (5th to 95th percentile range: 0.11–0.61). This means that antibody titres after a single dose of JE-CV would continue to decline rapidly from their peak value observed around day 28 until 3.2 months after vaccination on average (5th to 95th percentile range: 1.4–7.3). After this initial period of rapid antibody decline, titres continue to decline but at a much slower rate (about 50 times slower). Our analyses of the persistence of antibodies predict that the seroprotection rate after a single dose of JE-CV in adults remains high for at least 10 years. This conclusion is based on a median antibody titre at 10 years of 38, which exceeds the seroprotective threshold of 10 accepted by regulatory authorities as a surrogate marker of protection [9]. Overall, we predicted that 85.5% of subjects will maintain antibody titres above the threshold value 10 years after vaccination. The median duration of seroprotection exceeded 20 years, and 90% of responding subjects had at least 11.2 years of protection. We also inferred from our analyses that there is an early, short period of rapid antibody decline ending during the 4th month after vaccination (3.2 months on average), after which a second period of much slower antibody decay ensues for many years.