Figure 1: Distribution of the fold increase in antibody titres after two vaccinations.

(A) Filled circles (●) and open circles (○) denote individual volunteers designated as responders or non responders, respectively in the vaccine and placebo groups. Dotted line represents the cutoff level in fold increase of antibody titre after vaccination for grouping according to immune response based on the upper limit of the 99% CI of fold increase in the placebo group. (B) The table summarises the proportion of vaccinees designated as responder and non responder for each age cohort and vaccine dose [half- (0.5 ml) or full-dose (1.0 ml)].