This is a prospective, double-blinded, multicenter, randomized, pivotal Phase 3 study comprising approximately 750 subjects aged 12 years to <18 years randomized in a 2:1 ratio to the live-attenuated CHIKV vaccine candidate (VLA1553) or placebo. The final dose of lyophilized VLA1553 or placebo will be administered as a single intramuscular immunization. Subjects in this study will be stratified by baseline serostatus. The primary objective of the study is to evaluate the immunogenicity and safety of the adult dose of VLA1553 28 days following the single immunization. Immunogenicity evaluations in the immunogenicity subset will include the proportion of subjects with seroprotective neutralizing CHIKV antibody titers above a surrogate threshold indicative of protection. The surrogate of protection reasonably likely to predict clinical benefit has been established in non-human primate passive transfer studies using human sera from the Phase 1 study. Safety data collection and immunogenicity will continue to be assessed until Month 12.
This is a prospective, randomized, double-blinded, multicenter, pivotal study evaluating the final dose of VLA1553 (1 x10E4 TCID50 per dose) in comparison to a placebo control. The final dose of VLA1553 or control will be administered as single immunization on Day 1. Overall, approximately 750 male and female subjects aged 12 years to <18 years will be enrolled into the study.